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The western margin of the Caribbean Plate is a typical example where oceanic and continental terranes have amalgamated by subduction, collision, and strike-slip processes. The boundaries between these blocks, as well as their tectonostratigraphic records, are generally covered by younger deposits and dense tropical vegetation, which may hamper reconstructing the accretionary evolution of the convergent margin. In that context, the study of overlap sedimentary assemblages represents an important tool to constrain the accretion timing of terranes. In northern Central America, the geology of the suture zone between the Chortis Block and the exotic Siuna Intraoceanic Arc indicates that the two terranes were assembled together during a Hauterivian arc-continent collision (approximately 134–131 Ma). The exotic origin of the intraoceanic arc is based on the nature of metamorphic blocks within and the kinematics of the Siuna Serpentinite Melange. The short duration of the collision event is suggested by coeval exhumation of the Siuna Serpentinite Melange and Chortis-derived coarse sedimentation (El Amparo Formation) along the suture zone, rapidly followed by onset of pelagic sedimentation (Rio Matis Formation). Although the collision appears to have been short lived and preserved only in the suture zone, postcollisional extension affected intra-arc to back-arc settings of the Chortis Block and led to the formation of kilometer-thick extensional basins. We envisage that the convergent margin inboard of SW Mexico—represented by the fringing Guerrero Intraoceanic Arc and the Mixteca continental terrane—underwent similar postcollisional extension, whereas the western margin of the proto-Caribbean oceanic realm experienced onset of WSW dipping subduction beneath the accreted Siuna Intraoceanic Arc.

Magnetotelluric surveys revealed high‐conductivity layers in the lower crust beneath Tibet and in the shallow part of the upper mantle relevant to continental collision extending to the Dabie‐Sulu ultrahigh‐pressure metamorphic (UHPM) belts of eastern China, which have been interpreted by the presence of aqueous fluids/partial melts or hydrous phases. However, these explanations are not consistent with their petrological features and seismic properties. Hydrogen‐bearing omphacite could be a probable candidate to explain such high‐conductivity anomalies due to its high water‐partitioning coefficient versus coexisting garnet in eclogite. In this study, we investigated electrical conductivities of Fe‐free and Fe‐bearing omphacite as a function of water content (0.005–0.122 wt.%) at 3 GPa and 500–1300 K. Our results show that water significantly enhances the electrical conductivity of omphacite, while iron facilitates conductivity by accelerating hydrogen diffusivity and lowering its activation enthalpy. Assuming a heat flow of 70 mW/m2, the high electrical anomalies observed beneath the Dabie‐Sulu UHPM belts and the Tibetan Plateau can be reasonably explained by omphacite containing 0.07 wt.% water since water content higher than 0.07 wt.% in omphacite was frequently reported in naturally collected eclogite.

To understand the relationships between eclogite-facies mineral assemblages, deformation microstructures, and the seismic properties of subducting oceanic crust, eclogites from the Yuka terrane, No...

Studies of the high-pressure (HP) As Sifah eclogites in the NE Saih Hatat window, Oman, have used different combinations of radiometric dating results (Ar/Ar, Sm-Nd vs. U-Pb, Rb-Sr) to interpret disparate tectonic models for the timing, geometry, and cause of continental subduction – including its relationship to the Samail Ophiolite. To determine the timing of continental subduction, we coupled petrochronological analyses of major (garnet) and accessory phases (zircon, rutile) from the highest-grade metamorphic rocks (As Sifah eclogites) in the Saih Hatat. Early Permian (283.8±0.7 Ma) tuffaceous zircon cores are consistent with earlier interpretations that the As Sifah rocks were sourced from a distal portion of the Arabian continental margin. Data from a range of bulk compositions and metamorphic assemblages consistently suggest a single metamorphic event, with garnet growth from ∼81–77 Ma – though with slight, consistent offsets in the timing of metamorphic (re)crystallization between different lithologies. These new data confirm previous interpretations for continental HP metamorphism in a single NE-dipping subduction zone beneath the obducted Samail Ophiolite; there is no robust evidence for a ∼110 Ma event or for SW-dipping subduction beneath the Arabian plate. Combined with other constraints, our data suggest that the As Sifah unit was subducted at rates similar to other small continental HP bodies, followed by two stages of cooling and exhumation – likely associated with the dragging to mantle depths by a mafic root, an initial phase of rapid exhumation from mantle depths, and a lengthy residence (≤40 My) in the lower to middle crust.

International audience; We developed a 2D numerical model that simulates the evolution of a subduction in order to analyze which different metamorphic facies and deformation fabrics can be recorded within a subduction complex and whether the subduction velocity can influence their distribution. Regions with pressure and temperature (P-T) conditions characteristic of different metamorphic facies have been explored in the different domains of the subduction system to verify the existence of associations that may result as diagnostic of specific areas of the subduction system at different times. Distribution patterns of strain rates and relative deformation fabrics have also been investigated to verify whether they can be recorded under different metamorphic facies conditions. Our results show that three domains characterized by contrasting metamorphic conditions can be simultaneously observed in different regions of the subduction complex, in contrast with the widespread idea that different metamorphic series are representative of peculiar geodynamic scenarios, but in agreement with the commonly observed coexistence of contrasted P-T conditions in orogenic belts. In addition, we verified that mylonitic fabrics can develop more frequently in metamorphic facies characterized by high Pressure/Temperature (P/T) ratios, while coronitic fabric can be better preserved in metamorphic facies with low-to-medium P/T ratios

