Search

The historic Quadrilátero Ferrífero mining district in Brazil is a polydeformed Archean terrane recording several tectonic events. This history has hampered the accurate dating of its important gold deposits, given that most of the geochronological clocks have been affected by multiple thermal events. To determine an accurate time constraint for the mineralizing events in this region, we provide the first Re-Os dating for a gold deposit in the Quadrilátero Ferrífero, obtained from 13 mineral separates of disseminated sulfide phases (pyrrhotite, coarse-grained arsenopyrite, fine-grained arsenopyrite, and pyrite) at the recently discovered São Sebastião deposit (northwest Quadrilátero Ferrífero). Three distinct successive sulfidation stages are interpreted at the deposit. The final stage, texturally associated with gold, is marked by fine-grained arsenopyrite and pyrite (assemblage III) and is associated with high-temperature (~600°C) features. A Re-Os errorchron is obtained when considering the data of all samples collectively; however, a comprehensive Re-Os isochron age of 1987 ± 72 Ma (2σ; n = 4; IsoplotR model 3; initial 187Os/188Os = 2.1 ± 0.7) is obtained from assemblage III. A 187Re-187Osr isochron at 1988 ± 56 Ma (mean square of weighted deviates = 0.1, initial 187Osr = –0.1 ± 2.6 ppt; n = 4) is obtained if an initial 187Os/188Os composition of ca. 2.1, is used, this being consistent with the fact that the 187Os in the sulfides in assemblage III is largely radiogenic (187Osr). Earlier assemblages (I and II) individually show variable initial 187Os/188Os, indicative of disturbance to the Re-Os systematics at ~2.0 Ga. This age is considered the best estimate for the timing of gold mineralization at São Sebastião, being coincident with the waning stages of the Minas orogeny, the thermal effects of which are restricted to the southern Quadrilátero Ferrífero. Hence, we consider that the hot fluids from which assemblage III crystallized were responsible for resetting the Re-Os systematics in assemblages I and II and were central to Paleoproterozoic gold deposition in the region. This ~2.0 Ga age challenges previous notions of a late Archean, ~2.7 Ga mineralizing event in the Quadrilátero Ferrífero and makes it possible that gold remobilization occurred elsewhere in the region, particularly in areas representing deeper crustal levels.

—The Kolyvan’–Tomsk folded zone (KTFZ) is a late Permian collisional orogen in the northwestern section of the Central Asian Orogenic Belt. The Mesozoic history of the KTFZ area includes Late Triassic–Early Jurassic and Late Jurassic–Early Cretaceous orogenic events. The earlier event produced narrow deep half-ramp basins filled with Early–Middle Jurassic molasse south of the KTFZ, and the later activity rejuvenated the Tomsk thrust fault, whereby the KTFZ Paleozoic rocks were thrust over the Early–Middle Jurassic basin sediments. The Mesozoic orogenic events induced erosion and the ensuing exposure of granitoids (Barlak complex) that were emplaced in a within-plate context after the Permian collisional orogeny. Both events were most likely associated with ocean closure, i.e., the Paleothetys Ocean in the Late Triassic–Early Jurassic and the Mongol–Okhotsk Ocean in the Late Jurassic–Early Cretaceous. The apatite fission track (AFT) ages of granitoids from the Ob’ complex in the KTFZ range between ~120 and 100 Ma (the Aptian and the Albian). The rocks with Early Cretaceous AFT ages were exhumed as a result of denudation and peneplanation of the Early Cretaceous orogeny, which produced a vast Late Cretaceous–Paleogene planation surface. The tectonic pattern of the two orogenic events, although being different in details, generally inherited the late Paleozoic primary collisional structure of the Kolyvan’–Tomsk zone.

The article presents new data on ages (U-Pb zircon dating, SIMS SHRIMP-II) and chemical compositions of rocks from gabbro-granitic and granite-leucogranitic magmatic associations. These rocks preceded the formation of Li-enriched spodumene pegmatites of the Tserigiyngol-Burchin ore cluster (Russian: ЦБРУ), one of the main clusters in the South Sangilen pegmatite belt (SSB) located in the Tuva-Mongolian massif being a part of the Central Asian Fold Belt. We investigated the rocks from the Upper Tserigiyngol, Uchuglyk and Temenchulu plutons, and pegmatites from two neighbouring fields. We distinguish three impulses of granitic magmatism (517±7, 508±7, and 488±6 Ma), which are attributed to different stages of the Early Paleozoic collision orogeny (520-480 Ma). The period when the Li-enriched pegmatites were formed (494±7 Ma) is close to the magmatism impulse at 488±6 Ma. Differences are discovered in compositional and isotopic (Sm-Nd) features of granites dominating at the following stages of collisional orogeny: (1) early collision (517±7 Ma) – I-type granites, eNd(T)=0–1.5, TNd (DM-2st)=1.2–1.1 b.y., and (2) late collision (488±6 Ma) – A-2-type granites, eNd(T)=–3.0…–1.6, TNd (DM-2st)=1.5–1.4 b.y., which are due to different sources. Our study shows that facies transitions are absent between the late-collision granites (488±6 Ma) and the spodumene pegmatites from the Tserigiyngol-Burchin ore cluster (494±7 Ma), although these rocks are close in age. In terms of geochemical features, the spodumene pegmatites from the cluster are strongly different from both the late-collision granites and spodumene pegmatites from other SSB fields, including the large Tastyg lithium deposit. We have analysed the role of interactions between the crustal and mantle materials in the formation of granitoid sources in the Tserigiyngol-Burchin ore cluster, and described their evolution in time and the influence on the pegmatite rare-element specialization.

In the western Kunlun Mountain region, due to the convergence of the Paleotethys Ocean in the Late Paleozoic, through northward subduction towards the West Kunlun Block, forming the Kangxiwa–Waqia arc magmatism and back-arc extensional basins, including the Tamu–Kalangu and Oytag–Kurliang basins. This study explores the relationship between basin evolution and mineralization. First, the Late Paleozoic back-arc and far-field continental back-arc basins were distinguished by analyzing sediment constructions in the basins. The former was continuously deposited in the Middle Devonian–Late Permian above the Precambrian basement due to the existence of the depressions. The latter were intermittently deposited in the Middle Devonian–Late Permian due to rifting above the Caledonian orogenic belt. Although the two settings were separated by the Tiekelike fault, their formations were subject to mantle upwelling caused by the subduction of the Kangxiwa oceanic crust. We also divided the Hercynian and Indosinian magmatic activities related to the basin; the former of which included the formation of bimodal magmatic rocks (339–291 Ma) as the basin expanded, which resulted in hydrothermal sediments and hydrothermal–magmatic mineralization, mainly including volcanic massive copper sulfide, Cu and Ni sulfide, and hydrothermal deposits. During the Indosinian orogeny, intermediate acidic magmatic rocks (265–206 Ma) associated with the closure of the basin was formed, leading to the development of hydrothermal Cu–polymetallic and porphyritic copper deposits. The relationship between basin evolution and mineralization was determined. Based on the findings, we concluded that the basin extended between the Middle Devonian and Early Permian. Syngenetic sedimentary deposits formed in the closed basins and anoxic environments of local depressions and mainly included sedimentary rock-hosted stratiform Cu deposits, exhalation-sedimentary Pb–Zn deposits, and sedimentary Mn deposits. Between the Middle Permian and Early Triassic, the basin began to close and the transformation from a basin to a mountain range finally occurred. The sedimentary basement was transformed by folding and faulting, thus forming tectonic deposits, including hydrothermal vein-type Pb–Zn deposits and Cu–Pb deposits within tectonically altered rocks. The results of this work show that the Late Paleozoic extensional tectonic environment formed both the back-arc basin and the far-field continental basin simultaneously. Periods of magmatism related to rifting and convergence could be distinguished by the corresponding mineralization. The metallogenic types related to the basin could also be divided into sedimentary, magmatic hydrothermal and tectonic hydrothermal deposits.

