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Tectonic and surface processes (e.g., erosion) act in concert to denude and flatten elevated topography during and following collisional uplift. In orogens that collapsed rapidly (<10 Myr), the effectiveness and relative contribution of erosion remains poorly understood. Here, we use 1‐D and 2‐D finite‐difference models to test plausible magnitudes of erosion during denudation of the Scandian orogenic wedge, in northern Scotland, which previous work suggests may have been very rapid. Thermochronologic, stratigraphic, and thermobarometric data constrain initial post‐collision uplift rates as well as the cumulative post‐collisional exhumation magnitude. Using these constraints, we consider an idealized orogen subjected to fluvial incision, hillslope diffusion, and subsequent isostatic compensation for a duration of 10 Myr. Using a range of geomorphic parameters, we evaluate whether erosion alone is sufficient to achieve the observed cumulative exhumation. Additionally, we apply a thermal model during the same period to determine the viability of the previous erosion estimates in the presence of a transient geothermal gradient. For most cases with initial uplift rates of 0.5–2.5 mm yr−1, total erosion is insufficient to account for the observed Scandian denudation history, regardless of whether a fixed or transient geothermal gradient is assumed. Average elevations near the crest of the modeled orogen after 10 Myr are >1.4 km, which is inconsistent with the post‐Scandian landscape relief interpreted from the reconstructed depositional surface of the Emsian (407–403 Ma) Old Red Sandstone, Collectively these findings imply a combination of rapid erosion and tectonic denudation likely accomplished the rapid collapse of the Scandian wedge. Plain Language Summary: The destruction of mountain ranges is accomplished by numerous physical processes, which include erosion of the landscape and subsurface deformation of the Earth's crust. In mountains where this destruction occurred very rapidly, such as in northern Scotland, there is poor understanding of the relative effectiveness of each process in wearing mountains down. In this paper, we use computer models to calculate how much erosion might have occurred in the geologically short time frame after the mountains in Scotland stopped growing. These models track the effects of river erosion, hillslope movement, and crustal buoyancy on elevation change after mountain‐building has essentially ceased. We compare the model results to pressure‐temperature‐time data recorded in rocks exposed at the surface today that give us information about how fast the rocks were brought up to the Earth's surface from depth. Our inference based on these models is that erosion alone cannot remove material quickly enough to explain available geologic data, implying the importance of crustal thinning by deformation in the Scottish Highlands. Key Points: Published thermochronologic data for metamorphic rocks of the Scottish Highlands indicate rapid denudation following orogenesisThe models in this work suggest that denudation was not accomplished by surface processes alone, but required additional tectonic processesThis may indicate a role for channelized crustal flow similar to that proposed for the Himalaya and the East Greenland Caledonides [ABSTRACT FROM AUTHOR]

The article reports on science research based on geology which informs about the seismological evidence for the earliest global subduction network with earliest evidence for subduction, which have been localized, does not signify when plate tectonics global phenomenon. Topics include investigated Paleoproterozoic time, for which seismic evidence is available from multiple continents; and high-density seismic array in North China to image the crustal structure that exhibits a dipping Moho.