Hydrous phases have been identified to be a significant component of martian mineralogy. Particularly prehnite, zeolites, and serpentine are evidence for low‐grade metamorphic reactions at elevated temperatures in mafic and ultramafic protoliths. Their presence suggests that at least part of the martian crust is sufficiently hydrated for low‐grade metamorphic reactions to occur. A detailed analysis of changes in mineralogy with variations in fluid content and composition along possible martian geotherms can contribute to determine the conditions required for subsurface hydrous alteration, fluid availability and rock properties in the martian crust. In this study, we use phase equilibria models to explore low‐grade metamorphic reactions covering a pressure‐temperature range of 0‐0.5 GPa and 150‐450 °C for several martian protolith compositions and varying fluid content. Our models replicate the detected low‐grade metamorphic/hydrothermal mineral phases like prehnite, chlorite, analcime, unspecified zeolites, and serpentine. Our results also suggest that actinolite should be a part of lower‐grade metamorphic assemblages, but actinolite may not be detected in reflectance spectra for several reasons. By gradually increasing the water content in the modeled whole rock composition, we can estimate the amount of water required to precipitate low‐grade metamorphic phases. Mineralogical constraints do not necessarily require an elevated geothermal gradient for the formation of prehnite. However, restricted crater excavation depths even for large impact craters are not likely sampling prehnite along colder gradients, either suggesting a geotherm of ~ 20 °C/km in the Noachian or an additional heat source such as hydrothermal or magmatic activity.

Exhumation of the high‐grade metamorphic Seve Nappe Complex and its emplacement between lower‐grade nappes has been related to wedge extrusion in the central Scandinavian Caledonides. To test this ...

Like many other mountain belts, the metamorphic core or hinterland of the Brooks Range fold and thrust belt in Arctic Alaska is characterized by multiply deformed and polymetamorphosed rocks whose ...

The Eoarchean Isua supracrustal belt (ISB) has been interpreted as one of the earliest records of subduction processes, leading to the conclusion that a plate tectonic geodynamic system was likely operating since the early Archean. However, proposed tectonic models remain difficult to evaluate as our understanding of the metamorphic and structural evolution remains fragmentary. Here, we present a metamorphic study of the supracrustal rocks of the ISB. We used petrographic and microstructural observations, phase equilibria, isopleth geothermobarometry, and conventional thermometry to explore the prograde, peak, and retrograde metamorphic evolution of the northeastern ISB. Our results show that the ISB records a syn‐tectonic, amphibolite facies metamorphic event (M1) with peak conditions of 550°C–600°C and 0.5–0.7 GPa. M1 was followed by a static, lower amphibolite facies metamorphic event (M2; 3.5 Ga) and the Neoarchean (

Hole BT1B of the Oman Drilling Project provides a continuous sampling from listvenite into the metamorphic sole that preserves the deformation, hydration and carbonation processes of oceanic mantle peridotite at the base of the Samail ophiolite, Oman. We present evidence of multistage brittle deformation in listvenites and serpentinites based on field observations, visual core logging and petrography. About 10 vol% of listvenite and serpentinite in Hole BT1B is composed of cataclasite bands. Cataclasites contain lithic clasts of listvenite with spheroidal, zoned magnesite and quartz, and fragments of chalcedony-carbonate veins ¬¬that elsewhere crosscut listvenite — showing that cataclasis post-dates listvenite formation. Locally the cataclasites are reworked and cut by thin, sharp faults, pointing to repeated reactivation of brittle structures. SEM-EDS mapping shows that cataclasis was related to silica cementation and/or dissolution of carbonate. Dolomite veins crosscut cataclasites and breccias, suggesting that part of the Ca gain in BT1B is related to late fluids after listvenite formation. These results indicate a multistage tectonic overprint after peridotite carbonation and listvenite formation, which may be related to the tectonic history of the deformed continental margin under the ophiolite. These relatively late brittle structures should be excluded when trying to understand the carbonation of peridotite to listvenite.

The exercise of paleogeographic/tectonic reconstruction of past orogenic belts is a complex task that includes the interpretation and integration of multi-technique approaches such as basin tectonics, structural geology, petrology, geochemistry, geochronology, and geodynamics. Proterozoic geologic records are fragmented and incomplete, which make efforts to reconstruct paleogeography and orogenic processes even more challenging. Therefore, for our understanding of the tectonic evolution of past orogenic systems to advance, it is essential that any existing model, including the ones proposed by Heilbron and Valeriano (2020, https://doi.org/10.1029/2019tc005897), are repeatedly exposed to debate and testing. In this reply we address the points raised by Heilbron and Valeriano in order to clarify the scientific foundations of our tectonic interpretation for one of the Neoproterozoic Brasiliano/Pan-African orogens in South America (the Central Ribeira Belt), presented in Meira, Garcia-Casco, Hyppolito, et al. (2019, https://doi.org/10.1029/2018TC004959). We also evaluate the proposed paleogeographic reconstructions for this part of West Gondwana and conclude that an intracontinental model better explains the currently available data and observations, including the space problem pointed out in recent publications, and that existing geochemical and geochronologic data by themselves are not conclusive with respect to an unequivocal tectonic environment., This research was financially supported by São Paulo Research Foundation (FAPESP Grants, #2012/154627 and #2016/061146), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq Gran t, #404767/20168), and CIC (University of Granada). Renato Paes de Almeida, Haakon Fossen, Carolina Cavalcante, Renata Schmitt, Carlos Ganade, and Guiseppe de Toni are fully acknowledge for fruitful discussions