Mafic-ultramafic subvolcanic intrusive complexes, at the 1–10-km scale, constitute favorable environments for the formation of orthomagmatic Ni-Cu-PGE sulfide deposits. Within 100–1000-km scale large igneous provinces (LIPs), the most favorable economic target areas may be difficult to identify using a traditional regional exploration approach. We report results of field and laboratory studies focused on an integrated geochemical-architectural model for the Ni-Cu-PGE sulfide potential of the High Arctic large igneous province (HALIP) of Canada, the largest and best-exposed portion of this circum-arctic LIP. Previous lithogeochemical studies of the Canadian HALIP (130–80 Ma) concluded that subalkaline mafic units located on Axel Heiberg Island were more prospective than younger, alkalic igneous rocks (alkaline basalts to basanites) exposed on northern Ellesmere Island. Mapping carried out for this study revealed the presence of abundant subalkaline igneous rocks on western Ellesmere Island. We interpret these units as an extension of the Schei Sills, a stratigraphically bound sequence of intrusions exposed along a ~ N-S belt on eastern Axel Heiberg Island. Samples from the Schei Sills and from the Middle Fiord Intrusive Complex (~ 20 km2, central Axel Heiberg Island) show Cu/Zr values above and below unity, consistent with complementary sulfide enrichment and removal, respectively, within these intrusive systems. The spatial association of the Schei Sills with the post-emplacement Eocene Stolz Thrust is noteworthy, as later thrusting associated with the Paleogene Eurekan Orogeny caused the uplift of deeper parts of the HALIP subvolcanic feeder system and associated wall-rock stratigraphy. Absolute Ir-group PGE contents are low throughout the HALIP; however, Pt-group PGE contents range widely among analyzed tholeiitic intrusive rocks. For example, relatively elevated Pt + Pd values of 10–30 ppb in samples from the Middle Fiord Intrusive Complex and the Schei Sills suggest heightened prospectivity in these two areas. In contrast, tholeiitic flood basalts in the Strand Fiord Formation and associated intrusions exposed in western Axel Heiberg Island (~ 95 Ma) exhibit Cu/Zr

The Tethys Himalaya tectonic belt has long been a passive continental margin north of Gondwana, commonly known as the Tethys Himalaya, which Indo-Asian collision orogeny developed until the Cenozoic era. It is of great scientific significance to determine its geo-tectonic evolution over geological history. Therefore, to reveal the geodynamic background of the Late Cretaceous Tethys Himalaya and its internal connection with the subduction of the Neo-Tethys ocean, in this study, we analysed the petrology, and whole-rock geochemistryof the Zongzhuo Formation basalt, which is widely distributed in the Tethys Himalaya Rongbu area. Further, we investigated the basalt types, magma source, tectonic setting and causes that gave rise to the Zongzhuo Formation to further research on the evolution of the Tethys Himalaya tectonic domain. The Zongzhuo Formation features a basalt set of compatible elements and is characterised by low Cr (average: 86.838 ppm) and enrichment of high-field-strength elements (e.g. Nb, Ta and Hf). The characteristics of the major elements, i.e. high TFeO (average: 10.43 wt %), TiO2 (average: 3.44 wt %) and P2O5 (average: 0.47 wt %), indicate an oceanic–island–basalt (OIB) geochemical signature with obvious light REE and heavy REE fractionation. The characteristics of the trace elements confirm the alkalinity of the Zongzhuo Formation basalts. Based on these results, the Zongzhuo Formation basalt was assigned to within–plate OIB. The magma might be the metasomatism products of the oceanic lithosphere mantle with low crystal fractionation and no crustal contamination, its tectonic background includes a passive–to–active transformation in the continental margin. By analysing the Tethys Himalaya belt in the south of Tibet, we concluded that the Zongzhuo Formation basalt strata in the Rongbu area were likely formed owing to Mesozoic volcanic activity and the extension and thinning of the Tethys Himalaya in the area.

The lithological-facies zoning of the Neo- and Eopleistocene sediments of the Caribbean Sea has been described for the first time based on deep-sea drilling data. Сorresponding maps and isopach schemes were processed using A.B. Ronov’s volumetric method to calculate the quantitative parameters of sedimentation for the distinguished types of Pleistocene sediments. It was revealed that the role of carbonate sediments increased from the east westward. The accumulation of lithogenic and carbonate planktic sediments was more intense in the Neopleistocene than in the Eopleistocene, which was related to the neotectonic orogeny on the Lesser Antilles.

The Salair fold-nappe terrane (a.k.a. Salair orogen, Salair) is the northwestern part of the Altai-Sayan folded area of the Central Asian Orogenic Belt. It is composed of Cambrian – Early Ordovician volcanic rocks and island-arc sedimentary deposits. In plan, Salair is a horseshoe-shaped structure with the northeast-facing convex side, which is formed by the outcrops of the Early Paleozoic folded basement. Its inner part is the Khmelev basin composed of Upper Devonian – Lower Carboniferous sandstones and siltstones. The Early Paleozoic volcanic rocks and sediments of Salair are overthrusted onto the Devonian-Permian sediments of the Kuznetsk basin. The Paleozoic thrusts, that were reactivated at the neotectonic stage, are observed in the modern relief as tectonic steps. Our study of the Salair deep structure was based on the data from two profiles of magnetotelluric sounding. These 175-km and 125-km long profiles go across the strike of the Salair structure and the western part of the Kuznetsk basin. Profile 1 detects a subhorizontal zone of increased conductivity (100–500 Ohm·m) at the depths of 8–15 km. At the eastern part of Profile 1, this zone gently continues upward, towards a shallow conducting zone that corresponds to the sediments of the Kuznetsk basin. Two high-resistance bodies (1000–7000 Ohm⋅m) are detected at the depths of 0–6 km in the middle of the section. They are separated by a subvertical conducting zone corresponding to the Kinterep thrust. The main features are the subhorizontal positions and the flattened forms of crustal conductivity anomalies. At the central part of Profile 2, there is a high-resistance block (above 150000 Ohm⋅m) over the entire depth range of the section, from the surface to the depths of about 20 km. In the eastern part of Profile 2, a shallow zone of increased conductivity corresponds to the sediments of the Kuznetsk basin. The subhorizontal mid-crust layer of increased conductivity, which is detected in the Salair crust, is typical of intracontinental orogens. The distribution pattern of electrical conductivity anomalies confirms the Salair thrust onto the Kuznetsk basin. The northern part of the Khmelev basin is characterized by high resistivity, which can be explained by abundant covered Late Permian granite massifs in that part of the Khmelev basin. The Kinterep thrust located in the northeastern part of the Khmelev basin is manifested in the deep geoelectric crust structure as a conducting zone, which can be considered as an evidence of the activity of this fault.

Tourmaline is a common mineral in granites and metamorphic rocks in collisional orogens. This paper describes graphite-bearing, metasomatic tourmalinites in sillimanite-zone schists of the Proterozoic Black Hills Orogen, South Dakota. The tourmalinites bound quartz veins and beyond about 1 m grade into schists with disseminated tourmaline, and ultimately tourmaline becomes only a trace, intrinsic phase in the schists. Next to the quartz veins, tourmaline has almost completely replaced schist minerals, including biotite, muscovite, and plagioclase. The tourmaline is generally anhedral and follows the original foliation direction of the schist. However, tourmaline is euhedral in quartz veinlets cutting through the tourmalinites. Tourmaline is compositionally zoned from having about 22 to 2% of apparent Al occupancy on the Y sites. There are very good negative correlations of Y(Fe2++Mg2+), XCa2+, and YTi4+ with YAl3+, and a very good positive correlation of X-site vacancies with YAl3+. Mg# [molar Mg2+/(Mg2++Fe2+)] is fairly invariant at approximately 0.5, which is somewhat higher than that in the precursor biotite. This is in contrast to tourmaline in the neighboring peraluminous Harney Peak leucogranite where the range of Y site occupancy of Al is small at about 20%, but the Mg# ranges from 0.12 to 0.5. The compositional trends in the metasomatic tourmaline are dominated by the exchange X☐ + 4 YAl3+ = XCa2+ + 3 Y(Fe2++Mg2+) + YTi4+. Mass-balance calculations suggest the metasomatizing fluid brought in H+ and B(OH)3 and removed K+, SiO2, and some Fe2+ during tourmalinization. Other elements in the tourmaline largely reflect the bulk composition of the replaced schist. The calculations show that silica in the quartz veins was locally derived, not brought in by the metasomatizing fluid. Interstitial graphite in the tourmalinites shows precipitation of carbon from the methane-bearing fluid. The study demonstrates an important effect of boron transfer by fluids during metamorphism and magmatism in the Earth's crust.

