Search

The Valle del Cura region, located in the High Central Andes, over the Pampean flat-slab segment, exhibits several geothermal manifestations suggesting structural rather than magmatic controls. However, the structural and favorable conditions of this geothermal system have not been studied in detail yet. By integrating high-resolution airborne geophysical data with existing geological information using GIS tools, we can better characterize the structural controls of the thermal areas. The application of the upward continuation filter and tilt-angle derivative to the reduced to pole magnetic anomaly map allowed us to delineate structural lineaments that correlate well with known faults in the area. Euler deconvolution successfully identified local structures controlling the subsurface water upwelling and provided reliable depth estimations. Results indicate that the Despoblados area is characterized by NW-oriented deep structural controls reaching depths of up to 5 km. In contrast, the Bañitos-Gollete and the northern thermal areas are controlled by the intersection of N-S with E-W shallow structures at less than 3 km deep. Aeroradiometric data provided additional information for the characterization of several lithological units based on the dominance of radioelements (K, Th and U) in near-surface rocks by using individual and ternary maps. In addition, estimations of radiogenic heat production were crucial for assessing the potential energy of geothermal resources in the region. In particular, higher average values were obtained for igneous and metamorphic basement which may contribute to the geothermal gradient and temperature distribution at depth. Further studies, including new geophysical data acquisition and field verification, are still needed to fully describe the regional and local structures involved in these geothermal areas. • Geothermal manifestations in Valle del Cura suggest structural controls due to the absence of active volcanism. • Airborne geophysical data combined with geological data improved the understanding of structural controls and heat sources. • Results indicate deep NW-oriented structural controls up to 5 km depth in Despoblados. • Southern and northern thermal areas are controlled by the intersection of N-S with E-W shallow structures at less than 3 km deep. [ABSTRACT FROM AUTHOR]

The late Eocene-Early Miocene intra-arc Abanico extensional basin represents a major feature in central Chile (∼31°-42°S). Such basin system concentrated the magmatic activity along this Andean region and hosted locally more than 3.000 m of volcanic and volcaniclastic deposits (Abanico Formation) over a southward thinning crust (<35 km thick). South of 34°30′S, major changes occur in and out of the basin realm that modify the rather regular distribution of the geological features observed northwards, namely: 1. Southward termination of the exposures of the Farellones Formation, 2. Increased presence of pre-Abanico volcanic and plutonic exposures in the basin realm, 3. Southward width increase of the basin, 4. Abrupt end in the Maule region of the Cretaceous plutonic swaths exposed in the eastern Coastal Cordillera and westward bend of the swaths of Mesozoic units, 5. Increased presence of primitive volcanic rocks in the west-side of the basin, and 6. Presence, south of 36°S, of the Cura-Mallín Formation on the east-side of the basin. These changes are caused by the oblique orientation of the Abanico basin relative to the Mesozoic structural and paleogeographic trends and are enhanced by the increased southward opening of the basin. This opening would have occurred through a westward scissors-like rotation of the block of continental crust located west of the basin, which corresponds to the present-day Coastal Cordillera south of 34°30′S. The eastern border, which is represented by the El Diablo fault, remained essentially fixed. The westward rotation is supported by the north-northeast orientation of the Mesozoic plutonic and stratified swaths south of 34°30′S. Additionally, the swaths of Mesozoic rocks are obliquely interrupted by the similarly oriented western border of the basin. Previous analogue models designed to understand the opening and closure mechanisms of an extensional basin show that greater extension and subsidence in the basin occur next to the mobile border, which in the Abanico basin was located on its west side. This observation aligns with the increased southward presence of primitive volcanic rocks, like the Colbún Formation, in the region where crustal thinning would have been greater. Analogue models show that the increased southward extension allowed the development of wider depocenters. In the Maule region, an eastern depocenter near the El Diablo fault, hosted the Early to Middle Miocene deposits of the Cura-Mallín Formation. During contraction, deeply rooted reverse faults can involve basement rocks of the basin and bring them up to the surface as observed in the Abanico basin realm in the Tinguiririca and Maule regions. This study also highlights the continuity and importance of the El Diablo fault in the configuration of the basin. It is shown that, notwithstanding the existence of major changes south of 34°30′S, this fault represents a major structural element that remained unchanged along the Andean segment comprised between ∼32° and 36°30′S separating the Cenozoic deposits to the west from Mesozoic deposits to the east. This fault can be traced continuously from, at least, the Aconcagua valley (33°S) to the Maule region (36°30′S), and most probably extends further south. Apart from separating the Cenozoic Abanico basin deposits from the Mesozoic units involved in the east-vergent Andean fold-thrust belt, its trace forms an almost straight line that connects the Palomo, Tinguiririca, Planchón-Peteroa, Descabezados, San Pedro and Rezago volcanic centers and complexes, hot-springs, and hydrothermal alterations. [Display omitted] • The opening of the Abanico basin occurred by W-ward rotation of its W-border; the El Diablo fault is the fixed E-border. • The basin southward width increase caused major crustal thinning in the south region allowing ascent of primitive magmas. • El Diablo fault controlled the extensional/contractional activity on the basin E-side and the present volcanic activity. • The westward rotation of the western limiting block of the basin caused the NNE-SSW trend of the Mesozoic plutonic swaths. [ABSTRACT FROM AUTHOR]

The Laguna del Maule (LdM) volcanic field, which surrounds the 54-km2 lake of that name, covers ∼500 km2 of mountainous glaciated terrain with Quaternary lavas and tuffs that extend 40 km westward from the Argentine frontier and 30 km north-south from the Río Campanario to Laguna Fea. Complementing recent investigations of postglacial volcanism and the ongoing geophysical unrest around the lake, we here review the longer eruptive history that spanned the entire Quaternary. The distributed rear-arc LdM volcanic field is contiguous with the Tatara-San Pedro stratovolcano complex on the volcanic front of the Quaternary Andean arc. The LdM field has had only a few large edifices, but we identified at least 140 separate vents, from which >350 km3 of products have erupted since 1.5 Ma. Eruptive products of 14 (early and middle Pleistocene) stratocones and shields, and of ∼125 monogenetic cones, domes, and lava flows, were mapped on foot, studied petrographically, and chemically analyzed. More than 80 40Ar/39Ar and K-Ar ages have been determined to calibrate the Pleistocene eruptive sequence. An extensive welded ignimbrite erupted at 1.5 Ma and was followed by another at ∼950 ka, producing a 12 x 8 km-wide caldera that underlies the north part of the lake basin and the ruggedly eroded highlands north of it. Outside the caldera, the southern two-thirds of the lake basin is a drainage network cut on Tertiary andesites and dacites. A ring of ∼29 postglacial rhyolite and rhyodacite coulees and domes plus associated pyroclastic deposits that erupted from >30 separate vents (and together cover ∼100 km2) encircles the lake. The large number of postglacial silicic vents around the lake basin, several comagmatic multi-vent compositional arrays, and scarcity of mafic enclaves in the rhyolites are features that suggest growth of a latest Pleistocene to Holocene magma reservoir beneath the LdM Basin. The Barrancas center on the divide southeast of the Basin has an additional 21 lavas from 15 vents and represents a second independent postglacial rhyolitic reservoir. About 21 postglacial mafic and intermediate eruptive units accompany the rhyolites around the margins of the LdM Basin. Ongoing work by Fierstein et al. (this volume) has brought the total number of postglacial vents recognized to more than 73 and has determined ∼70 radiocarbon dates that bracket the abundant tephra deposits, thus providing a 17,000-year-long calibration of the postglacial eruptive sequence. In addition to the many postglacial silicic units, glacially eroded silicic lavas yield ages of 3.7, 2.5, 2.4, 2.0, 1.6, and 1.35 Ma, and 924, 880, 712, 695, 680, 460, 335, 240, 203, 114, 97, 83, and 25 ka, providing evidence of a prolonged history of explosive silicic eruptions from vents scattered throughout the volcanic field. Production of widely distributed rhyolites throughout the long history of the volcanic field demonstrates intensive crustal processing as well as the enduring potential for explosive eruptions. For the Quaternary LdM volcanic field, chemical analyses define an array continuous from 49% to 77.6% SiO 2 , medium-K toward its mafic end (1.5% K 2 O @ 55% SiO 2) but high-K at its silicic end (4.5% K 2 O @ 75% SiO 2). Quaternary eruptive units include 5 basalts, ∼30 mafic andesites (52–57% SiO 2), 33 andesites, 11 dacites (63–68% SiO 2), 25 rhyodacites, ∼27 rhyolites (>72% SiO 2), and 6 ignimbrites (andesitic to rhyolitic). None of the basalts is primitive, and most of the mafic rocks display petrographic and/or chemical evidence for diverse crustal contributions (Hildreth et al., 2010). • Laguna del Maule volcanic field produced >140 vents in 2 million years. • >80 radioisotopic dates calibrate the eruptive sequence, which was virtually continuous throughout the Quaternary. • Rhyolite erupted repeatedly throughout the Pleistocene and Holocene. • Several large Pliocene and Pleistocene silicic foci preceded the recently active rhyolitic system. [ABSTRACT FROM AUTHOR]

Strontium isotopic ratios (⁸⁷Sr/⁸⁶Sr) in sedimentary and igneous rocks may provide valuable interpretations that allow constraining the geologic evolution of sedimentary basins. We present a new ⁸⁷Sr/⁸⁶Sr dataset from sedimentary units in the southern Central Andes (33°–34°S)—coupled to available isotopic information of igneous rocks—to examine the paleogeographic evolution of the Andes at the western margin of South America during the Mesozoic. These new data was obtained from shales, limestones and fine-grained sandstones from Mesozoic formations in the Coastal Cordillera and the Principal Cordillera of the main Andes. The new Sr-isotopic data on the Mesozoic sedimentary rocks can be grouped by both rock type and location: a) Continental red sandstones: 0.7038–0.7124; b) Calcareous rocks of the main Andes (Principal Cordillera): 0.7070–0.7081; and c) Calcareous rocks of the Coastal Cordillera: 0.7041–0.7067. The ⁸⁷Sr/⁸⁶Sr signatures in most of the clastic units in both Cordilleras are related to an evolved or enriched magmatic source for clasts and matrix indicating different sources. On the other hand, the Sr-isotopic composition of calcareous rocks differs between the units in the Andean and the Coastal mountain belts: shales and limestones in the Principal Cordillera of the Andes display ⁸⁷Sr/⁸⁶Sr ratios corresponding to the contemporary ocean in the Late Jurassic and Early Cretaceous; whereas the carbonatic units in the Coastal Cordillera do not show a relation with any oceanic signatures. The Sr-isotopic compositions of the Andean carbonatic units in the Principal Cordillera support the interpretation of their marine depositional environment in the paleo Pacific Ocean. In contrast, carbonate rock samples from the formations in the Coastal Cordillera suggest that they formed in brackish-water depositional basins made by topographic highs partially disconnected from the ocean. In the case of clastic rocks, their Sr-isotopic compositions provide insights into the contributions derived from the magmatic arc to the clastic units. Therefore, the Sr-isotopic composition of the sedimentary rocks provides a new dataset which can improve our understanding of the geological evolution of the southern Central Andes. • A new set of 87Sr/86Sr ratios for Mesozoic sedimentary rocks in the Southern Andes. • The 87Sr/86Sr of calcareous rocks varies across the Andean and Coastal cordilleras. • 87Sr/86Sr in calcareous rocks in the Andes correspond to the contemporary ocean. • 87Sr/86Sr in calcareous rocks in the Coastal range indicate continental sources. • The contrasting 87Sr/86Sr accros the margin have paleogeographic implications. [ABSTRACT FROM AUTHOR]