Greater India comprises a part of the Indian plate that subducted under Asia to help form the Tibetan Plateau. Defining the size of the Greater India is thus a key constraint to model the India‐Asia collision, growth of the plateau, and the tectonic evolution of the Neo‐Tethyan realm. We report Early Cretaceous paleomagnetic data from the central and eastern Tethyan Himalaya that yield paleolatitudes consistent with previous Early Cretaceous paleogeographic reconstructions. These data suggest Greater India extended at least 2,675 ± 720 and 1,950 ± 970 km farther north from the present northern margin of India at 83.6°E and 92.4°E, respectively. An area of lithosphere ≥4.7 × 106 km2 was consumed through subduction, thereby placing a strict limit on the minimum amount of Indian lithosphere consumed since the breakup of Gondwanaland. Plain Language Summary: Greater India is part of the Indian plate, subsequently subducted under Asia, that helped create the Tibetan Plateau. The amount of Greater Indian crust therefore plays a critical role to address key problems in continental geodynamics. To what extent can continental crust be subducted? How much crust was derived from horizontal shortening of existing crust? How much of Tibet was created by subducted buoyant, continental crust? We provide paleomagnetic evidence that defines the minimum size of Greater India. Our data show that a lithospheric area of ≥4.7 × 106 km2 was subducted, which supports the notion that the growth of Tibetan Plateau in the Cenozoic occurred by adding buoyant material to its base. Key Points: Early Cretaceous paleomagnetic data from the central and eastern Tethyan Himalaya yield paleolatitudes of 30.5 ± 4.9 °S and 39.6 ± 7.6 °SGreater India extended 2,675 ± 720 and 1,950 ± 970 km farther north from the present northern margin of India at 83.6 °E and 92.4 °E at ~130 MaAn area of ≥ 4.7 × 106 km2 of Greater Indian lithosphere was consumed by subduction [ABSTRACT FROM AUTHOR]

Understanding the thermal evolution of the Alleghanian orogen in the southernmost Appalachians (southeastern United States) is key to understanding the orogenic collapse and extensional tectonics that led to the breakup of Pangea. Cooling-age contours derived from 40Ar/39Ar ages of hornblende, muscovite, and biotite from granitic plutons and their country rocks show a regional pattern of younging toward the southeast. This cooling-age gradient, along with the distribution of normal faults, discontinuities in metamorphic grade, and rifting of the South Georgia basin suggest that the southernmost Appalachian crystalline rocks between the Brevard fault and the Coastal Plain unconformity were exhumed as the lower plate of an extensional detachment fault system. The Suwannee and Charleston terranes likely preserve part of the upper plate. These features represent the postorogenic collapse of the southernmost Appalachians probably along an extensive detachment fault system in the Permian-Middle Triassic. This episode of extension may have played a crucial role in thinning the continental crust to its current thickness and likely was the first stage of extension that eventually led to the breakup of Pangea and formation of the Atlantic Ocean. [ABSTRACT FROM AUTHOR]

The Neoproterozoic Liujiaping Cu-Zn deposit is a typical VMS (volcanic massive sulfide) deposit in the northwestern Yangtze Block, which is located at the convergent region of different blocks in China. The tectonic setting could provide some implications for the Neoproterozoic tectonic evolution of the Yangtze Block. Both the metallogenic chronology and isotope geochemistry of the Liujiaping deposit are tested. Sulfides and zircons from this deposit were analysed to determine its mineralization age. The sulfide Rb-Sr isotope dating of ores yields an age of 821.0 ± 5.0 Ma (MSWD = 0.2). The zircon U-Pb SIMS dating of volcanics yields as 825.5 ± 5.1 Ma (MSWD = 0.3). These dating results indicate that the metallogenesis is synchronous with the volcanic eruption. The Rb contents of the sulfides range from 0.0714 × 10-6 to 0.7986 × 10-6, the Sr contents range from 0.6002 × 10-6 to 15.49 × 10-6, and the initial Sr isotopic ratios (87Sr/86Sr)i range from 0.70784 to 0.70911, with an average of 0.70815. The Pb isotopic compositions of the ores and volcanics are (206Pb/204Pb) = 16.751-18.051, (207Pb/204Pb) = 15.363-15.597 and (208Pb/204Pb) = 36.885-38.441. These isotopic geochemical characteristics indicate that the ore-forming materials of the Liujiaping deposit might originate from the mixture of continental crust and mantle. Other Meso-Neoproterozoic VMS deposits along the northwestern Yangtze Block are also summarized. It is concluded that the Liujiaping volcanics and other VMS deposits were formed by the partial melting of lower crust during the subduction of oceanic crust, and the northwestern margin of the Yangtze Block was located in an arc setting at ~820 Ma rather than intra-continental rift. [ABSTRACT FROM AUTHOR]