We analyzed new geological and geochronological data on sedimentation and metamorphism in the junction area of the Aldan and Stanovoy Superterranes comprising the southern flank of the Siberian craton. The analysis was focused on early Proterozoic deposits belonging to the Udokan group. It is confirmed that highly metamorphosed rocks at the base of the Udokan group (Kolar subgroup of the Stanovoy suture zone) differ sharply from other rock associations included in this group (Chiney and Kemen subgroups of the Aldan Superterrane). They differ in the degree of metamorphic alterations, style of tectonic deformation, igneous complexes intruding them, and show a complete lack of copper mineralization. There are thus grounds to exclude the Kolar subgroup from the Udokan group. According to our data, the age of the sediments in the Udokan group, including the Chiney and Kemen subgroups, is 1.90‒1.87 Ga, i.e. in the study area, sedimentation lasted for no more than 30 Ma and proceeded simultaneously with the copper mineralization within the intracontinental extensional basin at the stage of collapse of the early Proterozoic orogen.

Research subject. This article is devoted to the formation features of the Ural-Timan-Paleo-Asian segment of Eurasia. Materials and methods. The research was based on the authors’ data and those obtained following a review of available publications on the geology of segmentation. The Timan region was investigated using the geological information obtained by V.G. Olovyanishnikov.Results. A geodynamic map of the Ural-Timan-Paleo-Asian segment with a scale of 1 : 2 500 000 was compiled, which allowed further research into the structure and formation of the north-western part of the Eurasian area. This part was found to be mostly composed of geodynamic associations of orogens, orogenic systems and orogenic belts of the Upper Proterozoic (Riphean) and Paleozoic time intervals, as well as by elements of the Mesozoic-Cenozoic neoplate. These processes were supplemented by the formation of tectonic systems of superimposed depressions and protoplate protrusions. The formation of orogens, orogenic systems and orogenic belts is associated with the development and subsequent transformation of paleooceanic basins under the conditions of accretion and collision. The terranes of the ancient continental crust also participated in the formation of the segment’s geodynamic elements, for which a typification scheme was proposed. The articles present new data on the formation conditions of the segment’s orogenic elements and the relationship of the orogeny with global reconstructions, including the problem of closing the surrounding oceanic space.

Mountain building (orogeny) has a strong causal relationship with compression induced by plate drifting. It is generally accepted that orogenic belts are distributed perpendicular to the direction of plate movement. Extensive Late Mesozoic intra-continental deformations occurred around the North China Craton (NCC) in three different directions (i.e. EW-, WNW- and NNE-striking), which were previously attributed to three different geodynamic processes; the closure of the Mongolia-Okhotsk Ocean, convergence of the NCC and the South China block, and subduction of the paleo-Pacific plate. Remarkably, all these tectonic events were synchronised. Analogue modelling experiments were used to constrain far-field stress and basement shapes, to reconsider tectonic evolution around the NCC during this period. Results showed that all of these tectonic deformations could be plausibly interpreted as a unitary geodynamic regime governed by the westward indentation of the wedge-shaped NCC, driven by subduction of the paleo-Pacific plate. Mountain chains were formed along the edges of the wedge, indicating that the distribution of orogenic belts is not necessarily correlated with the direction of plate movement.

The Zagros Belt has examples of strike-slip faults affected by precursor Hormuz Salt bodies. We attempted to examine the role of salt walls in localizing the strike-slip faults using field observations, seismic profiles and understandings from the sandbox modeling. Setting and performance of the pre-Hormuz features in connection to the salt tectonics are major questions. The inherited topography below the salt is an important parameter which controlled the structuration of the basin. The antecedent troughs provided accommodation for the thick Hormuz Salt. Differential loading above the salt helped generation of salt-related structures. The salt-walls caused formation of elongated highs. These highs were re-shaped in form of strike-slip faults during the Zagros Orogeny. The intersection of the salt walls and the Zagros-induced deformation fronts are location of potential diapirs needless of bending points along the tear faults. In contrast, the underlying deep-seated basement faults are hardly believed to be strike-slip.

The small Kedengjian volcanic rock-hosted hydrothermal vein-type Cu deposit (100,000 t Cu metal content at about 3% Cu) is located in the Lanping Basin, one of several Mesozoic–Cenozoic continental sedimentary basins in the northern part of the Indochina block and in the eastern part of the North Qiangtang block. Many sediment-hosted base metal ore deposits with ages of

The structure of the lithosphere-asthenosphere system as imaged from the complementary inversion of seismological and gravimetric data can provide significant clues to understand the processes of orogeny and cratonization and to better formulate the theory of plate tectonics within a sound geodynamic context. In this paper, we review some studies sharing a common synergic methodology that uses the geometry of cellular shear-waves velocity models of the crust and uppermost mantle to constrain a 3D density model obtained by means of linear inversion of gravimetric data. These studies, which were applied to selected areas along an ideal stream running from the Periadriatic region to the Himalayas, despite having different resolution, show some basic common features in the density distribution of the upper mantle whose unveiling may be precluded to gravity models achieved by assuming velocity-density relationships. In fact, one of the main conclusions of the discussed studies is that lithospheric slabs under the investigated orogenic belts, as identified by seismic waves velocity, are, as a rule, not marked by high density. This fact casts serious doubts about the effectiveness of slab-pull and confirms one of the key issues of polarized plate tectonics, mostly fuelled by tidal drag.

Multiple tectonic movements and charge episodes have occurred in the Tazhong Uplift of the Tarim Basin, NW China, contributing to widespread solid bitumen, heavy oil, normal oil, condensate and gas in the Shuntuoguole High, especially in the Lower Silurian Kepingtage Formation. A detailed investigation of cores and fluid inclusions from different intervals, i.e. S1k3−3, S1k3−1, S1k1, has been carried out using petrographic analysis, gas chromatograph–mass spectrometry and micro–Fourier transform infrared spectroscopy. Three hydrocarbon charge events in the Kepingtage Formation have been recognized associated with the late Caledonian, late Hercynian and Himalayan orogenies. In the late Caledonian, oils were charged into the S1k3−3, S1k3−1 and S1k1 intervals, but evolved to solid bitumen due to biodegradation and water washing, as the Silurian strata have experienced both strong uplift and erosion during the early Hercynian Orogeny, and the influence of igneous intrusions during the Permian. Hydrocarbons associated with the Caledonian contain no regular steranes, diasteranes, hopanes or extended tricyclic terpanes due to in-reservoir thermal cracking. The second charge period occurred in the late Hercynian, which has experienced severe biodegradation and water washing. Hydrocarbons of this period are characterized by an obvious chromatographic hump of the unresolved complex mixture (UCM) coupled with petroleum inclusions that fluoresce light-blue and yellow, possibly indicating variable maturity. Whether or not high maturity oil charged during this period into the S1k1 interval has commercial production value needs further investigation. The third change occurred during the Himalayan Orogeny. Highly mature hydrocarbons were emplaced into the S1k3−3, S1k3−1 and S1k1 intervals with the S1k1 interval as being the most significant. Biodegradation, water washing, and igneous intrusion had no impact on hydrocarbons charged during this period, resulting in higher potential for economic production.