Structural control is one of the most important factors in developing the karstic system since the fractures facilitate the infiltration and circulation of groundwater. This accelerates the mineral dissolution processes responsible for the formation of endo and exokarstic geomorphological features, such as sinkholes and underground cavities, among other landforms that characterize this environment. This study provides information on the structural geology of the El Peñón karstic system, considered one of the most significant and extensive karstic regions in Colombia. The karst is tectonically controlled by joints with a preferential NW-SE orientation and cleavage planes with an NE-SW trend, guiding the development of drainage systems, closed depressions, and underground cavities. The stress tensor obtained with a NW-SE direction (127°) explains the deformation in the area and its influence on the development of the karstic system. It was also established that the potential groundwater flow occurs through open fractures with a direction of 120°–130° (parallel to the stress tensor) and along the cleavage planes (40°–50°). The fracture patterns are characterized by intermediate intensity values, predominantly low fracture density, minimal lengths, and good connectivity between fracture planes. • The exokarstic system is mainly controlled by cleavage and Mode I structures. • Gentle folds defining the Los Yariguíes Anticlinorium at a regional level. • The calculated stress tensor for the zone has an Shmax of 127°. • The mechanical coherence of the structures is explained by the same stress field. • Two potential fluid transit directions are proposed: 110°–140° and 40°–50°. [ABSTRACT FROM AUTHOR]

This study encompasses a geochemical investigation of Cretaceous source rocks from the Eastern Cordillera (Colombia). This basin represents an interesting area for geochemical studies due to its abundance of organic matter-rich levels, some of which exhibit mild to extremely high thermal maturities, enabling discussion on long-term carbon sinks. This research work focuses on the study of organic-rich shaly sediments of Barremian to Campanian age from seven (7) outcrop locations in two areas of the Boyacá Department. A set of seventy (70) rock samples have been analysed using several organic geochemical techniques and have shown to cover thermal maturity ranges from the early oil window to the metagenesis stage (measured reflectance values from 0.6% to 2.1%). The OAE2 event was identified based on a 2.5‰–3‰ carbon isotopic excursion in the distal Guaguaquí Group from the section along the Guaquaquí River. Maturity was not found to correlate with depositional burial depths in the so-called distal study area, suggesting that other tectonic events may have played an important role in the genetic history of hydrocarbons particularly in this part of the Boyacá Department. During the mid-to late Cretaceous times, the two study areas consisted of a marine margin with a terrestrial input from the east, which is reflected in a higher terrestrial character of sediments in the eastern foothills (V/Ni < 0.7) compared to the others. Finally, fluorene- and diamondoid-based components were used for enhancing the characterization of the mid-to late Cretaceous organic matter in terms of source in the study sub-region (three-fluorenes and dimethyl-/trimethyl-adamantanes ratios above or below 0.25 and 0.85). • The Eastern Cordillera is one of the most prolific petroliferous regions of Colombia. • Organic geochemistry of Cretaceous strata in the foothills of the East Andes (Boyacá). • Comparing the depositional settings and maturities of study source types in Boyacá. • Using aromatic hydrocarbons and diamondoid-based proxies for source characterization. • Assessing novel molecular geochemical parameters at very high thermal maturity levels. [ABSTRACT FROM AUTHOR]

The Holocene sedimentary history of the Turbio River valley in semi-arid north-central Chile and its relationship to climate variability is presented in this study. Fluvial landforms and sedimentary deposits serve as essential records for studying the long-term dynamics of fluvial systems in response to external factors such as tectonic and climatic influences. The study area, located in the Andean Mountain range, is highly sensitive to hydrodynamic changes and sediment transport processes, making it suitable for studying fluvial dynamics and their relationship to climate fluctuations over millennia. In particular, the transitional semi-arid conditions of this region provide an opportunity to link Holocene fluvial sediments to climatic shifts. This study presents the analysis of well-preserved sedimentary deposits that outcrop along the valley walls, including grain-size distribution, stratigraphy, geochemical composition and radiocarbon dating to establish the chronological context. Facies association analysis, along with geochemical data, allowed the interpretation of depositional sub-environments and their evolution through time. We interpret the Holocene sedimentary evolution for the Turbio River valley as six time periods that reflect shifts in sediment source, energy regime, flow types, and sedimentary processes linked to fluctuations between wet and dry climatic conditions. The sedimentary sequence is interpreted as reflecting an initial high-energy period with continuous surface runoff followed by two periods of formation of extensive lakes, likely separated by periods of runoff intensification. The later part of the sequence reflects a more stable fluvial landscape that led to the excavation of the sedimentary fill. This sedimentary record provides valuable insights into past climate variations and their impact on the hydrodynamic conditions of the fluvial system in the region. Comparisons with other regional records support a broader understanding of climate change in the semi-arid Andes of Chile. • Rio Turbio sedimentary record is studied to reconstruct Holocene river dynamics. • Fluctuations in fluvial processes are related to alternating wet and dry periods. • A new model explains how the river evolved in response to Holocene climate variations. • Fluvial record provide valuable insights into past climates. [ABSTRACT FROM AUTHOR]

The Salares Norte (SN) Au–Ag belt is here defined as an Upper Miocene-Pliocene metallogenic area, extending for nearly 200 km, located NE of the northern end of the Upper Oligocene-Lower Miocene Maricunga Belt in the central Andes of northern Chile. The belt is located just east of the main reverse NS fault systems which are part of the Sierra Castillo, Potrerillos Mine and Claudio Gay Cordillera faults, limited to the north and south by the NW-striking oblique to the arc Imilac and Wheelwright-Incahuasi regional faults systems. The epithermal deposits within the SN belt are intimately associated with the occurrence of Middle Miocene volcaniclastic basins and Middle to Upper Miocene phreatomagmatic vents and their related high-sulfidation hydrothermal systems. The volcanostratigraphy of the SN epithermal belt comprises volcaniclastic sequences, subvolcanic and volcanic rocks ranging between the Lower Miocene and the Pliocene. High-angle NS reverse faults involving Paleozoic and lower Cenozoic units form the western-southwestern limit of the belt. Folded and faulted Middle Miocene volcaniclastic and volcanic sequences form the main host rock of at least 4 phreatomagmatic events that generated maar-diatreme fields and discrete maar vents, with their related subvolcanic facies, within the widespread Upper Cenozoic volcanic arc, ranging in age between ca. 15 and ca. 4 Ma. These four phreatomagmatic events are spatially and temporarily associated to 4 main high-sulfidation hydrothermal events which have altered both the phreatomagmatic rocks and the Cenozoic country rock of the explosive activity. These hydrothermal systems have formed dozens of discrete hydrothermally altered areas where argillic, advance argillic, silicification and steam-heated alteration are common. Most of the maar fields and the hydrothermal alteration systems are emplaced within a strike-slip tectonic regime with NE-trending shortening which is accommodated in the NW-striking sinistral-normal faults and NE-striking extension structures. These fault systems crosscutting interaction favor the hydrothermal fluid circulation and migration, as well as mineral precipitation on structural and/or primary lithological traps and on NE-striking tension cracks. In summary, the SN epithermal belt is an almost 200 km long and 60 km wide area, mainly NNE-oriented, where epithermal deposits have formed during the Upper Miocene and Pliocene (ca. 13-4 Ma), emplaced within Middle to Upper Miocene volcanic and volcaniclastic sequences associated to small volcanotectonic basins oriented in NS, NE-SW and NW-SE directions, in which most of the high-sulfidation systems are associated to discrete or repetitive structurally-controlled Upper Miocene-Pliocene phreatomagmatic vents and maar fields. • This paper defines a new Au–Ag epithermal belt in the Central Andes of northern Chile. • Novel results in terms of age, volcanic stratigraphyand hydrothermal alteration. • The relationships between Upper Cenozoic HS epithermal areas, local tectonics and phreatomagmatic volcanism are discussed. [ABSTRACT FROM AUTHOR]

The Cenozoic subsidence and uplift history in southern Patagonia have been influenced by tectonic shortening, sub-lithospheric forces, and climate. The Patagonian Andes mountain-building resulted mainly from shortening and glacial erosion, whereas the extra-Andean foreland was mainly influenced by flexural and subcrustal-driving forces, which drove marine transgressions and plateau-like topography. However, there are some regional features in Patagonia that cannot be fully explained considering the proposed geodynamic scenario. The Deseado Massif in south-central Patagonia is formed mainly by Jurassic rocks overlapped by Paleogene and Neogene basalts. The lack of Oligocene and Neogene strata in this area has been associated with a paleo-relief formed previous to the Oligo-Miocene marine transgressions. This study aims to explore and investigate the likely mechanisms related to the formation of this paleo-topography. This requires analyzing and revising the Cenozoic paleogeography, subsidence and uplift history of southern Patagonia, and its connection with crustal tectonics and the influence of the asthenospheric mantle. This study utilized a combination of methodologies, including analysis of decompaction and backstripping to investigate subsidence and uplift history. These results were compared with flexural loading models constructed from the most recent structural reconstructions. Our investigation shows strong temporal and spatial differences in the subsidence distribution. The comparison of subsidence models suggest that tectonic shortening and loading during the Oligocene and Early Miocene (30–20 Ma), derived from palinspastic studies, had to be much lower than proposed by structural reconstructions. During Neogene, in contrast, the tectonic loads might explain the subsidence records relatively well. From our analyses, the maximum flexural relief could explain the exposition of the Deseado Massif region with respect to the rest of the extra Andean valleys during the Oligo-Miocene marine incursion. To the north of the massif, this uplift was recorded by the tectonic subsidence curves, which show a symmetric upwarping zone that could be associated with reduction in the accommodation space during the bulge zone development. Based on these observations, we propose that the uplift of the Deseado Massif took place during the Oligo-Miocene period, driven by flexural uplifting. Subsequent Neogene subsidence and uplift histories were superimposed on this preexisting flexural topography generating the modern paleogeography. The results have implications for the tectonic history and paleogeographic reconstructions of southern Patagonia, and shed light on the interactions between tectonic and geodynamic processes during the Oligocene-Miocene and their consequences in the foreland evolution of Southern Patagonia. • Backstripping and flexural loading models are compared to shed light on subsidence and uplift history. • Tectonic shortening and loading during 30–20 Ma stage had to be much lower than previously proposed. • Subsidence is related to tectonic loading and long-wavelength subcrustal processes • The uplift of the Deseado Massif took place during the Oligo-Miocene period, driven by flexural uplifting. • Subsequent Neogene subsidence and uplift histories were superimposed on this preexisting flexural topography. [ABSTRACT FROM AUTHOR]

A high-precision earthquake catalog was generated using source-specific station terms and waveform cross-correlation techniques. This detailed catalog serves to interpret the crustal structure and deformation related to the tectonic setting in Northwestern South America. The Panamá-Chocó Block (PCB) is in contact with the Northwestern Andes causing crustal deformation and hence, fault interaction in the brittle regime leading to a high earthquake production concentrated in the Murindó Seismic Cluster (MSC) which is located in the northeastern corner of the PCB. Slip on the Uramita Fault Zone (UFZ) is a response to the accommodation of the PCB against the North Andean block (NAB), splitting the fault into two segments, marked by an abrupt change in its strike. The north segment of the UFZ, a dextral transform fault (strike = S52°E and near vertical plane), which produced the Mutatá earthquake (2016-09-14, Mw = 6.2). The central segment of the UFZ strikes N12°E and exhibits mainly reverse slip with a subvertical fault plane which produced the 1987-03-19 Mw = 5.4 and 1987-11-11 Mw = 5.3 events. The Murindó sinistral strike-slip fault (strike = N9°W), which produced the great Murindó earthquake (1992-10-18, Mw = 7.1, epicentral intensity XI) is characterized by its wide zone of brittle deformation as a response to internal deformation of the PCB under a compressional NW-SE stress. Intermediate depth earthquakes are widely observed in the area, where we find evidence of the Caribbean slab subducting southwards beneath Panamá. The subduction of the Malpelo microplate to the south, shows high productivity within the Cauca Cluster and the presence of at least three finger-shaped mantle zones of seismicity. [ABSTRACT FROM AUTHOR]