The spectacular kilometer‐thick Funzie Conglomerate is a deformed and metamorphosed high‐energy sedimentary deposit that occurs in Shetland (Scottish Caledonides). Its age and tectonic significance in relation to early Ordovician (485‐475 Ma) and late Ordovician (450‐445 Ma) accretionary orogenic events and the culminating Silurian (430‐425 Ma) continental collision and closure of the Iapetus Ocean have hitherto been unknown. U‐Pb zircon dating indicates that the clast population of the conglomerate was derived from easterly sources comprising Neoproterozoic metasedimentary rocks and the northern extension of the Ordovician‐Silurian Midland Valley Arc that formed during Iapetus closure. A lower age limit of 440 Ma is indicated by the ages of the youngest matrix detrital zircon grains and the youngest granitic clast. Deformation and metamorphism of the conglomerate is attributed to sinistrally oblique extension at c. 430 Ma that excised at least 10 km of crustal section. Sedimentation of the conglomerate is therefore constrained to a 10 myr time span (440‐430 Ma). The tectonic setting is interpreted as a syn‐orogenic basin that received detritus from, and was buried by, advancing thrust nappes during the Early Silurian collision of Laurentia and Baltica. Tectonic burial was followed rapidly by ductile deformation during oblique extensional unroofing of the metamorphic pile, and accounts for preservation of the Funzie Conglomerate as a rare example of a syn‐orogenic basin within the metamorphic hinterland of the North Atlantic Caledonides

Characterizing the lithology, age, and physical-chemical properties of rocks and sediments in the Earths upper crust is necessary to fully assess energy, water, and mineral resources and to address many fundamental questions in the Earth sciences. Although a large number of geological maps, regional geological syntheses, and sample-based measurements have been produced, there is no openly available database that integrates rock record-derived data while facilitating large-scale, quantitative characterization of the volume, age, and material properties of the upper crust. Here we describe Macrostrat, a relational geospatial database and supporting cyberinfrastructure that is designed to enable quantitative spatial and geochronological analyses of the entire assemblage of surface and subsurface sedimentary, igneous and metamorphic rocks. Macrostrat now contains general, comprehensive summaries of the age and properties of 33,903 lithologically and chronologically-defined geological units distributed across 1,474 regions in North and South America, the Caribbean, New Zealand, and the deep sea. Sample-derived data, including fossil occurrences in the Paleobiology Database, more than 180,000 geochemical and outcrop-derived measurements, and more than 2.1 million bedrock geologic map units from over 170 map sources, are linked to specific Macrostrat units and/or lithologies. Macrostrat has generated numerous quantitative results and its data infrastructure is being used in several independently developed mobile applications. However, it is necessary to expand geographic coverage and to refine age models and material properties to arrive at a more precise characterization of the upper crust globally.

Detrital zircon studies can suffer from selective loss of provenance information due to U-Pb age discordance, metamictization, metamorphic overprinting and fluviatile transport processes. The relationship between isotopic composition and zircon grain shape, and how grain shape is modified during transport, is largely unknown. We combine X-ray tomography with U-Pb geochronology to quantify how fluvial transport affects 3-D zircon shape, detrital age signature, and grain density along the Murchison River, whose catchment comprises Eoarchean to Early Paleozoic source rocks in Western Australia. We acquired tomographic volumes and isotopic data from 373 detrital zircons to document changes in size, shape and density in transport direction, and explore how grain shape, age spectra and the proportion of discordant material vary along the channel. Results show that shape characteristics are sensitive to transport distance, stream gradient, proximity to source material, and whether the source consists of primary or recycled zircons. With increasing transport distance, grain lengths decrease more than their widths. Furthermore, the loss of metamict grains occurs at a near constant rate, resulting in a linear increase of mean calculated zircon density by ca. 0.03 g/cm3 per 100 km transport distance. 3-D grain shape is therefore strongly linked to detrital age signature, and mean grain density is a function of the absolute transport distance. 3-D shape characteristics provide valuable information on detrital zircon populations, including the interaction between source materials with fluvial transport processes, which significantly affects preservation bias and, by inference, the representativeness of the sampled data.

Lusi is a sediment‐hosted hydrothermal system featuring clastic‐dominated geyser‐like eruption behavior in East Java, Indonesia. We use 10 months of ambient seismic noise cross correlations from 30 temporary seismic stations to obtain a 3‐D model of shear wave velocity anomalies beneath Lusi, the neighboring Arjuno‐Welirang volcanic complex, and the Watukosek fault system connecting the two. Our work reveals a hydrothermal plume, rooted at a minimum 6 km depth that reaches the surface at the Lusi site. Furthermore, the inversion shows that this vertical anomaly is connected to the adjacent volcanic complex through a narrow (~3 km wide) low velocity corridor slicing the survey area at a depth of ~4–6 km. The NE‐SW direction of this elongated zone matches the strike of the Watukosek fault system. Distinct magmatic chambers are also inferred below the active volcanoes. The large‐scale tomography features an exceptional example of a subsurface connection between a volcanic complex and a solitary erupting hydrothermal system hosted in a hydrocarbon‐rich back‐arc sedimentary basin. These results are consistent with a scenario where deep‐seated fluids (e.g., magmas and released hydrothermal fluids) flow along a region of enhanced transmissivity (i.e., the Watukosek fault system damage zone) from the volcanic arc toward the back arc basin where Lusi resides. The triggered metamorphic reactions occurring at depth in the organic‐rich sediments generated significant overpressure and fluid upwelling that is today released at the spectacular Lusi eruption site.