Exhumation of plutonic systems is driven by a range of mechanisms including isostatic, tectonic, and erosional processes. Variable rates of plutonic exhumation in active subduction systems may be driven by idiosyncrasies of regional geology or by first‐order tectonic features. We report new age, isotope, and low‐temperature thermochronology constraints of granitoids from the Hida Mountains of central Japan that constrain the highest rates and magnitude of plutonic rock exhumation within the Japan and one of the highest worldwide. This extreme exhumation is centered on the apex of a lithospheric scale anticlinorium associated with the subduction of the Izu‐Bonin oceanic arc. The spatial and temporal relationship between the exhumation of these Pleistocene plutons and the subducting/accreting Izu‐Bonin oceanic arc links the plate‐scale geodynamics and regional exhumation patterns. Identifying thermochronological anomalies within magmatic arcs provides an opportunity to identify ancient asperities previously subducted and responsible for rapid exhumation rates within ancient subduction systems. Plain Language Summary: Plutonic rocks reach the surface through a variety of geological processes. Generally, this is driven by active tectonic and erosive forces. We provide high‐precision geochronological constraint on the youngest exposed subduction zone plutons found in the Hida Mountains of Japan that are 818.5 ± 9.6 thousand years old. Regionally, the Hida Mountains is identified as a thermochronological "hot spot" where the rocks in the region came to the surface very rapidly within the past ~300,000 years. The exhumation of these plutons was driven by the subduction of the Izu‐Bonin oceanic arc. Key Points: Timing of crystallization and exhumation of the youngest exposed plutons is constrained with high precision analytical techniquesOne of the highest exhumation rates for plutonic rocks worldwide is reportedExhumation of Pleistocene granitoid plutons is driven by subducting Izu‐Bonin oceanic arc [ABSTRACT FROM AUTHOR]

New maps of crustal thickness and Vp/Vs in Alaska and western Canada were obtained using P receiver functions recorded at 198 stations from the USArray Transportable Array and the Alaska Regional Network. Our results indicate that topography and Moho depth are correlated as crustal thickness varies from 28 to 43 km across Alaska. A thick crust occurs under the mountains in the south and north with relatively thin crust in central Alaska. The deepest crustal root beneath the Brooks Range may have lost its buoyancy based on Airy isostasy. In addition, a buoyant upper mantle is required to support the high topography in east central Alaska. Vp/Vs is determined between 1.7 and 1.8 beneath most of Alaska except a high average of 1.9 in the south central region. We attribute this high Vp/Vs to the underplating of Yakutat and Pacific oceanic crust. Plain Language Summary: We have developed the first statewide maps of crustal thickness and Vp/Vs in Alaska and western Canada. The observed crustal thickness generally correlates with surface topography, and the Denali Fault is associated with a sharp step of crustal structure variation. A deep Moho and high Vp/Vs are imaged under southern Alaska following the outline of the subducting Yakutat and Pacific slab, probably caused by the underplated oceanic crust. The thin crust in east central Alaska is not enough to compensate the elevation. A buoyant upper mantle at the northeastern edge of the Yakutat slab is required for maintaining local isostasy. The thickest crust under the Brooks Range overcompensates the elevation, suggesting a densified crustal root. Key Points: The maps of crustal thickness and Vp/Vs are produced in Alaska and western CanadaThe Moho depth in Alaska largely correlates with the topographyHigh Vp/Vs is observed in south central Alaska, probably due to the underplated oceanic crust [ABSTRACT FROM AUTHOR]