Understanding what produces and how to detect fertile magmas, capable of forming large, economic porphyry-type deposits, is not only a major scientific quest, but it is also relevant economically, as it could lead to better exploration models and higher success rates in mineral exploration. In this work, we use new and previous geochemical and geochronological data from the Mio-Pliocene metallogenic belt of Central Chile to assess the existing tools to detect fertile magmas, study their spatiotemporal variations at different scales and discuss the geological and exploration implications of our findings. Our results suggest that the geochemical ratios currently used to detect fertile magmas are effective, as there is a good correlation between fertile signatures and the presence of known porphyry Cu deposits and prospects, with few false positives, which might be explained by the exhumation and erosion of most of the metal-rich part of the hydrothermal systems. Regarding the genesis of fertile magmas, the spatiotemporal variations we document here are not satisfactorily explained by the processes commonly brought forward to produce this type of intrusions, such as crustal thickening and subduction of sediments, crustal fragments or oceanic fracture zones. These processes operate at regional- or continental-scales in entire arc segments, while magma fertility shows strong contrasts in several coeval intrusions separated only by a few kilometers or tens of kilometers, emplaced within the same arc segment, under the same tectonic regime, crustal thickness and subduction parameters. This implies that there is a strong local control on the production of fertile magmas. Our results support the notion that the most important variable affecting the generation of fertile magmas in subduction margins, is magma residence time at different crustal levels. This variable has a strong local control, as it will depend not only on the overall crustal thickness or the regional tectonic regime, but also on the local orientation of structural pathways controlling magma ascent through the crust, relative to the predominant stress tensor. If magma pathways are oriented at higher angles relative to the maximum stress, magma residence times will be longer, allowing the fractionation of abundant hornblende (giving the residual magma its characteristic fertile or "adakite-like" signature) and the accumulation of magmatic sulfides which can be remobilized by later magmatic pulses; becoming progressively more oxidized due to intra-crustal processes; and concentrating large amounts of incompatible volatiles and metals in the residual melts. This can explain the strong variability observed in magma fertility in nearby coeval intrusions, and also in cross-cutting intrusions separated by very short time periods, which might have followed different ascent pathways. Our results also suggest that the Teno-Maule segment, in the southernmost part of the Mio-Pliocene metallogenic belt, shows striking differences in magma fertility patterns compared with the rest of the belt. There, fertile magmas are scarce and, contrary to the northern part of the belt, there is no evidence of an enhanced magma fertility during the late Miocene – early Pliocene. • Fertile magmas are those capable of forming large porphyry Cu deposits. • We discuss the spatiotemporal patterns of magma fertility observed in Central Chile. • Long-term fertility patterns are different for specific arc segments. • A strong local variability on fertility patterns is observed, within arc segments. • Local variability related to differences in the structural controls on magma ascent. [ABSTRACT FROM AUTHOR]

Late Oligocene-early Miocene aridification in the retroarc foreland basin adjacent to the southern central Andes was recorded by widespread eolian conditions that coincided with accelerated subsidence driven by the main phase of Andean tectonic loading. An extensive eolian dune system, which is rare in most foreland basins, indicates specific conditions in terms of climate (aridity), atmospheric circulation, orography, sediment sources, dispersal patterns, and accommodation space. Detrital zircon U-Pb geochronological results for eolian sandstones spanning 20 foreland localities in northwestern to west-central Argentina, from 22°S to 36°S, reveal relatively localized Andean sources rather than regional cratonic provenance. Clastic detritus was largely derived from Phanerozoic igneous and sedimentary rocks of the Andean magmatic arc and retroarc fold-thrust belt during initial shortening-induced uplift of hinterland regions such as the Western Cordillera, Principal Cordillera, and Frontal Cordillera. This provenance record provides the earliest evidence for major westerly winds, transporting Andean detritus broadly eastward to the foreland basin (with common axial northward deflections) during a climate shift marked by the latest Oligocene-earliest Miocene inception of arid conditions. In addition to the climatic implications, independent stratigraphic data provide the basis for a compilation of sediment accumulation histories showing that eolian deposition was synchronous with accelerated subsidence attributable to enhanced Andean shortening. We propose that accelerated Andean uplift in the latest Oligocene-early Miocene generated rain-shadow conditions contemporaneous with increased sediment accommodation in the foreland basin, underscoring the important influence of tectonic processes on regional climate. • Latest Oligocene-early Miocene aridification in the Andean foreland basin (22-36°S) recorded by widespread eolian conditions. • Eolian sand deposition coincided with accelerated subsidence during inception of major Andean shortening and tectonic loading. • Foreland aridification and westerly winds represent the growth of an orographic rain shadow induced by Andean uplift. • Zircon U-Pb provenance data show local Andean sources and east-directed eolian transport with northward (axial) deflections. • Orographically modulated climate and tectonically driven accommodation space helped govern Andean foreland basin evolution. [ABSTRACT FROM AUTHOR]

Torrential flows represent one of the most catastrophic natural hazards in the Andes, and Colombia is not an exception. We computed and analyzed ten morphometric indexes, classified by the catchment geometry and relief characteristics, for 149 torrential catchments across Colombian Andes three branches (Western, Central, and Eastern cordilleras). We divided the study area into six tectonic-stratigraphic regions, and employed statistical tests such as the Shapiro-Wilk and ANOVA One-Way Permutation tests to assess index distributions within each region. The ANOVA One-Way Permutation test results revealed significant differences in the distributions of form factor (p -value 0.048), mean gradient (p -value 0.009), relief ratio (p -value 0.003), Melton ratio (p -value 0.006), and hypsometric integral (p -value 0.000) indices among regions. Likewise, the pairwise comparison tests identified that the following regions are different between them for Melton ratio: Central Cordillera and Plateau Antioqueño (p -value 0.032), Garzón Massif and Plateau Antioqueño (p -value 0.015), Garzón Massif and Santander Massif (p -value 0.05), and Plateau Antioqueño and Western Cordillera (p -value 0.032); for relief ratio: Central Cordillera and Plateau Antioqueño (p -value 0.0219), Estern Cordillera and Plateau Antioqueño (p -value 0.0425), Garzón Massif and Plateau Antioqueño (p -value 0.0058), Plateau Antioqueño and Western Cordillera (p -value 0.053); for hypsometric integral: Central Cordillera and Western Cordillera (p -value 0.0004), Eastern Cordillera and Western Cordillera (p -value 0.0004), Garzón Massif and Western Cordillera (p -value 0.0004), Plateau Antioqueño and Western Cordillera (p -value 0.0161), and Santander Massif and Western Cordillera (p -value 0.002). Based on the findings we computed confidence intervals for the population median of the studied morphometric parameters according to the region employing a non-parametric bootstrapping method. The statistical analysis highlights the importance of the geological and geomorphological features in the morphometric indices analysis as part of the torrential flow susceptibility assessment. Applying our findings, we tested proposed thresholds in a case study of the Santander Massif (Eastern Cordillera of Colombia), focusing on the 2020 Piedecuesta Flow. In the study case, we demonstrated the relevance of identifying the feeder catchments where the morphometric indices would be calculated from, especially in areas where significant hydrologic changes occur. Volumetric concentration variations along the Piedecuesta Flow path highlight the need to prioritize the recognition of feeder catchments as an imperative part of the susceptibility assessment. Our approach enriches the knowledge base for identifying torrential-prone basins and has important implications for natural hazard management, aiming at mitigating the impact of torrential flows in the Andes. • New quantitative data proves the North Andes are prone to torrential flows. • Some morphometric features of the catchments are characteristic of specific geomorphological regions. • Torrential flows in Colombia exhibit a broad distribution across diverse geological and geomorphological settings. • In most cases, the thresholds of morphometrical index which characterize the tropical torrential watersheds differ from those regions much less humid. [ABSTRACT FROM AUTHOR]

The Capitana mine, Tignamar District, is a unique Sn-Bi concentration in the highlands of Arica, in the Chilean Central Andes. Tin deposits associated with Triassic to Pliocene age igneous rocks are plentiful in the Tin Belt of Peru, Bolivia, and NW Argentina, but have not been reported in Chile, where contemporaneous rocks formed metallogenic belts rich in Fe, Cu, Mo, Ag and Au. We describe vein ore from Capitana mine, a small but exceptional Sn-bearing Pb-Bi-Ag-Cu-Sb-As epithermal deposit in the Tignamar (or Ticnamar) district in the high Andes of Arica, Chile, ca. 250 km west of the Bolivian Tin Belt. Fluid inclusions in vein quartz trapped a non-boiling, low salinity (<∼4 wt% NaCl equiv.), moderate T fluid (minimum T ∼ 220 °C) prior to metal precipitation. Flashing of this fluid, likely due to rapid changes in confining P, was synchronous with metal deposition; sulfosalt textures show evidence of syn-deformational growth. Although located within a district considered a porphyry copper system of Early Miocene age, it is likely that the Capitana deposit formed later, mainly as a result of regional hydrothermal activity related to compressive and transpressional tectonics as young as Pliocene. Common lead is 206Pb/204Pb 18.18; 207Pb/204Pb 15.61; and 208Pb/204Pb 38.53, significantly less radiogenic than that of Bolivian Sn deposits, and has a Paleozoic model lead age. These values point to affinities with a tectonically-emplaced inlier of crystalline basement of Proterozoic – Early Paleozoic age known as the Belen Metamorphic Complex, and with the Arequipa-Antofalla basement terrane, a probable remnant of Laurentia (North America), left behind during the dismemberment of the Rodinia Supercontinent. The complex mineralogy of Capitana vein, unlike other Chilean deposits, includes various sulphides and sulphosalts with Cu, Fe, Zn, Pb, Bi, Sn, Ag, As, Sb, Ga and In, and is exceptionally rich in U. [ABSTRACT FROM AUTHOR]