The Collisional Orogeny in the Scandinavian Caledonides (COSC) scientific drilling project aims to characterise the structure and orogenic processes involved in a major collisional mountain belt by multidisciplinary geoscientific research. Located in western central Sweden, the project has drilled two fully cored deep boreholes into the bedrock of the deeply eroded Early Paleozoic Caledonide Orogen. COSC-1 (2014) drilled a subduction-related allochthon and the associated thrust zone. COSC-2 (2020, this paper) extends this section deeper through the underlying nappes (Lower Allochthon), the main Caledonian décollement, and the upper kilometre of basement rocks. COSC-2 targets include the characterisation of orogen-scale detachments, the impact of orogenesis on the basement below the detachment, and the Early Paleozoic palaeoenvironment on the outer margin of palaeocontinent Baltica. This is complemented by research on heat flow, groundwater flow, and the characterisation of the microbial community in the present hard rock environment of the relict mountain belt. COSC-2 successfully, and within budget, recovered a continuous drill core to 2276 m depth. The retrieved geological section is partially different from the expected geological section with respect to the depth to the main décollement and the expected rock types. Although the intensity of synsedimentary deformation in the rocks in the upper part of the drill core might impede the analysis of the Early Paleozoic palaeoenvironment, the superb quality of the drill core and the borehole will facilitate research on the remaining targets and beyond. Protocols for sampling in the hard rock environment and subsequent sample preservation were established for geomicrobiological research and rock mechanical testing. For the former, a sparse sample series along the entire drill core was taken, while the target of the latter was the décollement. COSC-2 was surveyed by a comprehensive post-drilling downhole logging campaign and a combined borehole/land seismic survey in autumn 2021. This paper provides an overview of the COSC-2 (International Continental Scientific Drilling Project – ICDP 5054_2_A and 5054_2_B boreholes) operations and preliminary results. It will be complemented by a detailed operational report and data publication. Collisional Orogeny in the Scandinavian Caledonides (COSC)

Graphite forms the endpoint for organic carbon metamorphism; it is extremely resilient to physical, biological and chemical degradation. Carbonaceous materials (CM) contained within sediments, collected across Taiwan and from the Gaoping submarine canyon, were analyzed using Raman spectroscopy to determine the crystallinity. This allowed the erosional and orogenic movements of petrogenic organic carbon (OCpetro) during the Taiwanese orogeny to be deduced. After automatically fitting and classifying spectra, the distribution of four groups of CM within the sediments provides evidence that many forms of OCpetro have survived at least one previous cycle of erosion, transport and burial before forming rocks in the Western Foothills of the island. There is extensive detrital graphite present in rocks that have not experienced high-grade metamorphism, and graphite flakes are also found in recently deposited marine sediments off Taiwan. The tectonic and geological history of the island shows that these graphite flakes must have survived at least three episodes of recycling. Therefore, transformation to graphite during burial and orogeny is a mechanism for stabilizing organic carbon over geological time, removing biospheric carbon from the active carbon cycle and protecting it from oxidation during future erosion events., Zweitver��ffentlichungen der Universit��t Potsdam : Mathematisch-Naturwissenschaftliche Reihe; 1223

The northern North Sea rift evolved through multiple rift phases within a highly heterogeneous crystalline basement. The geometry and evolution of syn‐rift depocenters during this multiphase evolution and the mechanisms and extent to which they were influenced by preexisting structural heterogeneities remain elusive, particularly at the regional scale. Using an extensive database of borehole‐constrained 2D seismic reflection data, we examine how the physiography of the northern North Sea rift evolved throughout late Permian‐Early Triassic (RP1) and Late Jurassic‐Early Cretaceous (RP2) rift phases, and assess the influence of basement structures related to the Caledonian orogeny and subsequent Devonian extension. During RP1, the location of major depocenters, the Stord and East Shetland basins, was controlled by favorably oriented Devonian shear zones. RP2 shows a diminished influence from structural heterogeneities, activity localizes along the Viking‐Sogn graben system and the East Shetland Basin, with negligible activity in the Stord Basin and Horda Platform. The Utsira High and the Devonian Lomre Shear Zone form the eastern barrier to rift activity during RP2. Toward the end of RP2, rift activity migrated northward as extension related to opening of the proto‐North Atlantic becomes the dominant regional stress as rift activity in the northern North Sea decreases. Through documenting the evolving syn‐rift depocenters of the northern North Sea rift, we show how structural heterogeneities and prior rift phases influence regional rift physiography and kinematics, controlling the segmentation of depocenters, as well as the locations, styles, and magnitude of fault activity and reactivation during subsequent events. publishedVersion

The spatial-temporal extent and influence of the Mongol-Okhotsk and Paleo-Pacific tectonic regimes in northeast (NE) China and adjacent areas during late Mesozoic times have long been controversial. As a superimposed rift system which formed due to extensive intracontinental extension during the Late Jurassic to Early Cretaceous periods, the Hailar-Tamtsag basin is a key area to study the relationship between the Mongol-Okhotsk and Paleo-Pacific tectonic regimes and their superposition. With the aim of constraining the evolution of those two regimes, in this paper, the Tanan depression, which is a second-order structural unit in the western part of the Hailar-Tamtsag basin, has been chosen as the research object. On the basis of structural analysis of three-dimensional (3D) seismic data in the Tanan depression, and taking into account the controlling effect and influence of the pre-existing facies on the basin evolution, the deformation events in the Early Cretaceous can be subdivided into four periods: 1) A NW-SE trending extension during the deposition of the Tongbomiao Formation to the upper part of the second Member of the Nantun Formation; 2) A NW-SE trending compression during the deposition of the upper part of the second Member of the Nantun Formation to the first Member of the Yimin Formation; 3) A near EW trending extension during the deposition of the second Member to the lower part of third Member of the Yimin Formation; 4) A near EW trending compression during the deposition of the upper part of the third Member of the Yimin Formation. Additionally, we identify compressional structures in the basement in the southeast part of the depression, which is a key study that resulted from the Mongol-Okhotsk collisional orogeny during the Late Jurassic. The above five major deformational events make up a relatively complete tectonic deformation sequence of the Hailar-Tamtsag basin. Moreover, the deformation sequence, together with other available information from the literature in NE China and adjacent areas, including petrology, geochemistry and geochronology data, also record the whole process from the orogenic stage after the closure of the Mongol-Okhotsk Ocean, over the post-orogenic collapse of the Mongol-Okhotsk orogen, to the weakening of the influence of the Mongol–Okhotsk regime, and eventually to be replaced by the Paleo-Pacific tectonic regime. Considering that the superposition and transformation of the two tectonic regimes involves almost all the geological process in NE China and adjacent area during the late Mesozoic, the complete geological record in the Tanan depression during this period provides new constraints on the research of regional tectonic evolution, and the model of multiphase deformation is also expected to have useful implications for future studies of complex basin systems.

The nature of the lower crust and the crust-mantle transition is fundamental to Earth sciences. Transformation of lower crustal rocks into eclogite facies is usually expected to result in lower crustal delamination. Here we provide compelling evidence for long-lasting presence of lower crustal eclogite below the seismic Moho. Our new wide-angle seismic data from the Paleoproterozoic Fennoscandian Shield identify a 6–8 km thick body with extremely high velocity (Vp ~ 8.5–8.6 km/s) and high density (>3.4 g/cm3) immediately beneath equally thinned high-velocity (Vp ~ 7.3–7.4 km/s) lowermost crust, which extends over >350 km distance. We relate this observed structure to partial (50–70%) transformation of part of the mafic lowermost crustal layer into eclogite facies during Paleoproterozoic orogeny without later delamination. Our findings challenge conventional models for the role of lower crustal eclogitization and delamination in lithosphere evolution and for the long-term stability of cratonic crust., The nature of the lower crust and the crust-mantle transition is fundamental to Earth Sciences. Here, the authors provide evidence for long-lasting presence of lower crustal eclogite below the seismic Moho, challenging conventional models.