Conventional well logs serve as effective tools for estimation of pore pressure (PP), tectonic strain and stress magnitudes in normal and thrust faulted parts of the Upper Assam basin. Several models have been developed for prediction of PP and stress magnitudes over the years. Acquiring tectonic strain in active area enhances the accuracy of in situ stress estimate in the Upper Assam. This paper discusses Eaton's sonic model for PP estimation and assesses stress magnitudes incorporating tectonic strain in poroelastic models. Eaton's exponent is varied from 0 to 3 to get best-fit results for PP prediction validated with available modular dynamic tester and mud weight data. PP is estimated for geological formations: Dhekiajuli, Girujan, Tipam, Barail, Kopili, Sylhet, Langpur to the granitic basement in normal and thrust faulted areas of the Upper Assam basin using Eaton's exponent of 1.0. The predicted tectonic strain using uniaxial model varies from −0.0044 to 0.0061. The computed tectonic strain using biaxial poroelastic model ranges from 0.000099 to 0.00077 along NE–SW and from −0.001 to −0.0019 along NW–SE directions for normal faulting regime, respectively. In thrust faulting regime, the tectonic strains are obtained as 0.00092 and 0.00053 along NE–SW and NW–SE directions, respectively. The vertical (S V), maximum (S H) and minimum (S h) horizontal stress gradients range 21.7–23.8, 14.9–23.1 and 12.0–21.4 MPa km−1, respectively. Moreover, we have proposed a multiple linear regression model for evaluation of S h from independent parameters, namely, PP, Poisson's ratio and S V from three wells and dependent parameter as leak-off test (LOT) data. This is further tested with other three wells in the study area. The predicted S h is found to have satisfactory correlation with observed LOT for these wells. [ABSTRACT FROM AUTHOR]

Plate tectonics describes the horizontal motion of rigid lithospheric plates away from midoceanic ridges and parallel to transforms, towards deep-sea trenches, where the oceanic lithosphere is subducted into the mantle. This process is the surface expression of modern-day heat loss from Earth. One of the biggest questions in Geosciences today is "when did plate tectonics begin on Earth" with a wide range of theories based on an equally diverse set of constraints from geology, geochemistry, numerical modeling, or pure speculation. In this contribution, we turn the coin over and ask "when was the last appearance in the geological record for which there is proof that plate tectonics did not operate on the planet as it does today". We apply the laws of uniformitarianism to the rock record to ask how far back in time is the geologic record consistent with presently-operating kinematics of plate motion, before which some other mechanisms of planetary heat loss may have been in operation. Some have suggested that evidence shows that there was no plate tectonics before 800 Ma ago, others sometime before 1.8-2.7 Ga, or before 2.7 Ga. Still others recognize evidence for plate tectonics as early as 3.0 Ga, 3.3-3.5 Ga, the age of the oldest rocks, or in the Hadean before 4.3 Ga. A key undiscussed question is: why is there such a diversity of opinion about the age at which plate tectonics can be shown to not have operated, and what criteria are the different research groups using to define plate tectonics, and to recognize evidence of plate tectonics in very old rocks? Here, we present and evaluate data from the rock record, constrained by relevant geochemical-isotopic data, and conclude that the evidence shows indubitably that plate tectonics has been operating at least since the formation of the oldest rocks, albeit with some differences in processes, compositions, and products in earlier times of higher heat generation and mantle temperature, weaker oceanic lithosphere, hotter subduction zones caused by more slab-melt generation, and under different biological and atmospheric conditions. [ABSTRACT FROM AUTHOR]

Yunnan Province is located on the southeastern margin of Tibet and represents an important marker in understanding the tectonic evolution of Tibetan Plateau. In this study, we calculated teleseismic P-wave receiver functions at 49 permanent broadband seismic stations in Yunnan Province and estimated crustal thickness and the bulk crust ratios of P-wave to S-wave velocities using the H-κ method together with more detailed crustal structural profiles from the common conversion point stacking method. There is a significant transition of Moho interface and lower crustal composition along latitude 26°N in northwestern Yunnan. Decrease of crustal thickness with a concomitant increase of Poisson's ratio occurs at station CUX. An interesting phenomenon is that a step-like Moho fashion is observed at several stations, which might correspond to local thermal activities, such as partial melt/lower crust delamination. Our results show changes in crustal properties appear to be associated with varieties in upper mantle structure and compositions, combined with other previous studies. We propose the controlling factor of the dynamic processes below 26°N is the result of eastern forward subduction of the Indian Plate; the northern part is controlled by the redirected material flow from the SE Tibet. [ABSTRACT FROM AUTHOR]