In the southernmost sector of the Central Volcanic Zone (CVZ), spanning from 23° to 28°S, there is an estimated count of 30–40 potentially active volcanoes. Due to its remote location, the primary volcanic threat in this area during explosive eruptions is the dispersal and fallout of tephra. Among various approaches, tephrochronological studies have proven to be the most effective in compiling a comprehensive record of recent explosive eruptions in this region. The intermontane valleys nestled at the eastern foothills of the Andes, situated around 200–300 km from the volcanic arc, harbor a Holocene stratigraphic record containing multiple layers of tephra. These layers are evidence of the recurrence of substantial volcanic eruptions (VEI ≥4) during recent times, particularly within the last 10,000 years. Improving the tephrochronological knowledge of the southernmost edge of the CVZ constitutes a crucial initial step in evaluating the ash-fall hazard of this region. In this context, the Tafí valley emerges as a prominent candidate for serving as a dependable tephrochronological "anchor point" for regional correlations. Its strength lies in its conspicuous record of Holocene tephras and its well-documented morpho-stratigraphic setting, which has been rigorously constrained by absolute age dating. Despite these advantages, some of the Holocene tephras found within Tafí valley remain uncharacterized in terms of both glass shard and mineral geochemistry. This limitation has consequently hindered their utility in facilitating regional correlations. Thus, we present the glass shard and mineral composition of these uncharacterized Holocene tephras previously identified within Tafí valley. Our findings have not only enhanced regional correlations beyond the Tafí valley but have also provided more precise source constraints. Ultimately, our work represents an upgrade of the Holocene tephrochronological framework of Northwestern Argentina and a stride toward a more reliable assessment of volcanic hazard and risk within the region. • Geochemical fingerprints for the Holocene tephras of the Tafí Valley were found. • The Fingerprint allows for the correlation of the tephras on a regional scale. • The novel data presented here allowed us to better assess the possible source of each tephra. • This work is a stride toward a more reliable assessment of volcanic hazards of NW Argentina. [ABSTRACT FROM AUTHOR]

Inselbergs are isolated rock bodies that develop as a result of differential weathering and erosion advances during topographic etchplain formation. The timing and rate of inselberg growth are key for constraining external controls on landscape evolution, particularly in etching terrains associated with elevated plateaus carved on granitic lithologies, and in tectonically active provinces in tropical climate zones (e.g., Antioqueño Plateau, AP). We applied new morphostratigraphic and geomorphometric analyses, along with 10Be terrestrial cosmogenic nuclide (TCN) measurements, to in situ rock samples from the Peñol de Guatapé Inselberg (PGI), in the AP of the Colombian Andes to address the chronological framework of bornhardt formation in this tropical setting. The PGI is located in a rejuvenated landscape between middle Miocene to late Mio-Pliocene erosion surfaces. Erosion rates inferred from 10Be analyses ranged between ∼0.0024 ± 0.0001 and 0.24 ± 0.0283 mm/yr. This broad range is consistent with the long-term erosion rate of ∼0.04 mm/yr and mid-term erosion rates of 0.01–0.08 mm/yr previously documented for the region using low-temperature thermochronology. Our findings indicate that the PGI emerged as an important landscape feature over a period of ∼0.5–2.0 Myr and has protruded high above the average AP surface since the Pliocene. The new TCN-derived erosion-rate estimates for the AP Inselberg enable us to better understand the role of weathering and erosional processes that controlled the evolution of landscape surfaces during Andean orogenic cycles documented in the region. • El Peñol de Guatapé Inselberg (PGI) is the largest bornhardt in the Antioqueño Plateau (AP). • The (AP) is the most extensive and best-preserved planation surface in the Northern Andes. • The PGI lies in a rejuvenated landscape of the AP between erosion surfaces of middle Miocene to late Mio-Pliocene age. • In situ 10Be concentrations suggest million-year scale erosion rates between 0.0024 and 0.24 mm/yr. • PGI formation occurred during the Pliocene as a result of erosional and tectonic forcing. [ABSTRACT FROM AUTHOR]

This study investigates the provenance of middle-late Miocene to Pliocene sediments of the Solimões Formation, in western Brazilian Amazonia, to complement the geological history and fill the gap left by similar studies on other foreland basin deposits and in the Amazonian fan. The major and trace element concentrations and Sr–Nd isotopic compositions of sixteen samples from the 1AS 33AM borehole and fifteen samples from two sections outcropping in the Acre and Yaco rivers were measured for determining their provenance. Additionally, the heavy mineral assemblages of the sixteen borehole samples were determined to complement the geochemical provenance interpretation of the borehole sediments. The Nd isotopic compositions of the Solimões Formation indicate that the Andes was the principal source of these Neogene sediments. While the middle-late Miocene borehole sediments are dominated by stable assemblage (zircon, tourmaline, and rutile) and less radiogenic Nd isotopic values, the Pliocene borehole sediments have a larger amount of more unstable mineral assemblages (epidote, pyroxene, and amphibole) and more radiogenic Nd isotopic values. These mineral and isotopic differences between the middle-late Miocene and Pliocene sediments are interpreted to reflect a change in provenance with increasing contribution of metamorphic and young Nd radiogenic source in the Pliocene most probably related to the late Miocene uplift of the Peruvian Eastern Cordillera. These changes that precede the paleoenvironmental changes highlighted by the palynological study of Leite et al. (2017) suggest that the Andean tectonics drove the middle to late Miocene paleoenvironmental changes of the Amazon basin from the Pebas mega-wetland to the more fluvial Acre phase. • Nd isotopic ratios and heavy mineral indicate an Andean source for Neogene sediments of the Solimões Formation. • Metamorphic heavy minerals and Nd isotopic ratios suggest contribution from the Peruvian Eastern Cordillera for Pliocene sediments. • Middle to late Miocene paleoenvironmental changes in the Acre basin driven by uplift of Eastern Cordillera and Andean Building. [ABSTRACT FROM AUTHOR]

Cotopaxi is a stratovolcano in the Northern Volcanic Zone of the Andes, and has a history of bimodal volcanism, alternating between rhyolite and andesite. With Cotopaxi reawakening in 2015 after 138 years of no major eruptions (>VEI 1–2), the question of what is occurring beneath the surface becomes especially poignant in the recent past. This work characterizes the mineralogy and geochemistry of the recent eruptive products of Cotopaxi, with emphasis on the two pulses of the 1877 eruption. Over the past 500 years Cotopaxi has had five major eruptive events (VEI 3–4), which occurred in 1532, 1742, 1744, 1768, and 1877, and included regional tephra fallout, pyroclastic scoria flows and surges, as well as lahars. After the initial pulse of the 1877 eruption and the subsequent lahars, a second pulse of magma produced pyroclastic density currents, containing scoria clasts up to 1 m in diameter. All samples collected from these eruptions are basaltic-andesite to andesite (56–59 wt % SiO 2), with a mineral assemblage composed of pl + opx + cpx + mag ± ol. Plagioclase from all samples range from An 47 to An 78 and show both normal and reverse zoning. Pyroxenes occur as augite and enstatite and do not exhibit significant zoning. The presence of disequilibrium textures such as zoned plagioclase and enclaves with fluidal margins with host indicate that magma mingling/mixing plays a role in magma genesis. The very similar petrologic characteristics of these deposits suggests that they were formed in a relatively long-lived magma system that experienced moderate differentiation and magma replenishment between eruptions. Fractional crystallization modeling shows that crystallization of plagioclase (11.7%) + pyroxene (3.4%) + amphibole (4.6%) + magnetite (1.1%) + apatite (0.2%) can produce the observed compositional variation. However, some of the variation can be explained by mixing, thus we conclude that both differentiation processes occurred. Thermobarometric data indicate that magma storage occurred at temperatures of ∼1017 °C and pressures ranging from 0.215 GPa (during the 1877 eruption) to 0.619 GPa (during the 1532 eruption), which is equivalent to depths of 7 and 21 km (±9 km), respectively. • Whole rock, glass, and mineral compositions for the five most recent eruptions. • New models of fractional crystallization to explain chemical variation. • Estimates of thermobarometry and magma storage conditions prior to eruption. [ABSTRACT FROM AUTHOR]

We use Intermediate-to-short wavelength (20–150 km) gravity anomalies to investigate the role played by crustal scale dense blocks in the genesis of Cu ore deposits along the Andes. These dense blocks are widespread along the margin and located at the fore-arc, arc, and back-arc domains, including depths in the range of 12–18 km, and thickness of 5–8 km. The interplay of these dense blocks with long-lived Trans-Lithospheric-Faults (TLF) controls the emplacement, and most likely, provides the required fertile fluids for the Cu ore genesis. Dense blocks represent impervious crustal domains, surrounded by damage zones at the intersection with TLF systems. Concentration of seismicity, large Vp/Vs ratios, low gravity domains, active volcanism, and structural fabric, demonstrate that these damage zones are in fact the most likely places for magma as well as mineralized flow ascent and emplacement. Basic flow models in porous media show a flow path that migrates horizontally at the base of dense/impervious blocks until the high permeability edge flanks, where pressure gradients provide the ideal conditions for the upward and focusing hydrothermal fluid ascent. Although not fully addressed in this paper, evidence suggests that the interaction of subducting-related fluids and the mafic-dense block might produce a fertile fluid with a concentration of Cu. In contrast with the long-standing view of metallogenic belts of the same age and parallel to the trench axis, we propose a multi-age metallogenic cluster, along the periphery of dense blocks, and organized oblique to the margin, following the trend of a given TLF. • Dense blocks and long-lived Trans-Lithospheric-Faults (TLF) control the emplacement and fertile fluids for Cu ore genesis. • Early Tectonic deformation dependence on crustal heterogeneities. • Multi age metallogenic belts following TLF systems. • Magmatic fluid flow migration depends on the crustal permeability, with flow path not-necessarily vertical. [ABSTRACT FROM AUTHOR]

The main objective of this study is to provide a review of the Tithonian succession of the Neuquén Basin and related Andean areas with an update from recent results on biostratigraphy and radio-isotopic geochronology. The studied successions include continental clastics and volcaniclastics of the Tordillo Formation and economically-important hydrocarbon source rocks such as the widespread black shales of the Vaca Muerta Formation, which has been ranked in recent studies as one of the most important recoverable shale oil and gas resources at global level. Significant recent data include the discovery of hyaline calpionellids associated with global nannofossil markers which are relevant to investigations of the definition of the Tithonian/Berriasian boundary. In addition, new high precision radio-isotopic data provide robust evidence to modify the absolute ages presently assigned to the base and top of the Tithonian Stage by the International Commission on Stratigraphy. • Updated review of the Tithonian of Andean Basins of Central Argentina and Chile. • Biostratigraphy combining ammonites, nannofossils, radiolarians and calpionellids. • High precision radio-isotopic CA-ID TIMS U-Pb zircon dating of ash fall tuffs. • Proposal for new absolute ages for the base and top of the Tithonian Stage. [ABSTRACT FROM AUTHOR]

Retroarc basins register the onset of compressional exhumation during the Cretaceous in the Andes, evidenced by sequences showing sedimentary provenance from the orogen. We present U–Pb detrital zircon geochronology from the Austral-Magallanes basin in the Southern Patagonian Andes (∼47–48°SL), where the foreland stage began in the Early Cretaceous. The littoral sandstones from basal foreland sequences of the Río Belgrano Formation yield ∼123 Ma maximum depositional ages, confirming previous studies that the basin infill is early Aptian. The detrital zircon ages showed two main clusters of 129-115 Ma and 151 -140 Ma, that are derived from the coetaneously exhumed Andean arc and earlier Jurassic magmatic sources. The zircons which overlap with ages of Upper Jurassic Andean synrift volcanics, confirms orogenic exhumation coeval with sedimentation. A sequence of retroarc volcanism dated between 119 and 97 Ma overlies the basal foreland littoral-continental deposits, and it is followed by a Late Cretaceous-Paleocene hiatus. Further analysis of detrital zircons ages distribution and geological considerations, indicates that the studied northern depocenter was a source region of sedimentary supply after its Cenomanian exhumation. • The northern depocenter of the Magallanes-Austral basin is characterized by Aptian-Albian regressive sequences. • U-Pb geochronology on detrital zircon registering a maximum depositional age for this sequence of 123 Ma. • U-Pb detrital ages between 151 and 140 Ma from Rio Belgrano Formation overlap with ages of Upper Jurassic synrift volcanic. • Exhumation of the synrift sequence allows us to interpret the onset of the uplift of the Patagonian Andes during the Aptian. • The construction of the Andes was diachronic throughout the Patagonia having a tendency to be younger to the south. [ABSTRACT FROM AUTHOR]