The present study investigates the reasons for the heavy siltation in Chilka Lake which is analysed by satellite imagery, ground survey and geophysical studies. Modified normalized difference water index (MNDWI) and linear spectral unmixing method (LSU) reveal the presence of a wetland, suspended sediments and aquatic weeds along the northeastern boundary of the lake and beyond. Gravity, magnetic data and 3D inversion modelling reveal various sets of faults that were periodically reactivated to form uplifted and subsided blocks around the lake. Geomorphic evidence like low valley width/height ratio (Vf) with

The cross-correlation of ambient noise records registered by seismic networks has proven to be a valuable tool to obtain new insights into the crustal structure at different scales. Based on 2 to 14 s period Rayleigh and Love dispersion data extracted from the seismic ambient noise recorded by 20 three-component broadband stations belonging to two different temporary experiments, we present the first (i) upper-crustal (1–12 km) high-resolution shear wave velocity and (ii) radial anisotropy variation models of the continental crust in NW Iberia. The area of study represents one of the best-exposed cross sections along the Variscan orogen of western Europe, showing the transition between the external eastern zones towards the internal areas in the west. Both the 2-D maps and an E–W transect reveal a close correspondence with the main geological domains of the Variscan orogen. The foreland fold-and-thrust belt of the orogen, the Cantabrian Zone, is revealed by a zone of relatively low shear wave velocities (2.3–3.0 km s−1), while the internal zones generally display higher homogeneous velocities (> 3.1 km s−1). The boundary between the two zones is clearly delineated in the models, depicting the arcuate shape of the orogenic belt. The velocity patterns also reveal variations of the elastic properties of the upper crust that can be linked to major Variscan structures, such as the basal detachment of the Cantabrian Zone, the stack of nappes involving pre-Variscan basement, or sedimentary features such as the presence of thick syn-orogenic siliciclastic wedges. Overall, the radial anisotropy magnitude varies between −5 % and 15 % and increases with depth. The depth pattern suggests that the alignment of cracks is the main source of anisotropy at < 8 km depths, although the intrinsic anisotropy seems to be significant in the West Asturian–Leonese Zone, the low-grade slate belt adjacent to the Cantabrian Zone. At depths > 8 km, widespread high and positive radial anisotropies are observed, which we attribute to the presence of subhorizontal alignments of grains and minerals in relation to the pre- or syn-orogenic deformation associated with the Variscan orogenesis.

The eastern margin of North America has been shaped by a series of tectonic events including the Paleozoic Appalachian Orogeny and the breakup of Pangea during the Mesozoic. For the past similar to 200 Ma, eastern North America has been a passive continental margin; however, there is evidence in the Central Appalachian Mountains for post-rifting modification of lithospheric structure. This evidence includes two co-located pulses of magmatism that post-date the rifting event (at 152 and 47 Ma) along with low seismic velocities, high seismic attenuation, and high electrical conductivity in the upper mantle. Here, we synthesize and evaluate constraints on the lithospheric evolution of the Central Appalachian Mountains. These include tomographic imaging of seismic velocities, seismic and electrical conductivity imaging along the Mid-Atlantic Geophysical Integrative Collaboration array, gravity and heat flow measurements, geochemical and petrological examination of Jurassic and Eocene magmatic rocks, and estimates of erosion rates from geomorphological data. We discuss and evaluate a set of possible mechanisms for lithospheric loss and intraplate volcanism beneath the region. Taken together, recent observations provide compelling evidence for lithospheric loss beneath the Central Appalachians; while they cannot uniquely identify the processes associated with this loss, they narrow the range of plausible models, with important implications for our understanding of intraplate volcanism and the evolution of continental lithosphere. Our preferred models invoke a combination of (perhaps episodic) lithospheric loss via Rayleigh-Taylor instabilities and subsequent small-scale mantle flow in combination with shear-driven upwelling that maintains the region of thin lithosphere and causes partial melting in the asthenosphere. U.S. National Science Foundation EarthScope programNational Science Foundation (NSF)NSF - Directorate for Geosciences (GEO) [EAR-1460257, EAR-1249412, EAR-1249438, EAR-1250988, EAR-1251538, EAR-1251515]; United States National Science FoundationNational Science Foundation (NSF) [EAR-1261681]; U.S. National Science Foundation GeoPRISMS program [EAR-1460257, EAR-1249412, EAR-1249438, EAR-1250988, EAR-1251538, EAR-1251515] Published version This work benefited from discussions at the EarthScope Synthesis Workshop on the Evolution of the Southern Appalachian Lithosphere, held at Brown University in March 2017. The authors acknowledge support from the U.S. National Science Foundation EarthScope and GeoPRISMS programs via grants EAR-1460257 (R. L. Evans), EAR-1249412 (E. Gazel), EAR-1249438 (E. A. Johnson), EAR-1250988 (S. D. King), EAR-1251538 (E. Kirby), and EAR-1251515 (M. D. Long). The authors thank Randy Keller for making the PACES gravity data available. The collection and dissemination of most of the geophysical data and models discussed in this study were facilitated by the Incorporated Research Institutions for Seismology (IRIS). The facilities of the IRIS Consortium are supported by the United States National Science Foundation under Cooperative Agreement EAR-1261681. The authors thank two anonymous reviewers whose valuable comments have helped us to improve the quality of the article. For the past 200 million years, the east coast of North America has been situated in the middle of a tectonic plate. Contrary to the expectations for this setting, a region of the Central Appalachian Mountains centered near the boundary between the U.S. states of Virginia and West Virginia exhibits atypical properties. The unusual observations include volcanic activity in the geologic past far away from a plate boundary, elevated rates of erosion associated with high topography in the Central Appalachians, and anomalous structure in the upper mantle that has been detected using geophysical methods. This article describes, synthesizes, and compares a suite of observations that show that this part of the Central Appalachians is unusual compared to other so-called passive continental margins. We discuss a range of different models that might describe how the lithosphere, or the rigid part of the crust and upper mantle that defines the tectonic plate, has evolved through time beneath our study region. We show that the lithosphere today is thin, and that past episodes of lithospheric loss involving a portion of dense lithosphere "dripping" into the mantle under the force of gravity may provide a good explanation for the observations.

International audience; Exhumation of the roots of collapsing orogens is a key process in the evolution of mountain belts, which is critical for the understanding of orogenic cycles. From new structural analyses, K-Ar and 40 Ar/ 39 Ar on muscovite, biotite and K-feldspar, and available U-Pb ages, we constrain the cooling and exhumation history of granitic batholiths from the main structural zones of the Variscan orogen in Iberia. We show that: (1) the oldest Ar dated granites (ca. 335 Ma on biotite) record exhumation of gneisses crystallized much earlier (up to ca. 530-510 Ma U-Pb age); (2) granitoids crystallized at ca. 330 Ma record mostly ductile stretching (L-tectonites striking around N-S), consistent with N-S extension (Variscan intra-orogenic collapse); (3) most granites crystallized between ca. 320 and 305 Ma record ductile stretching consistent with deformation along NW-SE to ENE-WSW shear zones during the late-Variscan compression (C3); (4) granites crystallized after 305 Ma record mostly isotropic strain (no visible ductile foliation or lineation), consistent with their emplacement during/after the final collapse of the Variscan orogeny (E2); (5) comparison between Ar ages on micas and zircon U-Pb ages shows two contrasting situations: (i) similar ages, reflecting crystallization and fast cooling, which can be explained by relatively shallow intrusion and/or fast tectonic uplift; (ii) significant difference between U-Pb and Ar ages, supporting crystallization of deeper seated intrusions and their subsequent uplift for several Ma to tens of Ma; (6) thermochronological modelling on K-feldspar supports significant tectonic exhumation in the core of the chain between ca. 315 and 285 Ma, followed by late-stage passive denudation; 7) Late Carboniferous to early Permian tectonic exhumation was accompanied by significant formation of ore-deposits. Tin deposits occur in pegmatites and/or quartz veins associated with muscovite-rich syn-C3 granites and those of tungsten in quartz veins, breccia pipes and skarns associated with the E2 biotite-rich granites.