The Phulad Shear Zone (PSZ) in northwestern India demarcates the boundary between Grenvillian-age para-metamorphics of the South Delhi Fold Belt (SDFB) to the east and variably deformed Neoproterozoic granitoids of the Marwar Craton to the west. In calcareous and quartzofeldspathic mylonites in and around Phulad, the shear zone is characterized by steep SE-dipping mylonitic fabric and a steep oblique stretching lineation. The shear zone is developed in a ductile regime with top-to-the-west reverse sense of movement coupled with pronounced flattening across the PSZ. MnNCKFMASH Pressure-Temperature pseudosection analysis of closely-spaced specimens of garnet-bearing mica schists reveal that the stabilization of syn/post garnet porphyroblasts in the hanging wall experienced near-isothermal decompression followed by cooling in the retrograde arm of a clockwise P-T path. The retrieved P-T paths are consistent with reverse motion of SDFB mica schist over the cratonic foreland. U-Th-Pb (total) monazite age determinations in hanging wall mica schists indicate that reverse motion on the PSZ occurred at 810±6 Ma. The pre-shearing Grenvillian-age (~970 Ma) metamorphic monazites of the SDFB occur as embayed cores, in the interiors of younger monazite grains. Intense high temperature deformation and the emplacement of mica-bearing pegmatites during reverse shearing caused recrystallization of monazites by dissolution-precipitation, mantling older monazites in the hanging wall SDFB schists. It is suggested that the PSZ may represent a terrane boundary shear zone along which the Greater India landmass accreted with the Marwar Craton at ~810 Ma.

The eastern terminations of the Himalayan orogeny, named Namche Barwa, are considered a vital natural laboratory in the Tibetan plateau for geodynamics due to its distinctive geological and geomorphological characteristics. Magnetotelluric (MT) data measured at 83 sites around the Namche Barwa are imaged by three-dimensional (3D) inversion to better reveal the crustal structure of the eastern Himalaya. The results show a complex and heterogeneous electrical structure beneath the Namche Barwa. The electrical conductors distributed in the middle and lower crust around the Namche Barwa provide additional evidence for the “crustal flow” model if they are considered as some parts of the flow in a relatively large-scale region. The near-surface resistivity model beneath the inner part of Namche Barwa conforms with the locations of hot spring and fluid inclusions, the brittle–ductile transition and the 300 °C–400 °C isotherm from previous hydrothermal studies. Relatively resistive upper crust (>800 Ωm) is underlain by a more conductive middle to lower crust (

South central Pyrenean foreland basin fill preserves the eroded remnants of the early stages of fold-thrust belt evolution and topographic growth. Specifically, the Eocene Hecho Group in the Ainsa Basin contains a succession of turbiditic channels and levees deposited in the transition zone between the fluvial-deltaic and deep marine depozones. Detailed isotopic provenance analyses allow for the reconstruction of sediment sources of the ancient sediment routing systems. This study presents 2332 new detrital zircon (DZ) U-Pb ages and 246 new DZ double-dated (U-Th)/(He-Pb) ages from 19 turbiditic and fluvio-deltatic sandstones in the Ainsa Basin. These data indicate a progressive provenance shift from Cadomian/Caledonian plutonic and metamorphic rocks of the eastern Pyrenees to Variscan plutonic rocks in the central Pyrenees. Minor sediment contributions from sources located to the S and SE of the basin are seen throughout the section. New DZ (U-Th)/He results identify four main cooling events: Pyrenean orogenesis (~56 Ma), initial basin inversion (~80 Ma), Cretaceous rifting (~100 Ma), and pre-Mesozoic cooling ages related to earlier tectonic phases. This study imposes new constraints on the paleogeographic evolution of the Pyrenees and illustrates that high-frequency fluctuations in sediment delivery processes and sediment routing introduce superimposed noise upon the basin-scale long-term provenance evolution during orogenesis.

The temperature response to stress changes of rocks is key to understanding temperature anomalies in geoscience phenomena such as earthquakes. We developed a new hydrostatic compression system in which the rock specimen center can achieve adiabatic conditions during the first ~10 s following rapid loading or unloading, and systematically measured several representative sedimentary, igneous and metamorphic rocks sampled from two seismogenic zones [the Longmenshan Fault Zone in Sichuan, and the Chelungpu Fault Zone (TCDP Hole-A) in Taiwan], and several quarries worldwide. We built a finite element model of heat conduction to confirm the measured results of temperature response to stress changes of rocks. The results show that: (1) the adiabatic pressure derivative of the temperature (β) for most crustal rocks is ~1.5 mK/MPa to 6.2 mK/MPa, (2) the temperature response to stress of sedimentary rocks (~3.5-6.2 mK/MPa) is larger than that of igneous and metamorphic rocks (~2.5-3.2 mK/MPa), and (3) there is good linear correlation between β (in mK/MPa) and the bulk modulus K (in GPa): β=(-0.068·K + 5.69) ± 0.4, R2 = 0.85. This empirical equation will be very useful for estimating the distribution of β in the crust, because K can be calculated when profiles of crustal density (ρ) and elastic wave velocities (Vp, Vs) are obtained from gravity surveys and seismic exploration

New single crystal 40Ar/39Ar and apatite fission track ages from the Kanchenjunga region of far east Nepal yield insight into the timing of assembly of the Himalayan mid-crust and the mechanisms that controlled its exhumation. The 40Ar/39Ar data are compared with new U(Th)/Pb zircon and monazite intrusive crystallization ages and existing metamorphic monazite ages from across the study area to test for internal consistency and potential excess Ar contributions. This new dataset, which significantly enhances the density and spatial coverage available from the region, shows that inferred thrust-sense discontinuities within the now-exhumed former midcrustal rocks exposed therein must have ceased motion by ca. 12 Ma. Furthermore, the spatial distribution of ages across the Kanchenjunga region, older ages (ca. 12 – 16 Ma) to the south and north and younger ages (ca. 8 Ma) in the middle portion of the transect, is compatible with simulations of tectonic-enhanced exhumation above a developing duplex system in nearby Bhutan.