The deformation history of the Eastern Cordillera (EC) and Sub-Andean Zone (SAZ) of southern Peru is critical for understanding the roles that tectonics and climate played in the erosional exhumation of bedrock and the associated sediment flux delivered to the Amazon drainage basin. In this study, we report new field and subsurface data, apatite fission track (AFT) and (U–Th)/He thermochronological ages, U–Pb ages on detrital zircon grains, Sr–Nd isotopic compositions of fine sediments, which combined with previously published data, provide new constraints on the Neogene deformation and deposition history across the southern Peruvian EC and SAZ between 12° and 14°S. Late Miocene-Pliocene deformation is recorded by AFT and AHe ages in both the EC and SAZ and by growth strata geometry in the SAZ. This period is characterized by the development of piggy-back synclines and duplexes in the SAZ, overthrusting of the EC, and input of recycled sedimentary rocks of the SAZ and first cycle sediments from Triassic Plutonic rocks from the EC to the late Miocene-Pleistocene piggy-back syncline sediments. We report a transition from low-energy sand-dominated to high-energy conglomerate-dominated deposits in the Plio-Pleistocene marking an increase in sedimentation rates, indicating that the thrust wedge has continued to propagate. Our data agrees with that of previously published studies and indicate that the Late Miocene-Pliocene was a period of tectonic uplift and deformation in both the EC and SAZ. • Timing of Late Miocene-Pliocene uplift of the Eastern Cordillera and Sub Andean Zone constrained by AFT and AHe data. • Transition from a low to high energy fluvial system in the Late Miocene-Pliocene. • Provenance analysis of the Madre de Dios basin indicates Eastern Cordillera denudation and recycling of SAZ sediments. [ABSTRACT FROM AUTHOR]

Lanín is a composite volcano (∼39.38°S; 71.30°W) located in the Central Southern Volcanic Zone of the Andes. It is the southernmost member of the NW-SE volcanic alignment with the Villarrica and Quetrupillán composite volcanoes. During the Holocene, Lanín volcano erupted many lava flows, which we classify into three compositional groups: BAT (basalt, andesite, and basaltic trachyandesite), intermediate, and trachyte samples. The main recognised phenocrysts in the Lanín lavas are plagioclase, clinopyroxene, orthopyroxene, Fe–Ti oxides, and apatite. These mineral phases allow us to constrain the pre-eruptive (from the magma reservoir) conditions: temperature (985–1089 °C), pressure (1.8–4.1 kbar; equivalent to 6.5–15 km depth), and oxygen fugacity patch (∼QFM+0.4). In addition, textural features combined with pre-eruptive conditions suggest the existence of a crystal mush within the reservoir, which developed in two stages. The first stage considers the emplacement, crystal mush development, and eruption related to a melt of BAT composition. The residual melt evolved from BAT to trachytic primarily through fractional crystallisation. The second stage involves an evolved trachytic melt in the reservoir and the intrusion of a new, more mafic magma (presumably of BAT composition), which generates heating of the trachytic residual melt and crystal mush disaggregation. The fractional crystallisation also gives rise to scarce products of intermediate composition. This observation is consistent with the chemical constituents plots (TAS and Harker) and thermodynamic modelling. • During the Holocene, the products of the Lanín volcano range from basalt to trachyte. • We modelled the evolution from primitive to evolved compositions through fractional crystallisation. • The evolution occurred within a single highly crystalline reservoir. [ABSTRACT FROM AUTHOR]

The Andes offer a distinctive example of the intricate interplay among climate, tectonics, and surface processes. This is exemplified by the mountain range's north-south orientation, which contrasts with the prevailing east-west wind direction. This interplay controls the uplift evolution of the broken foreland and thus the sediment transfer and erosion from mountain ranges to their forelands. The Neuquén Andes is a peculiar segment of the southern Central Andes, registering dramatic North-South variabilities in elevation, climate, and tectonic intensities established during the Neogene and Quaternary. In this study, we aimed to identify the tectono-stratigraphic evidence of the Neogene to Quaternary evolution of paleo-environments and drainage networks in the intramountainous basin of Pampa de Agua Amarga in the broken foreland of the southern Neuquén Andes of Argentina. Starting with a non-depositional and/or erosional phase during the Paleogene, the Pampa de Agua Amarga Basin underwent several phases of syn-orogenic sedimentation in the late Oligocene to early Miocene. The basin gradually shifted from a lacustrine to an alluvial depositional environment, with alluvial deposits becoming dominant in the mid-Miocene and fluvial deposits dominating in the Pliocene. A significant event occurred during the late Pliocene to early Pleistocene when coarse fluvial deposits were deposited, marking the last aggradation phase. In the early Pleistocene, the onset of incision triggered the drainage system to cut through the downstream topographic barrier. The excavation of the basin was abrupt, as evidenced by a mid-Pleistocene stepped fluvial terrace and alluvial fan that filled a large canyon across the southern end of the downstream topographic barrier. The study confirms the regional trend that Miocene basin infill is related to dry climate and high tectonic uplift, which overwhelmed the erosive power of the drainage network. The lowering of tectonic uplift intensity in the southern Neuquén Basin during the Plio-Pleistocene, along with sudden fluctuations in the global colder and wetter climate, ultimately led to the excavation of the intramountainous basin. The Westerlies Wind Belts generate high precipitation rates in the southern Neuquén Andean Cordillera, feeding the Negro River catchment in the retroarc Andean broken foreland. Consequently, the erosive power of the Negro River catchment overcame the declining tectonic uplift, causing significant erosion of the entire broken foreland and Cordillera of the southern Neuquén Andes. Conversely, more intense tectonic uplifts in the northern Neuquén Andes built a more effective orographic barriers that limited precipitation rates of both the Westerlies Wind Belt and South America Summer Monsoon, and preserved the intramountainous basins and mountain interior from erosion. • Tectono-sedimentary analyze of an intramountainous basin in the South Neuquén Andes. • Neogene coarsening-up sequence due to a dry and warm climate and intense shortening. • Pleistocene basin excavation due to lower shortening and colder and wetter climate. • Pleistocene significant erosion and sedimentary transfer in the South Neuquén Andes. • Opposite tectonic, climate and thus basins' evolution in the North Neuquén Andes. [ABSTRACT FROM AUTHOR]

Abstract The southern Central Andes of Argentina and Chile (27–40°S) are the product of deformation, arc magmatism, and basin evolution above a long-lived subduction system. With sufficient timing and provenance constraints, Andean stratigraphic and structural records enable delineation of Mesozoic-Cenozoic variations in subsidence and tectonic regime. For the La Ramada Basin in the High Andes at ∼31–33°S, new assessments of provenance and depositional age provided by detrital zircon U-Pb geochronology help resolve deformational patterns and subsidence mechanisms over the past ∼200 Myr. Marine and nonmarine clastic deposits recorded the unroofing of basin margins and sediment contributions from the Andean magmatic arc during Late Triassic to Early Cretaceous extension, thermal subsidence, and possible slab rollback. Subsequent sediment delivery from the Coastal Cordillera corresponded with initial flexural accommodation in the La Ramada Basin during Andean shortening of late Early Cretaceous to Late Cretaceous age. The architecture of the foreland basin was influenced by the distribution of precursor extensional depocenters, suggesting that inherited basin geometries provided important controls on later flexural subsidence and basin evolution. Following latest Cretaceous to early Paleogene tectonic quiescence and a depositional hiatus, newly dated deposits in the western La Ramada Basin provide evidence for a late Paleogene episode of intra-arc and proximal retroarc extension (development of the Abanico Basin, principally in Chile, at ∼28–44°S). Inversion of this late Paleogene extensional basin system during Neogene compression indicates the southern Central Andes were produced by at least two punctuated episodes of shortening and uplift of Late Cretaceous and Neogene age. Highlights • Zircon U-Pb ages constrain provenance during Triassic–Paleogene basin evolution. • Extensional basin geometry influenced later thermal and flexural foreland subsidence. • Cretaceous–Neogene shortening was disrupted by neutral–extensional tectonic regimes. [ABSTRACT FROM AUTHOR]

Abstract The Gualcamayo Igneous Complex is located over the Pampean flat-slab segment (28–33°S), ∼110 km eastward from the Upper Miocene front arc position. It consists of subvolcanic rocks that are affected by porphyry-type hydrothermal alteration, and are genetically linked to a cluster of Carlin-type, skarn and epithermal gold deposits at the Gualcamayo mining district. The petrogenetic analysis of these volcanic rocks allows suggesting that this late Miocene (∼9 Ma) arc-related magmatism with an adakitic signature derives from asthenospheric mantle magmas that under thickened crust conditions, evolved through amphibole fractionation with lower crust melting, probably involving Grenvillian amphibolites from the basement of the Precordillera. These melts evolved towards shallower magma chambers, where they fractionated amphibole and plagioclase, leading to a variable adakitic signal. Graphical abstract Image 1 Highlights • The volcanic rocks of the Gualcamayo mining district represent the late Miocene (∼ 9 Ma) arc mineralizing magmatism ∼ 110 km eastward from the Upper Miocene front arc position. • They come from, hydrous and oxidized magmas with a variable adakite signature which is recognizable despite the hydrothermal alteration that affects these rocks. • The magmas that ultimately derived from an asthenospheric mantle evolved, under thickened crust through an amphibole fractionation with lower crust melting (wich probably involved Grenvillian amphibolites) complementing the high-pressure conditions. [ABSTRACT FROM AUTHOR]

The Catán Lil Basin is an intermontane basin developed on the wedge top of the Miocene North Patagonian retro-arc foreland basin. This basin is formed by the growth of a west verging thick skinned fold and thrust belt. An internal anticline divides the basin into two sub-basins: Las Coloradas and Los Remolinos, with other minor isolated depocentre (La Esperanza Syncline). Due to the structural configuration the basin evolved as a compartmentalized basin, connected with an extrabasinal drainage network. Structural and sedimentological analysis of field data enable us to determine that the basin was filled in four sequences (DS-I, DS-II, DS-III and DS-IV) that recorded three major aggradational/degradational cycles characterized by alluvial-fluvial sedimentation and a final volcanic succession of olivinic basalts. The first two sequences (DS-I and DS-II) integrate a growth wedge related to tectonic uplift and limb rotation of the main anticlines. DS-III and DS-IV were deposited under post-kinematic conditions when there was no more tectonic activity in the fold and thrust belt. There is a strong difference in composition between the first sequence DS-I and the others. DS-I is composed by volcaniclastic sandstones, conglomerates and paleosols. The two other sedimentary sequences (DS-II and DS-III) are composed of purely epiclastic material. This sedimentary succession can be defined as compound valley fill occurred under general low accommodation conditions with a progressive reduction of A/S during basin evolution. The DS-IV corresponds to a volcanic plateau associated with an upper Miocene basaltic retro-arc volcanism. A new 39 Ar/ 40 Ar age for the basalts is presented in this paper that constrains the end of deposition in the Catán Lil Basin to the Upper Miocene (8.5 Ma). After this basaltic event, the foreland turned towards an erosional by-pass system in the study area. [ABSTRACT FROM AUTHOR]