Author(s): Park, Y; Swanson-Hysell, NL; Xian, H; Zhang, S; Condon, DJ; Fu, H; Macdonald, FA | Abstract: The Tonian supercontinent Rodinia is hypothesized to have included almost all Proterozoic continental blocks. Competing models variably place South China at the core or periphery of Rodinia or separated from it entirely. Tonian paleogeographic models also vary in whether they incorporate hypothesized large and rapid oscillatory true polar wander associated with the ca. 810–795nMa Bitter Springs Stage. Here, we present paleomagnetic data paired with U-Pb chemical abrasion isotope dilution thermal ionization mass spectrometry zircon geochronology from the Tonian Xiajiang Group in South China to establish the craton's position and test the Bitter Springs Stage true polar wander hypothesis. Fine-grained siliciclastic sediments and ashes of the Xiajiang Group post-date the Jiangnan Orogeny, which united the Yangtze and Cathaysia blocks. A U-Pb zircon date of 815.73n±n0.18nMa from a tuff near the base of the Xiajiang Group constrains the Jiangnan Orogeny to have ended between ca. 830 and 816nMa. The paleomagnetic and geochronologic data constrain South China to high latitudes ca. 813nMa and indicate a relatively stable high-latitude position from ca. 821 to 805nMa. These high-latitude constraints either connect the craton to Rodinia along its periphery or disconnect it from the supercontinent entirely. The difference in pole position between the pre-Bitter Springs Stage Xiajiang Group pole and the syn-Bitter Springs Stage Madiyi Formation pole is significantly less than that predicted for the Bitter Springs Stage true polar wander hypothesis. If this pole difference is interpreted as true polar wander superimposed upon differential plate motion, it requires South China to have been separate from Rodinia.

The ~ 1.5 Moz Yaoure gold deposit, which is located within the Birimian greenstone belts of central Cote d’Ivoire (West Africa), is associated with two stages of economic gold mineralization. Both ore-forming stages occurred during protracted E-W-directed shortening associated with the Eburnean orogeny. The first mineralization stage is hosted by fault-fill veins along conjugate ENE-striking (dextral) and WNW-striking (sinistral) strike-slip fault arrays. This ore stage is associated with a polymetallic assemblage including Mo, Bi, Pb, W, Te, Ag, and Au and cryptic alteration in wall rocks. The second and main gold mineralization stage is associated with a low-displacement fault-fracture-vein mesh formed during a reverse faulting episode. This second gold phase is associated with a polymetallic assemblage including W and Au ± Pb and is characterized by pronounced albite-ankerite-pyrite hydrothermal alteration in wall rocks. Shear veins associated with this second mineralization episode formed during episodic fluid pressure variations under low differential stress within pre-existing low-angle reverse fault planes. Permeability destruction by albite-ankerite-pyrite hydrothermal sealing of these low-angle reverse faults resulted in fluid pressure build-up and ultimately in the development of extension veins under low differential stress in the late stages of the structural evolution of the deposit. This study presents the structural evolution of a polyphase orogenic gold deposit and highlights that the interplay between fault zone activity, hydrothermal alteration, and fluid pressure fluctuations at low differential and deviatoric stresses were key in controlling fluid flow and the formation of ore within optimally-oriented faults.

Synthesis of new and existing field, structural, geochemical, isotopic, and geochronologic data in the Adirondack Highlands of the southern Grenville Province indicate a suite of arc plutonic rocks (Piseco Lake granite suite) was intruded into basement rocks from ca. 1205–1180 Ma due to northward subduction beneath the Laurentian margin. Although rocks of similar age and origin are found in the Adirondack Lowlands and elsewhere in the Highlands, they occur in the greatest volume and are most intensely deformed in the Piseco Lake Shear Zone (PLSZ). This structure separates the Adirondack Highlands from ca. 1350-1300 Ma tonalitic gneisses in the southern Adirondacks. Tectonites in the PLSZ record the deformation of a continental arc batholith during collision with an outboard terrane which was accreted to Laurentia during the Shawinigan Orogeny. Internal to the PLSZ, a 10–15 km wide, subvertical zone of subhorizontally lineated L-S and L-tectonites (Piseco Lake gneisses) was derived primarily from megacrystic arc plutonic protoliths and documents sinistral relative motion. Intrusion of the arc granitoids, deformation and anatexis (ca. 1180–1160 Ma) throughout the entire Adirondack region immediately preceded and overlapped the intrusion of the anorthosite-mangerite-charnockite-granite (AMCG) suite at ca. 1165-1145 Ma in the Adirondack Highlands. We hypothesize that delamination or slab detachment, in combination with an irregular Laurentian margin, triggered disruption of the underlying lithosphere, allowed ascent of enriched asthenosphere, and facilitated the intrusion of voluminous AMCG rocks in the Adirondacks north of the PLSZ. Other large anorthosite massif complexes in the southern Grenville Province, including the Morin and Lac St. Jean bodies near the Laurentian margin, have also been linked to Shawinigan convergent structures and were an important part of accretionary processes documented in the Grenville Orogen.

The world’s largest ongoing collisional orogeny is the Europe Alps–Himalayan–SE Asian belt and is a natural laboratory to understand many processes that have shaped the continents. Due to political instability and conflict throughout this millennium, the Iraq (Kurdish) sector of the Zagros mountain chain is the least studied part of this orogenic system. In Iraq, the Zagros contains the suture between the Arabian subcontinent to the south and west and the Iranian edge of the Eurasian continent to the north and east. The suture zone is marked by several allochthons of Neotethyan ophiolitic and volcanic arc assemblages that were obducted onto the Arabian margin. New geochronological data, including SHRIMP U-Pb zircon, integrated with whole rock geochemistry, indicates that both Cretaceous (˜96 Ma) and Cenozoic (˜40 Ma) assemblages are present. The relationships between these units are complicated, thus some Cretaceous arc rocks were intruded by Cenozoic arc rocks, and out-of-sequence thrusting has interleaved and juxtaposed assemblages of different ages. Ongoing wrench faulting since continental collision at ˜14 Ma has further complicated the pattern of lithotectonic units, particularly those that were obducted out of the Neotethyan realm. The new data indicate that the Iraqi sector of Neotethys was not ‘quiet’ in the Cretaceous, but contains fragments of arcs of that age, contiguous with those along strike in Turkey, Iran and the Himalayas.