The timing, kinematics, and mode of exhumation within the Alpujarride Complex, the largest tectonic unit of the Alboran Domain, are controversial. Alternative tectonic models include synorogenic exhumation during pre-Miocene crustal thickening, intraorogenic exhumation during repeated phases of contraction and extension, and late orogenic exhumation during early Miocene crustal thinning. New structural and petrographic relationships documented in this study support the latter model: subhorizontal foliations, stretching lineations, and recumbent folds are associated with early Miocene high-temperature decompressional metamorphism and vertical condensation of the metamorphic sequence. Relict isograds associated with high-pressure metamorphism and burial are systematically overprinted by isograds associated with high-temperature metamorphism and rapid decompression. During the early stages of extensional exhumation and growth of sillimanite, ENE directed shear (D2) overprinted thrusts and foliations associated with crustal thickening (D1). During the later stages of extensional exhumation and growth of andalusite, from ductile to semibrittle conditions, north directed shear (D3) produced kilometer-scale recumbent folds that refold isograds. Stretching lineations characterize superposed directions of orogen-parallel (L2) and later orogen-perpendicular (L3) shear associated with a rapid temporal transition in the kinematics of extensional exhumation. During the final stages of crustal thinning and cooling, ductile structures (D2/D3) were cut by brittle low-angle normal faults (D4).

To characterize the metallogenic environment of a typical vein-type uranium deposit, samples from diabase dykes, alteration zones including metamorphic diabase and uranium ore, and granites were systematically investigated for six boreholes from southeastern China. Rock magnetic results indicate that coarse-grained magnetites (pseudosingle domain, PSD, and multidomain, MD) are dominant magnetic carriers in diabase. In contrast, the uranium ore is dominated by fine-grained magnetites (superparamagnetic, SP, and single-domain, SD). The concentration of magnetic particles in fresh granites is low. Magnetic properties of metamorphic diabases exhibit much greater variability of magnetic properties and higher degrees of sulfuration than unaltered diabase and granite, due to contact metasomatism and reduction effects close to the vein. Compared with diabase, magnetic remanence of the uranium ore is much lower, but displays much higher stability. The Koenigsberger ratio Q peaks in the uranium ore with a value of ∼1.00. Using the systematic rock magnetic results to constrain the interpretation, the contribution of the intersection zone of diabase dyke and silicified fault to magnetic anomalies was further modeled, and the effects of the ore body are significant for magnetic exploration. Overall, rock magnetic investigations of vein-type uranium deposit provide a better understanding of the interactions between different rock types, and further facilitate regional magnetic surveys on the ground.

This work was jointly funded by the Young Scientist Fund of the National Natural Science Foundation of China (grant 41402177) and the Fundamental Research Funds for the Central Universities (2652014004). Our field work was supported by a project issued by the China Geological Survey (CGS): The integrated geological survey on the west part and central uplift of Qiangtang Block (grant 12120115026901).

The Yuli metamorphic belt has been the topic of petrological and geochronological studies for over 40 years and has been interpreted as a Cretaceous melange. Our study utilizes zircon U-Pb dating of schist and exotic blueschist blocks in the Yuli belt. These new ages indicate that these metamorphic rocks are actually middle Miocene in age and may represent the deeper structural levels of an accretionary prism. Several distinctive detrital zircon U-Pb age populations are recognized from 14 siliceous schists of melange-hosted rocks that are similar in age population to the Cretaceous, Eocene-Oligocene, and Miocene strata of Taiwan. The wide range of ages is interpreted as a product mixing of various sedimentary strata prior to metamorphism. Three blueschists of a volcanic-arc protolith enclosed within the host rocks yield crystallization ages of 15.4 ± 0.4, 15.5 ± 0.3, and 16.0 ± 0.2 Ma based on zircon U-Pb dating. In consideration of the new data regarding the Cretaceous-Miocene host rocks and the middle Miocene exotic blueschist blocks, it strongly suggests that the Yuli belt formed at deeper levels of an accretionary wedge during subduction of South China Sea oceanic crust at the middle-late Miocene. Subsequently, the rapid uplift of the metamorphic belt was probably related to doubly vergent wedge extrusion due to the Pliocene arc-continent collision.

Recent Oklahoma seismicity shows a regional correlation with increased wastewater injection activity, but local variations suggest that some areas are more likely to exhibit induced seismicity than others. We combine geophysical and drill hole data to map subsurface geologic features in the crystalline basement, where most earthquakes are occurring, and examine probable contributing factors. We find that most earthquakes are located where the crystalline basement is likely composed of fractured intrusive or metamorphic rock. Areas with extrusive rock or thick (>4 km) sedimentary cover exhibit little seismicity, even in high injection rate areas, similar to deep sedimentary basins in Michigan and western North Dakota. These differences in seismicity may be due to variations in permeability structure: within intrusive rocks, fluids can become narrowly focused in fractures and faults, causing an increase in local pore fluid pressure, whereas more distributed pore space in sedimentary and extrusive rocks may relax pore fluid pressure.