Models of orogens identify subduction of oceanic crust as the key mechanism leading to continental collision. Such models, based inter alia on thermobarometric and geochronological evidence preserved in high-pressure metamorphic rocks and subduction-related magmatism, have been used to explain the convergence of Europe and Adria in the Cretaceous-Cenozoic and the subsequent Alpine orogen. Here, we review the metamorphic, igneous, and sedimentary record of the past 300 Ma of the Alpine orogen to show that there is no evidence of igneous activity during subduction initiation and prograde high-pressure metamorphism, leading to an ~50 Ma hiatus in magmatism, or "arc gap." The closure of rift basins forming the Piemont-Liguria ocean did not follow a classical Wadati-Benioff-type subduction. Instead, subduction initiation at passive margins allowed for the accretion of the hydrated portion of the subducting plate within an orogenic wedge as subduction of dry subcontinental lithosphere inhibited magmatism during subduction initiation and ocean closure. [ABSTRACT FROM AUTHOR]

The upper crust in the SE Tibetan Plateau is rotating around the eastern Himalayan syntax clockwise, and the western margin of the Yangtze Craton has been involved in the active tectonics. However, it is still unclear whether and how the deep crust and upper mantle respond to the plateau expansion. In this study we present a high‐resolution three‐dimensional model of P wave velocity tomography and azimuthal anisotropy in the crust and uppermost mantle beneath the SE Tibetan Plateau determined using traveltime data recorded by a dense seismic network. Widespread low‐velocity zones are revealed around a high‐velocity body in the deep crust and uppermost mantle beneath the southwest Yangtze Craton, where fast‐velocity directions of the azimuthal anisotropy are mostly parallel to the contour lines of the surface topography and the Moho depth along the plateau margin. These results indicate that gravitational potential plays an important role in the crustal and uppermost‐mantle deformations in the SE Tibetan Plateau. Meanwhile, the shallow crust may drop down to the deep crust and drive the ductile deep‐crustal material to intrude into the adjacent regions. The extruded crust is trapped in a deep‐crustal corner and obstructed by the surrounding strong blocks. The trapped crustal material may rise up, causing significant uplift and high heat flow at the surface. Key Points: We present a high‐resolution P wave anisotropic tomography of the SE Tibetan PlateauWidespread low‐velocity zones with margin‐parallel anisotropy exist in the deep crust and uppermost mantleA shallow‐crustal block drops down, causing deep‐crustal and uppermost‐mantle materials to extrude into adjacent regions [ABSTRACT FROM AUTHOR]

Both laboratory experiments and seismic observations indicate that the solid Earth is composed of strongly anisotropic materials and its dynamics can be better constrained by exploring seismic anisotropy. Due to the limited number and poor depth resolution of currently available seismic anisotropy measurements, tectonic regimes of upper mantle deformations beneath Southern California still remain enigmatic and controversial. Here we present high‐resolution three‐dimensional models of P wave azimuthal and radial anisotropy in the crust and upper mantle beneath Southern California obtained by a joint inversion of local‐seismic and teleseismic P wave data. Our results reveal significant depth‐dependent anisotropy in which fast orientations in the lithospheric mantle closely follow the strike of the San Andreas fault and those in the asthenosphere are characterized as a predominantly circular pattern centered in the robust high‐velocity Isabella anomaly beneath the Great Valley. The Isabella anomaly is possibly a remnant of the fossil Farallon slab and is currently experiencing a tectonic regime of lithospheric downwelling, contributing to the development of a circular asthenospheric flow. High‐velocity anomalies are revealed below 300‐km depth beneath areas surrounding the Great Valley, which may reflect the delaminated lithospheric segments. Different rifting processes may take place beneath the Inner Borderland and the Salton Trough whose developments are possibly related to regional mantle upwelling and lithospheric stretching, respectively. Key Points: Depth‐varying azimuthal and radial anisotropies are revealed in the crust and upper mantle beneath Southern CaliforniaPossible circular asthenospheric flow is centered in the Isabella anomaly and lithospheric delamination in its surrounding areasDecompression melting is induced by lithospheric stretching beneath the Salton Trough [ABSTRACT FROM AUTHOR]