In the area of the Central Europe three large continental scale tectonic units meet together, namely Precambrian East European Craton (EEC) to the northeast, Variscan West European Platform (WEP) terranes to the southwest, and younger Alpine Carpathian arc in the south. The reference structure of the Central Europe is a sharp edge of the East European Craton. In the area of Poland the south-western margin of the EEC is marked as Teisseyre–Tornquist Zone (TTZ), which continues to the north as Sorgenfrei–Tornquist Zone (STZ). Teisseyre–Tornquist Zone (TTZ) — earlier Teisseyre Line, Tornquist Line or Teisseyre–Tornquist Line (TTL), is a term created in commemoration of Polish geologist Wawrzyniec Teisseyre and German geologist and paleontologist Alexander Tornquist. At the turn of XIX and XX century, they noticed a fundamental difference in the geology of platform cover between the rigid East European Platform and its more mobile southwestern forefield (Teisseyre, 1893, 1903; Tornquist, 1908, 1910). From the very beginning the TTL was conceived as a linear feature (fault or fault zone) marking the southwestern boundary of the EEC. Contrarily, the Trans–European Suture Zone (TESZ) is a term coined by Asger Berthelsen for an assemblage of suspect terranes boarded by the East European Craton and the Variscan orogeny. It is not a linear structure, but a terrane accretion zone, 100–200 km wide. Both terms, TTL and TESZ, should not be mistaken, as is the case on many maps concerning the problem (Dadlez et al., 2005). The edge of the craton is a major lithospheric structure, which appears to be a deep-seated boundary reaching at least down to a depth of about 200 km as shown by tomographic analysis of shear wave velocity structure of the mantle under Europe. Another indication of the deep-seated nature of this zone was obtained from observations of earthquakes and explosions located in Europe. To explain the observed blockage of energy from regional seismic events by TTZ, the structural anomaly between eastern and western Europe must reach at least down to a depth of about 200 km. Continental scale tectonic units of the Central Europe are clearly visible in the crustal structure, Moho depth map, and also gravity, magnetic and heat flow maps.

Over geological timescales, mountain building or orogenesis is associated with increased weathering, the drawdown of atmospheric CO2, and global cooling. However, a multimillion‐year delay appears to exist between peaks in low‐latitude mountain uplift and the maximum extent of Phanerozoic glaciation, implying a more complex causal relationship between the two. Here we show that global silicate weathering can be modulated by orogeny in three distinct phases. High, young mountain belts experience preferential precipitation and the highest erosion. As mountains are denuded, precipitation decreases, but runoff temperature rises, sharply increasing chemical weathering potential and CO2 drawdown. In the final phase, erosion and weathering are throttled by flatter topography. We conclude that orogeny acts as a capacitor in the climate system, granting the potential for intense transient CO2 drawdown when mountain ranges are denuded; the mechanism suggests such a scenario potentially happening 10‐50 million years in the future.

International audience; Since the discovery of shatter cones (SCs) near the village of Agoudal (Morocco, Central High Atlas Mountains) in 2013, the absence of one or several associated circular structures led to speculation about the age of the impact event, the number, and the size of the impact crater or craters. Additional constraints on the crater size, age, and erosion rates are obtained here from geological, structural, and geophysical mapping and from cosmogenic nuclide data. Our geological maps of the Agoudal impact site at the scales of 1:30,000 (6 km(2)) and 1:15,000 (2.25 km(2)) include all known occurrences of SCs in target rocks, breccias, and vertical to overturned strata. Considering that strata surrounding the impact site are subhorizontal, we argue that disturbed strata are related to the impact event. Three types of breccias have been observed. Two of them (br1-2 and br2) could be produced by erosion-sedimentation-consolidation processes, with no evidence for impact breccias, while breccia (br1) might be impact related. The most probable center of the structure is estimated at 31 degrees 59 ' 13.73"N, 5 degrees 30 ' 55.14"W using the concentric deviation method applied to the orientation of strata over the disturbed area. Despite the absence of a morphological expression, the ground magnetic and electromagnetic surveys reveal anomalies spatially associated with disturbed strata and SC occurrences. The geophysical data, the structural observations, and the area of occurrence of SCs in target rocks are all consistent with an original size of 1.4-4.2 km in diameter. Cosmogenic nuclide data (Cl-36) constrain the local erosion rates between 220 +/- 22 m Ma(-1) and 430 +/- 43 m Ma(-1). These erosion rates may remove the topographic expression of such a crater and its ejecta in a time period of about 0.3-1.9 Ma. This age is older than the Agoudal iron meteorite age (105 +/- 40 kyr). This new age constraint excludes the possibility of a genetic relationship between the Agoudal iron meteorite fall and the formation of the Agoudal impact site. A chronolgy chart including the Atlas orogeny, the alternation of sedimentation and erosion periods, and the meteoritic impacts is presented based on all obtained and combined data.

Volcanism provides a reliable record of local and global tectonic events and substantially influences both modern and ancient environments, climates, and the evolution of life. The Ordovician–Silurian (O–S) transition is a special period because intensive volcanism occurred globally, including in the Yangtze region of South China. Volcanic events during this period are a symptom of plate tectonic behaviour and are thought to be responsible for the remarkable changes in climate in the early Palaeozoic, though the relationships between these events remain unclear and controversial. Coeval igneous rocks and volcanic sediments (VS) are primarily used to resolve this issue. However, limited studies have been performed on VS from the O–S transition in South China. Recently, a typical VS-bearing section was found in the Lower Yangtze region, which contains ∼100 thin, interbedded volcanic ash layers across the O–S transition. Detailed petrographic and geochemical analyses of the volcanic ashes were conducted to determine their isotopic ages, magma sources, evolutionary processes, and tectonic settings. Our preliminary results suggest that volcanic eruptions in South China lasted for more than 22 Ma across the O–S boundary, from ∼449.3 ± 3.6 to 427.6 ± 4.1 Ma, where 445.14 Ma is the lowermost graptolite biozone for Metabolograptus extraordinarius, as well as the initiation of the Late Ordovician mass extinction (LOME) event in the Yangtze region. The evolutionary history of the parental magma was constructed from a depleted mantle source in the early stage and from a crustal source in the late stage, with several transitional features in the middle. The mantle source and arc-related geochemical indicators for the volcanic ashes support the disputed “subduction-collision orogeny” model. We propose that the strong volcanism in South China, accompanied by volcanism in numerous other regions worldwide, was an important trigger for the LOME and was likely responsible for oceanic 87Sr/ 86Sr fractionation and other climatic changes during the O–S transition.

Key in understanding the geodynamics governing subduction and orogeny is reconstructing the paleogeography of ‘Greater India’, the Indian plate lithosphere that subducted since Tethyan Himalayan continental collision with Asia. Here, we discuss this reconstruction from paleogeographic, kinematic, and geodynamic perspectives and isolate the evolution scenario that is consistent with all three. We follow recent constraints advocating a ~58 Ma initial collision and update a previous kinematic restoration of intra-Asian shortening with a recently proposed model that reconciles long-debated large and small estimates of Indochina extrusion. Our new reconstruction is tested against paleomagnetic data, and against seismic tomographic constraints on paleo-subduction zone locations. The resulting restoration shows ~1000–1200 km of post-collisional intra-Asian shortening, leaving a 2600–3400 km wide Greater India. From a paleogeographic, sediment provenance perspective, Eocene sediments in the Lesser Himalaya and on undeformed India may be derived from Tibet, suggesting that all Greater Indian lithosphere was continental, but may alternatively be sourced from the contemporaneous western Indian orogen unrelated to India-Asia collision. A quantitative kinematic, paleomagnetic perspective prefers major Cretaceous extension and a ‘Greater India Basin’ opening within Greater India, but data uncertainty may speculatively allow for minimal extension. Finally, from a geodynamic perspective, assuming a fully continental Greater India would require that subduction rates close to 20 cm/yr was driven by a down-going lithosphere-crust assemblage more buoyant than the mantle, which seems physically improbable. We conclude that the Greater India Basin scenario is the only sustainable one from all three perspectives. We infer that old pre-collisional lithosphere rapidly entered the lower mantle sustaining high subduction rates, whilst post-collisional continental and young Greater India basin lithosphere did not, inciting the rapid India-Asia convergence deceleration ~8 Myr after collision. Subsequent absolute northward slab migration and overturning caused flat slab subduction, Tibetan shortening, arc migration and arc volume decrease.