Astrogeodetic vertical deflections (VDs) are gravity field functionals which are independent from any other field observation such as gravity accelerations from gravimetry or geoid undulations from GPS and geometric levelling. They may be useful for the validation of global geopotential models or height transfer via GPS and astronomical levelling. VDs are sensitive to the local mass-distribution, so can be used in geophysical studies, too. Over Southern Hemisphere continents in general and South America in particular, VDs are exceptionally rare. This paper describes the reactivation of a unique VD data set that extends over parts of the Andes Mountains in Venezuela. The VD data was acquired 1983 and 1985 with classical astrogeodetic instrumentation at 24 field stations along a ∼80 km traverse crossing the Cordillera de Mérida with observation site elevations as high as ∼4500 m. To be compatible with modern geocentric gravity field products, the geodetic coordinates of the VD sites were transformed from the historic (non-geocentric) Venezuelan reference system to the geocentric ITRF2014, with residuals smaller than ∼1 m. In the ITRF, the measured VDs have RMS signal strengths of ∼20 arc-seconds (North-South) and ∼14 arc-seconds (East-West), with magnitudes exceeding 60 arc-seconds at one benchmark. The observed VDs were compared against VDs from GRACE, GOCE and EGM2008 data and from the ultra-high resolution GGMplus gravity maps. The GGMplus model was found to capture ∼85 to 90% (in terms of root-mean-square signals) of the measured VD signals. Both VD components are in ∼2 arc-sec agreement with GGMplus. Overall, the agreement between observed VDs and modelled VDs is considered satisfactory, given the VDs were measured in a topographically rugged region, where residual signals may be large and global models are not well supported through regional terrestrial gravity data. The VDs may be useful, e.g., for the assessment of high-frequency constituents of present and future high-degree gravitational models (e.g., EGM2020) and calibration of model commission errors. The Venezuelan VD data is freely available. [ABSTRACT FROM AUTHOR]

The response of sedimentary basins to earliest onset of Andean contraction and lithospheric flexure in the southern Central Andes is debated and not well-resolved. The Upper Cretaceous to Oligocene strata of the Cuesta de Huaco anticline in the Argentine Precordillera record sedimentation, regional deformation, and climate patterns prior to the highly studied Oligocene-Miocene foreland basin phase. These deposits have recently been recognized as Cretaceous and Paleogene in age, prompting a re-evaluation of this depocenter as part of the early Andean system, prior to deposition of the aeolian foredeep sediments of the Oligocene Vallecito Formation. This work presents new data from the Argentine Precordillera fold-and-thrust belt at 30°S that sheds light on new reinterpretations of the timing of sedimentation for an important interval in Andean retroarc foreland basin history. We report the first Paleocene detrital radiometric ages from the Cuesta de Huaco ‘red strata’ of the pre-Oligocene Bermejo Basin. Detailed sedimentology and provenance data from the Cenomanian-Turonian Ciénaga del Río Huaco and Danian-Priabonian Puesto La Flecha formations reveal a Cenomanian-Turonian braided stream system that transitioned into a shallow freshwater lacustrine depocenter in Paleocene-Eocene time. During Late Cretaceous time, sediment in the braided river system was derived primarily from northeastern cratonic sources; during the Paleocene-Eocene, uplift and unroofing of the Andean arc and Frontal Cordillera resulted in an influx of western-derived sediment. We therefore suggest a revised timing of sedimentation for the transition to Andean retroarc foreland basin deposition. [ABSTRACT FROM AUTHOR]

The comments by Kietzmann & Iglesia Llanos (Comment on “Tethyan calpionellids in the Neuquén Basin (Argentine Andes), their significance in defining the Jurassic/Cretaceous boundary and pathways for Tethyan-Eastern Pacific connections” by R. López-Martínez, B. Aguirre-Urreta, M. Lescano, A. Concheyro, V. Vennari and V. Ramos) on our paper published in the Journal of South American Earth Sciences 78 (2017): 116-125, provide a worthy opportunity to further clarify our observations and interpretations regarding the importance of precise biostratigraphic studies in the definition of the Jurassic/Cretaceous boundary in the Argentine Andes. These include the calpionellids as primary markers, the classic and widespread nannofossils bioevents as secondary markers, together with a detailed ammonite zonation. [ABSTRACT FROM AUTHOR]

Paniri volcano, in northern Chile, belongs to a volcanic chain trending across the main orientation of the Central Andean volcanic province. Field work mapping, stratigraphic sequences, and one new 40 Ar/ 39 Ar and eleven previous published 40 Ar/ 39 Ar, and K/Ar ages, indicate that the evolution of Paniri involved eruption of seven volcanic units (Malku, Los Gordos, Las Lenguas, Las Negras, Viscacha, Laguna, and Llareta) during four main stages occurring over more than 1 Myr: Plateau Shield (>800 ka); Main Edifice (800–400 ka); Old Cone (400–250 ka); and New Cone (250–100 ka). Considering glacial and fluvial action, an estimated 85.3 km 3 of volcanic material were erupted during the eruptive history of Paniri volcano, giving a bulk eruption rate of 0.061 km 3 /ka, with major activity in the last 150 kyr (eruption rate of 0.101 km 3 /ka). Lava flows from Paniri show abundant plagioclase together with subordinate ortho-, and clino-pyroxene, and amphibole as main phenocrysts. Moreover, although true basalts are scarce in the Central Andes, olivine-bearing lavas were erupted at Paniri at ∼400 ka. Also, scarce phenocrysts of biotite, quartz, rutile, and opaque minerals (Fe-Ti oxides) were identified. The groundmass of these flows is composed mainly of glass along with pyroxene and plagioclase microlites. Consolidated and unconsolidated pyroclastic deposits of dacitic composition are also present. The consolidated deposits correspond to vitreous tuffs, whilst unconsolidated deposits are composed of pumice clasts up to 5 cm in diameter. Both pyroclastic deposits are composed of glassy groundmass (up to 80% vol.), and subordinated plagioclase, hornblende, and biotite phenocrysts up to 1 cm in length. Results of twenty-four new, coupled with previous published compositional analyses show that volcanic products of Paniri vary from 57% (basaltic-andesite) to 71% (rhyolite) vol. SiO 2 , with significant linear correlations between major element-oxide and trace-element concentrations. 87 Sr/ 86 Sr isotope ratios range from 0.7070 to 0.7075, indicating that Paniri, similar to other volcanoes of the San Pedro – Linzor volcanic chain, have undergone significant crustal contamination of its parental magmas. However, the almost constant Sr-isotope compositions of the different volcanic units defined for Paniri volcano, suggested later fractional crystallization of magmas at upper crustal levels. [ABSTRACT FROM AUTHOR]

In this study, I integrated geochemical modeling and receiver functions to test for magmatic fractionation above a garnet pyroxenite arc root structure beneath the Colombian magmatic arc (Northern Andes), as a feasible mechanism to explain the record of steep rare earth element (REE) patterns in modern volcanism and the development of an amphibole-rich middle to lower crust. Magmatic fractionation was evaluated through the geochemical modeling of volcanic rocks that show steep REE patterns with high Sr/Y and La/Yb ratios. A well-defined REE geochemical trend was accomplished for all samples at temperature and pressure estimates that are consistent with middle to lower crustal conditions (∼825-935 °C, ∼10.0–14.7 kbar). From the integration of receiver functions, after analyzing the middle to lower crustal signals at multiple stations on top of active volcanoes, the deep crust of the arc is interpreted as a seismically fast (Vs: ≥4.5 km/s) and dense arc root (≥3.3 g/cm3), above which, lies a low-velocity zone with a horizontal to tilted anisotropy axis. This anisotropic low-velocity region is proposed as a partially molten domain related to the evolution of the arc system. The proposed magmatic fractionating model explains satisfactorily the genesis of rocks with steep REE patterns and high Sr/Y (>40) and La/Yb (>20) ratios as a counterpart for a clinopyroxene amphibolite residuum composing deep levels of the arc crust. I suggest that these fractionating processes are playing an important role in the construction of the Colombian magmatic arc, enabling the formation of a dense garnet pyroxenite arc root, a genetically related amphibole-rich middle to lower crust, and the derivation of steep REE patterns with high Sr/Y and La/Yb ratios in the modern Colombian volcanism. • New constraints on the related genesis of the amphibole-rich lower crust and volcanism with steep REE patterns along the Colombian arc, Northern Andes, through integrated whole-rock geochemical modeling and receiver function analysis. • Magmatic fractionation modeling retrieved temperature and pressure estimates consistent with the middle to lower crust and explains the genesis of rocks showing steep REE patterns with high Sr/Y and La/Yb ratios as a counterpart for a clinopyroxene amphibolite residuum in the deep crust. • The lower crustal receiver function signal reconciles with a seismically fast and dense arc root, above which, lies a deep anisotropic low-velocity zone, interpreted as a partially molten region linked to the magmatic fractionating system. [ABSTRACT FROM AUTHOR]

We present here the longest known continuous annual moraine record extending from the XVIII century to the present, which portrays a very irregular retreat history of the tropical Tarija Glacier, in the Bolivian Andes. This study also proves for the first time in South America, the annual formation on these minor moraines, while field observations showed how these ridges form, substantiating the presented 258 year-long glacial retreat history. The annual retreat record is validated by correlation with Lake Titicaca surface level evolution: the highest ablation rate matches the highest lake level (1986–1987 yr). The glacial retreat also fits well with a large Pampean foreland lake level evolution (Mar Chiquita), suggesting this glacier reflects continental-scale climate trends. There is, however, no correlation with CO 2 concentration curves. The glacier retreat suggest there were at least seven events of warming that lasted one to two decades, and none of these had any correlation to the greenhose gasses evolution. Besides, glacier retreat slowed down over the last three decades, in coincidence with the tendency of large lakes to a level fall, suggesting warming rate would also slow down. The departure of the glacial retreat chronology that worldwide is considered to be related to warming, from the CO 2 evolution over the last three centuries, suggests CO 2 does not contribute a primary effect on warming, as most models assume. Given some coincidences, we suggest climate shifts causing the irregular retreat of the Tarija Glacier, may be related to a delayed effect of solar irradiance indicating that the relation between solar irradiance and its impact on Earth's surface systems needs to be better understood for a critical examination of the climate change paradigm. • The Tarija Glacier retreat rate was unsteady, defining eight warming cycles over the last three centuries. • The fastest retreat was observed near 1987 and after 1990, a slower glacier retreat suggest temperature was cooler. • The correlation of Tarija glacier retreat rate changes and large south American lake levels, suggest changes detected were of continental-scale. • The departure between glacier behaviour and CO 2 evolution suggest greenhouse gasses effect on warming is minor or absent. • Glacier retreat changes defining warming periods correlate with solar irradiance peaks but with c. Two decades of delay. [ABSTRACT FROM AUTHOR]

The southern Ecuadorian forearc system is related to the subduction of the oceanic Farallon/Nazca Plate beneath the continental South American Plate since the Late Cretaceous, and currently evolves with the dynamic of a tectonic block called North Andean Sliver. To explore the structural architecture and processes controlling the Upper Cretaceous-Cenozoic growth of the forearc, we built a ∼143 km-long onshore-offshore crustal-scale cross-section in the Santa Elena Peninsula region using seismic reflection profiles and well and field data. The structure of the Santa Elena Peninsula forearc system is controlled by imbrication of Upper Cretaceous-Palaeocene oceanic basement and Cenozoic sedimentary units, and underplating of distal Cenozoic sequences stacked at the trench zone. This led to the progressive construction of an accretionary wedge through time. The forearc substratum is mainly formed by the Upper Cretaceous-Palaeocene basement developed during the docking of oceanic terranes. It is later deformed by NW-trending landward-dipping, normal to strike-slip faults during the Middle Eocene, and renewed compression by inversion of inherited faults from the Oligocene onwards. Recent deformation consists in N-trending oceanward-dipping normal faults in the frontal slope domain and fault-controlled uplift of marine terraces along the coastal area. Therefore, the Upper Cretaceous to present-day structural evolution of the Santa Elena Peninsula forearc is controlled by the long-lasting subduction dynamics and structural inheritance of the upper plate. • We illustrate the structural architecture of the Santa Elena Peninsula forearc system. • It is dominated by compression punctuated by zones/episodes of normal to strike-slip faulting. • Its evolution reflects the subduction dynamics and the upper plate structural inheritance. [ABSTRACT FROM AUTHOR]