Magmatic-textured zircon from medium- to high-K calc-alkaline Warraweena Volcanics (WV) in two drill holes have yielded concordant U-Pb dates of 417 ± 3.5 and 414 ± 4.0 Ma and are interpreted as maximum emplacement ages. The Warraweena volcanics were previously considered to be either Neoproterozoic or Macquarie arc equivalents. Whole-rock εNdt values of these volcanics are +4.5 and +4.8. Along strike of the drill holes, Devonian zircon U-Pb ages (411 ± 5.5 Ma) were obtained from coherent S-type rhyolite flows that have highly negative εNdt values (-7.9 and -7.8). These are a component of the Oxley volcanics. The ages of the Warraweena and Oxley volcanics are identical within uncertainty. The Oxley volcanics (OV) are interbedded with predominantly fine- to medium-grained metasedimentary and so imply a Lower Devonian deposition age for these host rocks. Based on their geophysical characteristics, the metasediments are widely distributed. These metasedimentary rocks yield a wide range of maximum depositional ages, from Early Devonian to earliest Ordovician-latest Cambrian, similar to the Cobar Basin. The absence of complex fabric development typical of Ordovician supracrustal rocks in the region, and conformity with the OV where observable suggest the widespread sedimentation was synchronous with rift-related volcanism in the Early Devonian. Regionally, the WV is temporally, geochemically and isotopically (εNd values) similar to the calc-alkaline Louth Volcanics located over 100 km to the southwest of the WV. Louth Volcanics define a complexly folded belt in geophysical data. Other potentially correlative Early Devonian igneous rocks occur in the nearby Cobar Superbasin and elsewhere in the eastern Lachlan Orogen and are considered to represent the products of a post-orogenic, nascent continental back-arc rift system. [ABSTRACT FROM AUTHOR]

The Late Mesozoic to Cenozoic evolution of Northeast Asia involves successive subduction of the Pacific oceanic crust and amalgamation of the Eurasia, North American, and Okhotsk Sea Plates. The timing of plate collision is essential for understanding the tectonic evolution of Northeast Asia. In this study, we focus on the Okhotsk Sea Plate collision with the Eurasia Plate along the Sakhalin Island, Russian Far East, which is a highly controversial problem, especially about the timing of collision. In order to determine exact timing for this collision, we report zircon U‐Pb data from both the East Sakhalin accretionary complex and postcollisional granitic plutons in the Sakhalin Island. Detrital zircon data from four metasedimentary rocks show that the Sikhote‐Alin orogenic belt is the main provenance for the East Sakhalin accretionary complex. Meanwhile, the youngest detrital zircon age constrains the maximum depositional age of East Sakhalin accretionary complex later than 49 Ma. Both Langeri and Val'za plutons are made of peraluminous S‐type granite. Four granitic samples yielded consistent ages at 36–38 Ma, indicating that both plutons were emplaced at the middle Eocene. Their generation is considered to have been derived through crustal anatexis of accretionary wedge in the lower crust shortly after tectonic thickening caused by the Okhotsk Sea Plate collision with the Eurasia Plate. Consequently, our age data constrain that the Okhotsk Sea Plate and Eurasia Plate collision occurred in the middle Eocene between 49 and 38 Ma. This age range is consistent with late Eocene uncomformity identified in the Sakhalin Island and Okhotsk Sea. Key Points: Detrital zircon ages constrain the maximum depositional age of East Sakhalin accretionary complex at 49 MaLangeri and Val'za S‐type granitic plutons were emplaced at 36–38 MaThe Okhotsk Sea Plate and Eurasia Plate collision occurred in the middle Eocene between 49 and 38 Ma [ABSTRACT FROM AUTHOR]