The Cenozoic Xuelong Shan antiformal dome is located along the northern segment of the Ailao Shan-Red River shear zone in Yunnan, China. Subhorizontal foliation in the gneiss core is recognized, representing a broad top-to-NE shear initiated under amphibolite facies conditions and propagating into greenschist facies in the mantling schist and strike-slip shear zone. Microfabrics of crystallographic-preferred orientations (CPOs) in quartz suggest that the deformation temperatures increased with increasing structural depth from the upper crust (300-500 degrees C) in the mantling schist to the midcrust (15 km or more, 650 degrees C) in the gneissic core. This trend is mirrored by variations in the metamorphic grade of the syn-kinematic mineral assemblages and microstructures, which range from garnet+amphibole+biotite+sillimanite+rutile+feldspar in the core to garnet+staurolite+biotite+epidote+muscovite within the limb units. The dome experienced the following deformation history: (1) a broad top-to-NE shear in the subhorizontal foliation of the gneiss core during the first stage of deformation (D1); (2) opposing reverse-sense shear along the two schist limbs of the dome during contraction-related doming (D2-D3); (3) sinistral strike-slip shearing within the eastern limb (D4); and (4) extensional deformation (D5). The structural-thermal patterns suggest the antiformal dome formation was roughly coeval with top-to-NE ductile shearing in the midcrust of Tibet at 32 Ma or earlier. A major implication is that there was a phase of contractional ductile deformation in the region prior to the initiation of strike-slip deformation.

The Esfandagheh region of the Zagros Orogenic Belt is an ideal area to address many aspects of continental convergence between Arabia and Eurasia, including incorporation of Late Neoproterozoic (Ediacaran) basement, subduction-related magmatism, and the formation of HP/LT rocks. The rock units exposed here represent a presumably Jurassic magmatic arc within the Sanandaj-Sirjan Zone (SSNZ), remnants of oceanic lithosphere, blueschist- and greenschist-facies rocks, and a distinct group of poorly characterized rocks. U-Pb ages define four populations, related to Paleoproterozoic, Ediacaran, Carboniferous, and Jurassic magmatic events. U-Pb ages of ∼1.8–1.7 Ga for a pegmatite represent the first report of Paleoproterozoic rocks in Iran. Zircon U-Pb ages from the SSNZ provide evidence for Ediacaran (547 Ma), Carboniferous (326–312 Ma), and Jurassic (194–186 Ma) magmatic activity. Zircons from the Haji-Abad ophiolites yielded Jurassic ages. The new Rb-Sr results from white micas provide indications of a poorly constrained >85 Ma high-pressure metamorphic history. Rb-Sr ages of two chlorite-epidote-actinolite schists indicate that greenschist-facies P-T conditions had already been attained around 130–125 Ma. The new results are consistent with a model in which the closure of the Esfandagheh Ocean and the subsequent collision between Arabia and Iran led to incorporation of Paleoproterozoic and Cadomian rock units and tectonic juxtaposition of all lithotectonic elements, from oceanic lithosphere to continental crust, along the Main Zagros Suture Zone.

Subduction erosion is confirmed as a crucial geodynamic process of crustal recycling based on geological, geochemical, and geophysical observations at modern convergent plate margins. So far, not a single metamorphic record has been used for constraining a general tectonic evolution for subduction erosion. Here we first revealed metamorphic records for a subduction erosion process based on our study of the Late Paleozoic garnet-staurolite-muscovite schists in the central Qiangtang block, Tibet. Provenance analyses suggest that the protoliths of garnet-staurolite-muscovite schists have the Northern Qiangtang-affinity and were deposited in an active continental margin setting. Mineral inclusion data show that the early metamorphic stage (M1) recorded blueschist facies pressure-temperature (P-T) conditions of 0.8–1.1 GPa and 402–441°C, indicating that a part of the material from the overriding plate had been abraded into the subduction channel and undergone high-pressure/low-temperature metamorphism. The peak metamorphic stage (M2) recorded amphibolite facies P-T conditions of 0.3–0.5 GPa and 470–520°C. The 40Ar/39Ar cooling ages (263–259 Ma) yielded from muscovite suggest the amphibolite facies metamorphism (>263 Ma) occurred at oceanic subduction stage. The distinctly staged metamorphism defines a clockwise and warming decompression P-T-t path which reveals an underplating process following the early subduction erosion. During the tectonic process, the eroded low-density material escaped from the cold subduction channel and rise upward into the warm middle-lower crust of the upper plate, undergoing amphibolite facies metamorphism. Our new results revealed a complete evolutional process from the early subduction erosion to the subsequent underplating during the northward subduction of the Paleo-Tethys Ocean.

Long-lived exterior accretionary orogeny shapes tectonothermal evolution of the peripheral building blocks of supercontinents and leads to considerable crustal growth. However, such accretionary orogeny has only been locally recognized for the Rodinia supercontinent. Here a suite of newly discovered mid-Neoproterozoic high-grade metamorphic rocks in the northern Tarim Craton, NW China, are used to test the exterior accretion hypothesis for Rodinia. These rocks occur as dark-colored mafic and calc-silicate boudins in impure marbles and mica schists. Geochemical data suggest a protolith of arc-related basalts metasomatized by Ca-rich fluids. Mineral assemblages, phase diagram modeling, and mineral compositions for a garnet pyroxenite and a garnet clinopyroxene gneiss reveal upper amphibolite to high-pressure granulite facies peak metamorphism (660–700°C, 11–12 kbar) following a counterclockwise P-T path, which is characterized by prograde burial and heating, followed by near-isothermal burial and retrograde exhumation and cooling. This P-T path is interpreted to have recorded crustal thickening of an earlier magmatic arc transformed to a fore arc by subduction erosion and subsequent burial along bent isotherms near the subduction channel. All studied samples record ca. 830–800 Ma metamorphic zircon U-Pb ages, which probably date the early exhumation and cooling according to Ti-in-zircon temperatures, zircon rare earth element patterns, and Hf isotopes. This is the first mid-Neoproterozoic P-T-t path in Tarim, and it provides metamorphic evidence for a mid-Neoproterozoic advancing-type accretionary orogeny, which is coeval with the initial breakup events of Rodinia and thus links Tarim to the circum-Rodinia accretion system, supporting the peripheral subduction model.