The Huizachal–Peregrina Anticlinorium basement of the Sierra Madre Oriental in north-eastern (NE) Mexico comprises a wide variety of Precambrian and Paleozoic units. A granitic unit, described in this work as the Peregrina Tonalite (PTo), intruded the Neoproterozoic Novillo Gneiss, which is the northernmost expression of the Oaxaquia microcontinent. In contrast, the PTo’s contact with the Carboniferous Granjeno Schist is tectonic along vertical faults with a strike-slip component. This Paleozoic lithodeme is part of the Granjeno–Acatlan Belt. The PTo has been described as an orphaned block associated with an enigmatic Carboniferous magmatic arc located along the north-western (NW) margin of Gondwana. In this study, new U–Pb LA–ICP–MS data from PTo zircons included a youngest Late Ordovician (Katian stage) population at 448.8 ± 2.9 Ma, interpreted as the crystallisation age, and an oldest Grenvillian population interpreted as the potential age of its protolith. Additionally, major and trace element concentrations and ratios indicate a link to a continental arc that developed along the NW margin of Gondwana. Given this proposed arc’s age and position, a comprehensive model for the development of the NE Mexican basement without the involvement of exotic or orphaned terranes is now proposed. The PTo outcropping near Ciudad Victoria, Tamaulipas, is interpreted to be part of a previously unreported magmatic arc in NE Mexico established during the Late Ordovician, herein described as the Peregrina–Mochonian Orogeny. It represents an extension of the South American Famatinian arc into Mexico.

The Bonikro gold deposit and satellite Hire open pits are located at the southern tip of the Oume-Fettekro granite–greenstone belt in Cote d’Ivoire. Country rocks in the region have undergone polyphase deformation and prolonged arc magmatism during the Paleoproterozoic Eburnean orogeny. Intrusive host rocks at Hire and Bonikro have been dated at 2180 ± 6 and 2086 ± 4 Ma (U–Pb on zircon), respectively. These plutonic bodies acted as favourable sites for fluid flow due to their brittle rheological characteristics. Gold mineralisation at Bonikro is hosted by (i) a sheeted quartz vein array characterised by an Au–W–Bi–Te–Ag metal association, in the cupola of a porphyritic granodiorite; and (ii) an overprinting swarm of fault-fill smoky quartz–(molybdenite) veins. Gold mineralisation at Hire is shear-hosted and shares a similar relative timing with the latter set of auriferous veins. This second phase of gold mineralisation occurred during a period of transcurrent tectonics late in the Eburnean tectono-magmatic history, soon after the cessation of compressional deformation. It is responsible for the bulk of gold resources in the region (e.g. Bonikro, Hire, Agbahou) and has been dated at 2074 ± 16 Ma (Re–Os on molybdenite). The integration of structural–paragenetic relationships with high precision dating of magmatic and hydrothermal events highlights the superposition of late Eburnean orogenic gold mineralisation on an earlier intrusion-related gold system linked to the local emplacement of a porphyritic granodiorite at Bonikro and illustrates the genetic diversity of Paleoproterozoic granitoid-hosted gold mineralisation in the West African Craton. It also further supports that gold mineralisations in the West African Craton occurred diachronously throughout the Eburnean orogeny through a variety of deposit types including Au-skarn, intrusion-related Au, orogenic Au, and porphyry Cu–Au.

The Paleozoic tectonic history of the Tasmanides in eastern Australia was dominated by subduction-related processes along the margin of eastern Gondwana. The earliest deformation event, Delamerian Orogeny, took place in the middle-late Cambrian and is recorded in rocks within the Delamerian and Thomson orogens. The Cambrian-Ordovician Warburton Basin covers the boundary between the Delamerian and Thomson Orogens, but very little is known about its origin and deformation history. Here we interpret geophysical data, including 2-D seismic reflection transects, Bouguer gravity, and aeromagnetic data that provide new insights into the deformation in the eastern Warburton Basin and the kinematics of major faults. Our results show that curvilinear NE-trending faults in the eastern Warburton Basin are basement reverse faults that experienced multiple phases of contractional deformation. Evidence for a syn-kinematic Cambrian package (Kalladeina Formation) suggests that faulting commenced in response to the Delamerian Orogeny. A subsequent Early Devonian deformation in the eastern Warburton Basin is evident from K-Ar geochronology of low-grade (subgreenschist) metasedimentary rocks. We suggest that the NE-trending Cambrian fold-thrust belt within the eastern Warburton Basin marks the continuation of the curved Delamerian Orogen into the Thomson Orogen. This oroclinal structure may have developed in the Early Devonian in response to dextral transpression along the northern boundary of the Delamerian Orogen. Our results provide a demonstration for the complex interactions that can take place during the evolution of convergent plate boundaries, involving deformation in the fold-thrust belt, development of sedimentary basins, and oroclinal bending.

A possible Mesozoic-Cenozoic trajectory for the North American craton is outlined from latitude changes of the craton derived from a revised apparent polar wander path, and from westward movement of the craton based on the assumption that Africa has been the least mobile continent geographically since the latest Paleozoic. During each of five time intervals that span 220 million years, the craton trajectory had a different vector. Each vector appears to be reflected in the Canadian Cordillera by the dominant style and orientation of structures formed during that interval. For much of the past ~ 220 million years, the ~meridionally-oriented western margin of the Pangea-Laurasia-North America Plate has been the site of arc magmatism where weak arc/back arc lithosphere, sandwiched between strong ocean-floor and craton lithospheres at times coupled across convergent or transform plate boundaries, focused and recorded strain. When the craton apparently moved due westward, between ~180–160 Ma and ~120–60 Ma, the dominant structures formed then record orogen-normal compression and were accompanied by orogeny. Structures formed during the earlier episode are mainly in the eastern and interior Cordillera and their formation shortly followed or coincided with accretion of most terranes to the craton margin. In the later episode, compressional structures span the entire Cordillera, which emerged as a tectonic and physiographic entity. Before and between these intervals, when the craton apparently moved mostly northwestward, mainly geological and paleomagnetic considerations indicate some terranes moved southward (sinistrally) relative to the craton. After ~60 Ma, southwestward movement of the craton was concurrent with large northward (dextral) strike-slip faults that disrupted the newly-established ancestral Cordillera. The coincidence between the age of structures that record dominant orogen-normal compression at times when the craton apparently moved due westward, and orogen-parallel displacements when the craton had either northward or southward components of motion, suggests the craton, acting as a “Continental Bulldozer”, was the primary driver of Cordilleran deformation and orogenesis.

The effects of initial rift inversion over the geometry of a far-foreland intracratonic fold-and-thrust belt are investigated. A total of 25 seismic reflection lines and stratigraphic data from 9 wells are used in association to digital elevation and field geological data, to investigate the geometric relationship between shallow thrust development and initial positive inversion of buried rift faults in a cratonic environment, where inversion tectonics is not common. The study case is conducted in the meeting region of the opposed-verging Brasilia and Aracuai foreland fold-and-thrust Neoproterozoic belts, located in central Brazil, formed in the first stages of West Gondwana amalgamation. Seismic reflection sections are used to map buried paleorift faults and trust ramps. The best 5 sections are also interpreted in detail in terms of fold and thrust geometry and their relationship to the inverted rifts is analyzed. They show high correlation between shallow fold-and-thrust geometry and the shortening of synrift strata, caused by rift inversion. Results indicate that initial positive rift fault reactivation exerts a determinant control over the locus of thrust ramp nucleation, by causing syn-rift strata to overfold and drape fold. The passive folding propagates upwards forming gentle folds in the decollement plane, where thrust ramps tend to nucleate. Back-thrust-forethrust pairs tend to form over elevated horsts, where higher topographic plateaus are preserved. Multiple thrusting and lower relief occur over buried rifts with multiple inverted faults. Strata over non-rifted basement remain practically unaffected by thrusting and folding. Moreover, the development of thrust salients and recesses are demonstrated to be conditioned by the morphology of buried rifts. The study also contributes with a more precise mapping of the buried rift system and thrust system in the area, and brings new insights about the structural evolution of the Brasiliano-Pan Africano orogeny affecting the Sao Francisco craton basement and covers.