Phosphate rock occurrences in western Venezuela are well-known in Cretaceous sedimentary sequences, which are associated to the Caribbean-Tethyan passive margin, along an SW-trend belt of the Venezuelan Andes chain. In this study, the geochemical characteristics of the Navay phosphate deposit were investigated to discuss the ocean paleo-oceanographic conditions and diagenetic controls that prevailed during the deposit formation. The rare earth elements plus yttrium (REY) concentrations were determined and normalized with the Post-Archean Australian Shale (PAAS) values to generate the REY patterns. Our results reveal a typical seawater signature, except for the absence of a marked negative Ce* anomaly (Ce/Ce* = 0.76–1.00). The determined seawater REY patterns, along to the calculated ratios for (La/Sm) N = 0.78–1.00, and (La/Yb) N = 0.34–0.66, are similar to the modern oceanic water ratios. These data point to a lack of diagenetic alteration on the primary REY signatures, which corresponds with a terrigenous-free marine sediment source for the REY content present in the deposit. In brief: i) the slightly negative anomalies displayed by the Ce* and Eu*, accompanied by the Mn depletion, ii) a relative enrichment of some transition metal elements (V, Cr, and Cu), and iii) the low Mo/U ratios, are all of them considered as geochemical indicators of suboxic to anoxic conditions, which were predominated during the phosphogenetic processes of the deposit. Furthermore, our data reveals an economic potential of the phosphorites as a raw material to produce phosphoric acid (H 3 PO 4) as well as a source of supply for rare earth elements, by means of: i) relative high grades of P 2 O 5 (15.46–30.09 wt %), ii) low CaO/P 2 O 5 ratios (1.22–1.28), iii) a lack of organic matter, chert or chalcedony, iv) a low content of Mg (0.07–0.22%), v) REE concentrations varying from 141.82 to 256.53 μg/g, with an average value of 208.14 μg/g; and vi) concentrations for toxic elements (i.e., V, Cr, Co, Ni, Cu, Zn, As, Sr, Pb, and U) below or at the acceptable levels, in comparison to commercial phosphorites worldwide. • Navay phosphorites can be considered raw materials to produce phosphoric acid. • Navay phosphorites can be a strategic source of supply of rare earth elements. • Concentrations of "potentially toxic elements" are below or at acceptable levels compared to commercial phosphorites worldwide. • Geochemical signatures suggest suboxic to anoxic conditions during phosphogenic processes of the deposit. [ABSTRACT FROM AUTHOR]

The Andes orogenic belt is one of the most tectonically active zones located between the convergent margins of the South American plate and the Pacific plate. From the dissected western belt to the expanded alluvial plain of Amazon basin, the Madeira watershed bears recent tectonic imprints. The tectonic signature is well documented by the spatial and linear characteristics of the five sub watersheds along with the Madeira trunk river and channels. The level of tectonic activeness has been assessed on the sub watersheds of the Madeira River, which is one of the main right-hand tributaries of the Amazon River. On the five defined sub-watersheds and the main channel watershed of Madeira, several morphometric indices, viz., asymmetry factor (AF), tilt angle (β), sinuosity index (SI), channel concavity (ɵ), elongation ratio (Re), circularity ratio (Rc), transverse topographic symmetry factor (T) and basin shape index (Bs), have been used. To rank the watersheds based on tectonic activity, we applied the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) The active tectonics was also tested by a comparative study of linear indicators as Hack profiles, longitudinal profiles and segment-wise stream gradient index (SL) of watersheds 2 (rank 1) and 3 (rank 6). The results reveal that the most tectonically active watershed 2 is located in a high seismic magnitude zone with several deep earthquake epicenters. The least tectonically active watershed 6 is located in a low seismic zone. • SpAtial and linear-scale morphometry of Madeira watershed performed. • Through TOPSIS model and tectonic prioritization rank, zones of more active tectonics identified. • A comparative analysis of the river profiles of the tectonically most and least active rivers has been carried out. • Seismic set up of the region has been studied. [ABSTRACT FROM AUTHOR]

The Bermejo retroarc foreland basin system formed in flexural response to Cenozoic crustal thickening in the Andean orogenic system, specifically, the eastward propagation of the Precordillera fold-thrust belt and the basement-involved uplift of the Sierras Pampeanas. Previous work in the region has mainly focused on the mechanisms and expression of flat slab subduction and the structural geometry of the basement-involved Sierras Pampeanas and east-directed Precordillera fold-thrust belt at depth, advancing our understanding of the Bermejo basin history north of 31°S. However, the along strike evolution of the basin system to the south remains unresolved and contrasting tectonic models have proposed the Bermejo basin evolved synchronously versus asynchronously through time. Our study seeks to constrain the along-strike Neogene tectonics of the Bermejo basin via well-exposed Miocene fluvial stratigraphic intervals along the Eastern Precordillera, integrated with detrital zircon U–Pb geochronology provenance and detrital apatite (U–Th)/He thermochronology datasets. New data from two Neogene stratigraphic sections in the southern Bermejo basin constrain deposition between 13 and 6 Ma. Dominant fluvial-lacustrine mudstones, siltstones, and sandstones transition into fluvial-megafan deposits capped by alluvial fan conglomerate facies, tracking the eastward migration of Precordillera deformation. The cessation of sedimentation, and thermal history models of apatite (U–Th-Sm)/He thermochronology ages, indicates basin incorporation into the orogenic wedge by 6 Ma. When we compare our southern datasets with previous constraints from the northern Bermejo basin, we observe, from north to south: (1) a time-transgressive trend in basin initiation, (2) a ∼3 km decrease in stratigraphic thicknesses, and (3) older exhumation along the thrust front. These trends highlight the asynchronous nature of the Bermejo foreland basin system and along-strike variability of Precordillera thrust-front evolution. • New measured stratigraphic sections from the southern Bermejo basin are compared against localities along-strike • Detrital zircon U–Pb ages constrain deposition between 13 and 6 Ma, and record erosion of Andean source regions • Detrital apatite He dates track basin burial reheating, and cooling during exhumation of the Eastern Precordillera • Time-transgressive trend in exhumation along strike of the Bermejo basin implies diachronous deformation of basin deposits [ABSTRACT FROM AUTHOR]

Cetina et al. (2019) presented new geochronological, geochemical and isotopic data obtained from volcanic and sub-volcanic rocks exposed in the northern segment of the Western Cordillera of Colombia, which are interpreted as related to a Cretaceous island arc-plateau system. These data are used to come up with a paleogeographic model for the circum-Caribbean realm that may account for the presence of old (Paleozoic – Proterozoic) xenocrystic zircons in the analyzed units. Nevertheless, the authors ignored previously published geological, geochemical, geochronological, thermochronological and provenance constraints from Cretaceous rocks of northwestern Colombia, which refuse the plausibility of their proposed models. Particularly, the occurrence of Cretaceous subduction-related metamorphism, magmatism and construction of marginal sedimentary basins, documented by several published papers in the last decade, renders the paleogeographic reconstructions of Cetina et al. (2019) to be unlikely. We demonstrate that when considering the ignored geological evidences, alternative explanations for the origin of pre-Mesozoic xenocrystic zircons are required. • We comment the recently published paper by Cetina et al. (2019). • Several ignored geological evidences are recalled and discussed. • Paleogeographic models of Cetina et al. (2019) are not plausible. • Alternative explanations for the origin of pre-Mesozoic xenocrystic zircons are required. [ABSTRACT FROM AUTHOR]

Extensive fieldwork at the Cotacachi-Cuicocha Volcanic Complex (CCVC, North of Ecuador) resulted in a new collection of geological data including cartography, chronology, petrography, geochemistry, and morphology. This volcanic complex is formed by a central volcano (Cotacachi: 4939 m asl, current bulk volume of 56 ± 4 km3), several peripheral domes, and a 3 km wide volcanic caldera (Cuicocha: 4.2 ± 0.1 km3). CCVC comprises three stratigraphic members: The first, Cotacachi Basal, represents the initial phase of construction, which started at 173 ± 4 ka with a basal andesitic lava flow succession (∼500 m-thick) including isolated basaltic-andesitic lavas (Verde Tola unit; NE: 113 ± 6 ka, SE: 133 ± 9 ka), the construction of some peripheral amphibole-bearing andesitic domes, such as Muyurcu and Loma Negra (138 ± 4 ka and <108 ka, respectively), and a debris-avalanche deposit to the north-west (0.5–1.8 km3, older than 108 ka). The second member, Upper Cotacachi, consists of an andesitic lava flow succession (∼300 m-thick), younger than 108 ± 6 ka. A gap of activity occurred afterwards from 100 to 70 ka, during which a second debris-avalanche (0.2–1.1 km3, 108 to 65 ka) occurred to the NE, followed by the effusion of the dacitic Piribuela dome (65 ± 2 ka). Afterwards, several superimposed andesitic lava flows were emplaced at the summit, possibly around 15–10 ka since they lack glacial erosion. The third member includes the extrusion of the andesitic Cuicocha pre-caldera domes, which marks the beginning of a new eruptive stage of activity of CCVC during the Holocene, resulting in a violent eruption (3525 ± 35 to 2980 ± 30 a BP; VEI = 5) that partially destroyed the young dome and formed a funnel-shaped caldera (Cuicocha Caldera-Lake), ending with the emplacement of the Wolf and Yerovi post-caldera domes. • Geologic study of a younger but largest volcano in the northern Andes of Ecuador. • Reconstruction of Cotacachi Cuicocha Volcanic Complex evolution. • Overview of a caldera-forming event (VEI 5) of Cuicocha during Holocene (2980 a BP). [ABSTRACT FROM AUTHOR]

Andean fold-and-thrust belts (FTBs) in the western border of South America show important along-strike variations in their structural style (thin- or thick-skinned) and shortening magnitudes, among others. These variations can arise from multiple factors, such as depth-to-detachment, geometry, and thickness of underlying basins, structural highs, the competence of the units involved in deformation, pre-orogenic structure of the basement, the rheological state of the upper crust or latitudinal gradients in shortening, among others. We carry out a set of new analogue models to understand how two of these factors affect the development and the geometry of the thrust systems within the Andean Principal Cordillera and adjacent fold-and-thrust belts at 32°-34°S (La Ramada and Aconcagua FTBs). In this contribution, we present the results of analogue modeling of doubly-vergent thrust systems with a built-in heterogeneity that allow us to evaluate the influence of differential shortening and presence of competent blocks (of relatively higher cohesion) in the generation, evolution, and structural setting of Andean FTBs. We highlight that despite the similar pattern of differential shortening in the models, the presence of the competent block has a significant influence on the structural configuration and leads to greater topographic uplift. Differential shortening plays a role in accommodating deformation, but when a competent block is present, the faults bounding the block control the deformation, producing a notable curvature of the FTBs. Summarizing, the presence of a competent block significantly influences the structural configuration within a doubly-vergent thrust system, emphasizing the role of inherited architecture in the orogenic growth of the Southern Central Andes. • Analogue models were carried out to assess the impact of differential shortening and competent blocks on FTB formation. • We ran a series of models to establish comparisons with the Principal Cordillera and neighboring FTBs in the Central Andes. • We recognize that pre-orogenic architecture controls the structural development of the Southern Central Andes. • We recognize that competent blocks within a doubly-vergent wedge induces the generation of curved thrust systems. • We propose that differential shortening and competent blocks exert critical control on obliquity andmcurvatures of structures. [ABSTRACT FROM AUTHOR]