The Himalayan orogen represents a ‘‘Composite Orogenic System’’ in which channel flow, wedge extrusion, and thrust stacking operate in separate ‘‘Orogenic Domains’’ with distinct rheologies and crustal positions. We analyze 104 samples from the metamorphic core (Greater Himalayan Sequence, GHS) and bounding units of the Annapurna-Dhaulagiri Himalaya, central Nepal. Optical microscopy and electron backscatter diffraction (EBSD) analyses provide a record of deformation microstructures and an indication of active crystal slip systems, strain geometries, and deformation temperatures. These data, combined with existing thermobarometry and geochronology data are used to construct detailed deformation temperature profiles for the GHS. The profiles define a three-stage thermokinematic evolution from midcrustal channel flow (Stage 1, >7008C to 550–6508C), to rigid wedge extrusion (Stage 2, 400–6008C) and duplexing (Stage 3

The Hidaka collision zone, where the Kurile and northeastern (NE) Japan arcs collide, provides a useful study area for elucidating the processes of arc-continent evolution and inland earthquakes. To produce an image of the collision structure and elucidate the mechanisms of anomalously deep inland earthquakes such as the 1970 Hidaka earthquake (M6.7), we conducted magnetotelluric observations and generated a three-dimensional resistivity distribution in the southern part of the Hidaka collision zone. The modeled resistivity was characterized by a high resistivity area in the upper crust of the Kurile arc corresponding to metamorphic rocks. The model also showed conductive zones beneath the center of the collision zone. The boundary between the resistive and conductive areas corresponds geometrically to the Hidaka main thrust, which is regarded as the arc-arc boundary. The correspondence supports the collision model that the upper-middle part of crust in the Kurile arc is obducting over the NE Japan arc. The conductive areas were interpreted as fluid-filled zones associated with collision processes and upwelling of dehydrated fluid from the subducting Pacific slab. The fluid flow possibly contributes to over-pressurized conduction that produces deep inland earthquakes. We also observed a significant conductive anomaly beneath the area of Horoman peridotite, which may be related to the uplift of mantle materials to the surface.

Internal heating can cause melting, metamorphism, and crustal weakening in convergent orogens. This study evaluates the role of radiogenic heat production (RHP) in a Neoproterozoic ultrahigh-temperature metamorphic (UHTM) terrane exposed in southern Madagascar. Monazite and zircon geochronology indicates that the Paleoproterozoic Androyen and Anosyen domains (i) collided with the oceanic Vohibory Arc at ~630 Ma, (ii) became incorporated into the Gondwanan collisional orogen by ~580 Ma, and (iii) were exhumed during crustal thinning at 525–510 Ma. Ti-in-quartz and Zr-in-rutile thermometry reveals that UHTM occurred over >20,000 km^2, mostly within the Anosyen domain. Assuming that U, Th, and K contents of samples from the field area are representative of the middle to lower crust during orogenesis, RHP was high enough—locally >5 μW/m^3—to cause regional UHTM in

Taiwan is the result of arc‐continent collision associated with the convergence of the Philippine Sea plate with the eastern Eurasian plate continental margin. The locus of deformation is found in eastern Taiwan in the form of mountain building (Central Range) with underlying thickened lithosphere. Rapid tectonic exhumation in the Central Range has uncovered low‐to‐high‐grade metamorphic rocks marked by steep cleavage. We carried out a crustal seismic anisotropy study across Taiwan, producing a database of over 27,000 local earthquake shear wave splitting measurements. Additionally, we carried out rock physics measurements of metamorphic outcrop samples to quantify shear wave rock anisotropy. We produced a map of station‐averaged splitting measurements across Taiwan. Patterns of fast shear wave directions correlate with tectonic terranes produced by plate convergence. Deformation‐related mineral‐preferred orientation in the metamorphic rocks produces a significant amount of the crustal anisotropy in the Taiwan collision zone.

Rocks exposed in NW India constrain the burial, partial melting, and exhumation history of the Himalayan crust. New microscale and mesoscale structural analysis, combined with pressure-temperature estimates from the Haimanta Group exposed in the Sutlej Valley, indicate that the rocks were folded by two generations of NW trending folds. Barrovian metamorphism culminated at ~30 Ma with staurolite and kyanite overgrowths of F2 folds. Crustal thickening created a metamorphic field gradient that increases from the garnet zone (499 ± 99°C and 4.5 ± 1.4 kbar to 571 ± 92°C and 7.8 ± 1.4 kbar) to the staurolite-kyanite zone (567 ± 105°C and 6.7 ± 1.6 kbar). These data are combined with previous studies to modify a two-stage conceptual model for the thermal and deformation conditions of the middle and upper crust during the Eocene-Miocene, excluding the late Miocene to recent. In the Miocene (~23 Ma), Barrovian metamorphism was overprinted by decompression during coeval south directed extrusion of the Greater Himalayan Series beneath the Sangla detachment in the foreland and doming during top-down-to-the-west displacement along the Leo Pargil shear zone in the hinterland. These data demonstrate that shear zones and detachments, such as the South Tibetan detachment that initially formed during crustal thickening (e.g., Eocene-Oligocene), contributed to the subsequent distribution of rocks that experienced different pressure-temperature-time paths, degrees of partial melting, and exhumation histories during the Miocene.