The eastern sector of the Trans‐Mexican Volcanic Belt (TMVB) is an enigmatic narrow zone that lies just above where the Cocos plate displays a sharp transition in dipping angle in central Mexico. Current plate models indicate that the transition from flat to steeper subduction is continuous through this region, but the abrupt end of the TMVB suggests that the difference in subduction styles is more likely to be accommodated by a slab tear. Based on a high‐resolution shear wave velocity and radial anisotropy model of the region, we argue that a slab tear within South Cocos can explain the abrupt end of the TMVB. We also quantify the azimuthal anisotropy beneath each seismic station and present a well‐defined flow pattern that shows how mantle material is being displaced from beneath the slab to the mantle wedge through the tear in the subducted Cocos plate. We suggest that the toroidal mantle flow formed around the slab edges is responsible for the existence of the volcanic gap in central Mexico. Moreover, we propose that the temperature increase caused by the influx of hot, less dense mantle material flowing through the tear to the Veracruz area may have significant implications for the thermomechanical state of the subducted slab and explain why the intermediate‐depth seismicity ends suddenly at the southern boundary of the Veracruz basin. The composite mantle flow formed by the movement of mantle material through the slab tears in western and southern Mexico may be allowing the Cocos plate to roll back in segments. Plain Language Summary: The Trans‐Mexican Volcanic Belt (TMVB) is a prominent and enigmatic feature of the subduction system in Mexico. Its volcanic style diversity and oblique orientation to the trench are explained by the large along‐strike variations in the subduction parameters of the Rivera and Cocos plates. However, the abrupt termination of the TMVB on its eastern end with the Pico de Orizaba volcano is puzzling as the current slab model suggests that the transition of the Cocos flat‐slab geometry to normal subduction is smooth through this region. There is evidence that suggests that a tear in the slab might be developing, but it is unclear how this feature can support the unusually large topographic gradient that connects the volcanic high peaks with the Veracruz basin just south of the volcanic front. To provide further insight into the transition anatomy of this portion of the subducted slab and its relation with surface topography, we present a detailed and unified model of the velocity structure of the crust and uppermost mantle of central Mexico. Key Points: Evidence from seismic anisotropy suggests the existence of a tear in S Cocos slabThe rollback process of the slab is a key element for the abrupt end of the TMVBThe slab window may create a corner flow for the isolated volcanoes in S Mexico [ABSTRACT FROM AUTHOR]

The South Tianshan Orogen marks the final assembly of the southwestern Central Asian Orogenic Belt (CAOB) and the Karakum–Tarim cratons. Here we present an integrated mineralogical, geochemical, and geochronological study of the Wuwamen ophiolitic mélange in the South Tianshan to better understand the tectonic evolution of the western CAOB and its links to Gondwana and Pangea. Mantle peridotites with mineral compositions similar to those of abyssal peridotites and basalts with N‐MORB geochemical affinities suggest that the Wuwamen ophiolite was formed in a mid‐ocean ridge setting. Arc‐related gabbro and plagiogranite stocks intruding the mantle peridotites yielded zircon U–Pb ages of 441.1 ± 4.2 and 442.8 ± 2.4 Ma, indicating that the Wuwamen ophiolite got emplaced prior to ~440 Ma. Sericite‐quartz schist from the ophiolitic mélange matrix with abundant 481–319 Ma detrital zircon grains is crosscut by a two‐mica granite dike with a zircon U–Pb age of 321.3 ± 1.7 Ma, thereby constraining the formation of the Wuwamen ophiolitic mélange at ~320 Ma. In conjunction with published data, we propose that the South Tianshan Ocean opened in the late Neoproterozoic and promoted the subsequent separation of microcontinents in the western CAOB from the northeast Gondwana margin during Gondwana assembly. Furthermore, the closure of the South Tianshan Ocean led to the final assembly of the southwestern CAOB and the Karakum–Tarim cratons and their incorporation into Pangea at ~320 Ma. Key Points: The Wuwamen ophiolite formed in a mid‐ocean ridge setting and got emplaced prior to ~440 MaThe formation of the Wuwamen ophiolitic mélange suggests that the final closure of the South Tianshan Ocean occurred at ~320 MaThe western Central Asian Orogenic Belt was not accreted to Gondwana prior to collision with Karakum–Tarim as part of Pangea at ~320 Ma [ABSTRACT FROM AUTHOR]