The Eocene and Oligocene deposits of the southwestern region of the Sinú-San Jacinto Belt (SSJB) in NW South America were formed in marine environments influenced by fluvial discharges from the northern Andes of Colombia. However, these deposits are not well-exposed on the surface, which has limited the study of micropaleontological assemblages that could improve our understanding of the chronostratigraphic and paleoenvironmental characteristics of these rocks. In this study, we analyzed two cores of one of the thickest Cenozoic stratigraphic sections in the Caribbean region, from the ANH-TIERRALTA-2-X-P stratigraphic well, using palynomorphs and calcareous nannofossils. Our analysis allowed us to determine the age of deposition and understand the biostratigraphic patterns of marine and terrestrial microfossils in these nearshore deposits. We found that the first cored interval, from 2122 m to 2026.9 m, corresponds to marine rocks accumulated between the middle and late Eocene. The second interval, from 1130 m to 731.6 m, showed patterns of terrestrial and marine microfossils, which indicate the middle-late Eocene to the Early Miocene age. Palynological and calcareous nannofossil biostratigraphy were consistent in the middle to upper Eocene and Lower Miocene deposits, but discrepancies were observed in the Oligocene deposits. We attributed this to reworking or broader biostratigraphic ranges of certain palynological markers used in the biozones. Determining the age of the middle to upper Eocene and upper Eocene to lower Oligocene deposits was challenging due to the limited number of well-calibrated biostratigraphic markers. As a result, accurate correlation with the late Eocene – early Oligocene stratigraphic record from other parts of the SSJB is hindered, demonstrating that regional stratigraphic correlations based on biostratigraphy alone are problematic. • Middle-upper Eocene to Lower Miocene deposits of the ANH-TIERRALTA-2-X-P stratigraphic well of the Sinú-San Jacinto Belt. • Integrated palynomorph and calcareous nannofossil biostratigraphy of Colombian Caribbean region. • Integrated biostratigraphic age model of the ANH-TIERRALTA-2-X-P. • Biostratigraphic patterns of terrestrial and marine microfossils in fluvio-deltaic deposits. [ABSTRACT FROM AUTHOR]

The geomorphometric classifications of three groups of volcanoes situated in the Andes Cordillera, Central America, and Mexico are performed and compared. Input data are eight local topographic gradients (i.e. elevation differences) obtained by processing each volcano raster ASTER-GDEM data. The pixels of each volcano DEM have been classified into 17 classes through a K- means clustering procedure following principal component analysis of the gradients. The spatial distribution of the classes, representing homogeneous terrain units, is shown on thematic colour maps, where colours are assigned according to mean slope and aspect class values. The interpretation of the geomorphometric classification of the volcanoes is based on the statistics of both gradients and morphometric parameters (slope, aspect and elevation). The latter were used for a comparison of the volcanoes, performed through classes’ slope/aspect scatterplots and multidimensional methods. In this paper, we apply the mentioned methodology on 21 volcanoes, randomly chosen from Mexico to Patagonia, to show how it may contribute to detect geomorphological similarities and differences among them. As such, both its descriptive and graphical abilities may be a useful complement to future volcanological studies. [ABSTRACT FROM AUTHOR]

Previous geologic studies and structural interpretations of the Meso-Cenozoic units in the Andean Principal Cordillera, between 32°- 33°S, have faced many difficulties due to the strong variability in volcanic deposits' thickness, the structural complexity that affects the involved units, and the scarcity of geochronological data that prevents defining a clear boundary between them. Structural-lithologic work carried out between 32°45′-33°S allowed us to recognize and define 4 different lithologic units along the Aconcagua-Juncal river valleys: one marine sedimentary unit assigned to the Cretaceous Mendoza Group and Late Jurassic exposures from the Río Damas/Tordillo Formation, and 3 volcano-sedimentary units mainly associated with Cenozoic volcanism represented by the Farellones, Abanico, and Cristo Redentor formations. The stratigraphic-structural model proposed in this work also allows for defining 3 structural domains throughout the study area: a western domain close to the Pocuro Fault Zone, a central domain, and an eastern domain close to the Alto del Juncal Fault Zone, next to the Chile-Argentina international border. The western and central domains show folds with larger wavelengths than the eastern domain, while the eastern domain shows intense deformation related to the emplacement and evolution of the Aconcagua fold and thrust belt. This deformation results from tectonic events which mainly occurred between the Upper Oligocene and Miocene. In the study region, these events caused a minimum shortening of ∼30 km in the Principal Cordillera. Based on the collected information, the Alto del Juncal Fault is also interpreted as the eastern Abanico basin bounding fault in which the Aconcagua fold-thrust belt is rooted. • We perform a stratigraphical and structural mapping at the Principal Andes between 32°45′ and 33°S. • We recognize and define 4 different lithologic units along the Aconcagua-Juncal river valleys. • We recognize and define 3 structural domains throughout the study area. • We propose the Alto del Juncal Fault as the eastern Abanico basin bounding fault in which the AFTB belt is rooted. • A tentative evolution of the studied region from the late Eocene to the late Pliocene is presented. [ABSTRACT FROM AUTHOR]

The youngest and best exposed Iron Oxide Cu–Au (IOCG) deposits currently recognized are found in the coastal belt of the Andes. Their formation has been attributed to back-arc extension or transtension associated with the convergent Andean margin. Here we document transpressional deformation synchronous with Cu mineralization in the Candelaria-Punta del Cobre district, the largest IOCG district of the Andean belt. A northwest-southeast shortening direction is recorded by north-northwest sinistral strike-slip faults that host mineralization, northwest dikes, and north-northeast compressive structures. Batholith emplacement synchronous with mineralization formed a north-northeast oriented foliation zone parallel to the intrusive contact and associated folds in the host rock sequences that face inwards towards the intrusive contact. Age constraints indicate that transpressional deformation in the Cretaceous arc, at least locally, begun earlier than previously documented, and IOCG mineralization may have spanned the transition from extension to the initial phase of compression. [ABSTRACT FROM AUTHOR]

Even though the first oil field of Venezuela (La petrólia, 1883) was discovered in the Táchira Depression, located at the junction of the Venezuelan Andes with the Cordillera Oriental of Colombia, no liquid hydrocarbon discoveries have been made in the area ever since. However, there are extensive asphalt accumulations impregnating Mio-Pliocene conglomerates, which have been exploited intermittently mostly for road construction. These asphalt accumulations occur in the central eastern portion of the Táchira Depression in the basal part of fluvial conglomerates of the La Copé Fm. that were deposited uncomfortably on top of Cenozoic and Cretaceous rocks. These sediments were sourced and deposited unconformably on the nose and flanks of a large-scale anticline oriented N40° and plunging to the SW (Uribante High) product of the first phase of the Andean orogeny. The conglomerates located on the western part of this high were charged with oil derived from the Cretaceous La Luna Formation that was generating at the time of deposition of the unit. This oil migrated into the conglomerates and moved updip until they became trapped in a major stratigraphic accumulation. The seals of the accumulation were formed by lateral facies changes, overbank shales, or eventually the muddier Upper Member of the La Copé Fm. It is postulated that this stratigraphic trap was later deformed, uplifted and partially eroded, with the asphalt impregnations being the remnants of this paleo-accumulation and not present-day oil seeps as previously postulated. A rough estimate of the total hydrocarbons in place in the outcrops of the La Copé Fm is in the order of 100 MMBO, however the original accumulation was orders of magnitude larger. Since the bridged regional high was the focus of charge in the basin during the peak of oil generation in the Táchira Depression, it is believed that a large portion of the hydrocarbons generated were lost, which may explain the lack of significant discoveries in the area. [ABSTRACT FROM AUTHOR]

A >15-20 km-thick succession in southern Bolivia forms the most-complete stratigraphic record in western Gondwana. Upper Neoproterozoic–Carboniferous clastic rocks record ∼300 Myr of marine, nonmarine, and glacially influenced sedimentation in diverse basin systems generated by variable tectonic regimes along the western edge of Gondwana during active and passive-margin conditions. New provenance results help resolve key uncertainties regarding source regions and sediment dispersal patterns. The findings are integrated with spatial variations in stratigraphic thicknesses to evaluate regional patterns of basin subsidence, magmatism, and deformation during long-term evolution of the western Gondwanan margin in the central Andes. Detrital zircon U–Pb geochronological data for 17 sandstone samples reveal sedimentary input from Precambrian cratonic basement provinces and pre-Andean basement, magmatic arc, and fold-thrust belt source regions. The basement age signatures indicate derivation from the flanking Brasiliano (900-560 Ma) and Pampean (650-500 Ma) provinces to the south and east, and the distal Rio de la Plata craton (2400-2000 Ma) along the eastern South American margin ∼1000–1500 km to the southeast. Although the greater Amazonian craton was not a major contributor, subordinate Amazonian signatures from the Sunsás (1300-950 Ma) province to the east and northeast selectively fed the northern basin regions of the central Andes. Despite the lack of Paleozoic igneous rocks in Bolivia, detrital zircons of Ordovician age attest to the pre-Andean influence of the subduction-related Famatinian magmatic arc. Limited Devonian-Carboniferous igneous material was contributed locally from western pre-Andean highlands or regionally by axial northward transport from selected igneous sources in Argentina and Chile. Episodic recycling of Neoproterozoic–Paleozoic basin fill, including a sharp reappearance of Famatinian-age detritus, can be linked to periods of Paleozoic crustal shortening and foreland sedimentation ascribed to Famatinian, Ocloyic, Chañic, or Gondwanide phases of deformation. The spatial distribution of sediment sources along with temporal shifts in sediment routing highlight several stages in the paleogeographic evolution of the western Gondwanan margin preserved in the central Andes. Initial regional subsidence spanned a multiphase Neoproterozoic to early Paleozoic history of Rodinia breakup, Brasiliano-Pampean orogenesis, and post-orogenic back-arc extension prior to final late Paleozoic amalgamation of Gondwana. The early Paleozoic onset of subduction and Famatinian arc magmatism led to high-magnitude subsidence (>10–15 km) likely driven by Ordovician slab rollback in an extensional back-arc basin. Thereafter, intermittent Paleozoic contraction in a poorly understood pre-Andean system (best expressed in the Eastern Cordillera of Bolivia and neighboring segments of northern Argentina and southern Peru) generated transient topographic loads that produced superimposed flexural foreland and successor basin systems. • Southern Bolivia contains the most-complete stratigraphic record of western Gondwana. • Detrital zircon U-Pb ages reveal Neoproterozoic-Paleozoic shifts in sediment sources. • Proximal and distal (>1000 km) cratonic sources fed pre-Andean sedimentary basins. • Slab rollback in a back-arc basin likely caused >10 km of Ordovician subsidence. • Cratonic and Famatinian arc/orogenic sources fed Paleozoic foreland/successor basins. [ABSTRACT FROM AUTHOR]