The chromium isotope compositions of 27 metamorphic mafic rocks with varying metamorphic degrees from eastern China were systematically measured to investigate the Cr isotope behavior during continental crust subduction. The Cr isotope compositions of all samples studied were Bulk Silicate Earth (BSE) like, with δ53CrNIST979 of greenschists, amphibolites, and eclogites ranging from −0.06‰ to −0.17‰, −0.05‰ to −0.27‰, and −0.01‰ to −0.24‰, respectively. The lack of resolvable isotopic variability among the metamorphic rocks from different metamorphic zones indicated that no systematic Cr isotope fractionation was associated with the degree of metamorphism. However, the Cr isotopic variability among homologous samples may have reflected effects induced by metamorphic dehydration with a change of redox state, rather than protolith heterogeneity (i.e., magma differentiation). In addition, the differences in δ53Cr (Δ53CrCpx-Gt) between coexisting clinopyroxene (Cpx) and garnet (Gt) from two garnet pyroxenites were 0.06‰ and 0.34‰, respectively, indicating that significant inter-mineral Cr isotope disequilibria could occur during metamorphism. To provide a basis for comparison with metamorphic rocks and to provide further constraints on the potential Cr isotope heterogeneity in the mantle and in the protolith of some metamorphic rocks, we analyzed mantle-derived chromites and the associated peridotites from Luobusa, and we obtained the following general order: chromite-free peridotites (−0.21‰ to −0.11‰)

A three-dimensional (3-D) electrical resistivity model of Mono Basin in eastern California, unveils a complex subsurface filled with zones of partial melt, fluid-filled fracture networks, cold plutons, and regional faults. In 2013, 62 broadband magnetotelluric stations were collected in an array around southeastern Mono Basin from which a 3-D electrical resistivity model was created with a resolvable depth of 35 km. Multiple robust electrical resistivity features were found that correlate with existing geophysical observations. The most robust features are two 300 ± 50 km3 near-vertical conductive bodies (3–10 Ω m) that underlie the southeast and northeastern margin of Mono Craters below 10 km depth. These features are interpreted as magmatic crystal-melt mush zones of 15 ± 5% interstitial melt surrounded by hydrothermal fluids and are likely sources for Holocene eruptions. Two conductive east dipping structures appear to connect each magma source region to the surface. A conductive arc-like structure (

Thermal emission spectroscopy is used to determine the mineralogy of sandstone and mudstone rocks as part of an investigation of linear spectral mixing between sedimentary constituent phases. With widespread occurrences of sedimentary rocks on the surface of Mars, critical examination of the accuracy associated with quantitative models of mineral abundances derived from thermal emission spectra of sedimentary materials is necessary. Although thermal emission spectroscopy has been previously proven to be a viable technique to obtain quantitative mineralogy from igneous and metamorphic materials, sedimentary rocks, with natural variation of composition, compaction, and grain size, have yet to be examined. In this work, we present an analysis of the thermal emission spectral (~270–1650 cm−1) characteristics of a suite of 13 sandstones and 14 mudstones. X-ray diffraction and traditional point counting procedures were all evaluated in comparison with thermal emission spectroscopy. Results from this work are consistent with previous thermal emission spectroscopy studies and indicate that bulk rock mineral abundances can be estimated within 11.2% for detrital grains (i.e., quartz and feldspars) and 14.8% for all other mineral phases present in both sandstones and mudstones, in comparison to common in situ techniques used for determining bulk rock composition. Clay-sized to fine silt-sized grained phase identification is less accurate, with differences from the known ranging from ~5 to 24% on average. Nevertheless, linear least squares modeling of thermal emission spectra is an advantageous technique for determining abundances of detrital grains and sedimentary matrix and for providing a rapid classification of clastic rocks.

We thank Philippe Olivier for the great attention he paid in reading our work and for the discussion he initiated. P. Olivier has been alarmed by our proposition that some Pyrenean granulites might have been (re)granulitized during the Cretaceous rifting event. In a rigorous scientific approach, this hypothesis has to be envisioned. However, in the paper, we proposed two alternative scenarios: one involving a Cretaceous (re)granulitization and another one implying a succession of metamorphic events with a first Paleozoic High Temperature (HT) metamorphism event responsible for the granulitization, followed by a second HT metamorphism event during the Cretaceous. Our main point here was to put in relation the strikingly similar fields of metamorphisms responsible for the granulitization of the crystalline basement and for the HT metamorphism of the prerift and synrift Mesozoic sedimentary cover. In other words: with temperatures up to 600°C in the metasedimentary cover, we would expect temperatures at least as high as 600°C in the basement. If not, it would mean that the continental crustal basement was already withdrawn from the metamorphic domain at that point. This scenario corresponds in fact to the concept of lateral extraction of the continental crust that we retained from our field constraints and that we defend here.

International audience; Detrital provenance analyses in orogenic settings, in which sediments are collected at the outlet of a catchment, have become an important tool to estimate how erosion varies in space and time. Here we present how Raman Spectroscopy on Carbonaceous Material (RSCM) can be used for provenance analysis. RSCM provides an estimate of the peak temperature (RSCM‐T) experienced during metamorphism. We show that we can infer modern erosion patterns in a catchment by combining new measurements on detrital sands with previously acquired bedrock data. We focus on the Whataroa catchment in the Southern Alps of New Zealand and exploit the metamorphic gradient that runs parallel to the main drainage direction. To account for potential sampling biases, we also quantify abrasion properties using flume experiments and measure the total organic carbon content in the bedrock that produced the collected sands. Finally, we integrate these parameters into a mass‐conservative model. Our results first demonstrate that RSCM‐T can be used for detrital studies. Second, we find that spatial variations in tracer concentration and erosion have a first‐order control on the RSCM‐T distributions, even though our flume experiments reveal that weak lithologies produce substantially more fine particles than do more durable lithologies. This result implies that sand specimens are good proxies for mapping spatial variations in erosion when the bedrock concentration of the target mineral is quantified. The modeling suggests that highest present‐day erosion rates (in Whataroa catchment) are not situated at the range front but around 10 km into the mountain belt.