Key Points: Early Cretaceous ophiolite, seamount, or oceanic plateau are vaguely defined, and their crystallization ages are poorly constrainedLatest marine deposits across the suture zone are quite younger than the initial collision ageArc‐related magmatic rocks do not necessarily form in a continental arc; paleomagnetic constraints are mutually conflicting [ABSTRACT FROM AUTHOR]

Abstract: Determining high‐resolution three‐dimensional (3‐D) crustal structures of the Qinling Orogenic Belt (QOB) can reveal significant evidences to enhance our understanding of its tectonic evolution. By jointly inverting group and phase velocity dispersion curves, we obtain a high‐resolution 3‐D shear wave velocity model for the QOB. According to the obviously layered features, which include an E‐W trending high‐velocity structure in the upper crust (0–10 km), a transitional zone in the middle crust (10–30 km), and an approximately N‐S trending low‐velocity zone in the middle‐lower crust (20–40 km), we elucidate the crustal structure as a flyover model to explain how the crust beneath the QOB was deformed under the perpendicular force systems from the NE‐SW and E‐W directions during the Meso‐Cenozoic. First, the apparent NE‐SW trending low‐velocity zone in the middle‐lower crust indicates that the low‐viscosity crustal materials beneath the northeastern Tibetan Plateau did not flow eastward into the eastern Qinling terrane during the Cenozoic. Second, the extension in the northern Qinling Mountains and Weihe Basin was not largely affected by the lateral crustal growth of the NE Tibetan Plateau, which might be the result of deep mantle upwelling and/or residual effects from the subduction of the western Pacific plate. Third, during the Mesozoic, the high‐velocity structures beneath the Hannan‐Micang and Shennongjia‐Huangling domes served as anchors resisting the northward subduction, rotation, and continuous collision of the Yangtze Block. The eastward extruding Hannan‐Micang dome served as an indenter that eventually shaped the present‐day asymmetric style of the Dabashan Orocline during the Cenozoic. [ABSTRACT FROM AUTHOR]

The Bathurst Island archipelago in the central part of the Canadian Arctic Islands, includes Bathurst Island proper and six other significant islands to north and west. This is the site of two intersecting fold belts: the northerly-trending Cornwallis Fold Belt and the westerly-trending Parry Islands Fold Belt Significant components of the report area include Precambrian seismic basement, the Franklinian shelf (Cambrian to Devonian), a Middle and Upper Devonian clastic wedge, and outliers of the Sverdrup Basin (Carboniferous-Cretaceous). Total thickness of the Cambrian to Devonian succession is 7.6–8.8 km in the island group. Oldest identified strata are evaporites of the Middle Ordovician Bay Fiord Formation. These form a ductile decollement zone that at a depth of 4100–5500 m everywhere underlies thrust-folds. Above this are shelf carbonates, deep water mudrocks, and shallow to deep water strata associated with tectonic activity through the upper Silurian to Lower Devonian Cornwallis Fold Belt. The end of uplift-related deposition is marked by a transition to basin fill mudrocks, succeeded in the later Devonian by shelf-deltaic and fluvial sandstones and other clastic rocks. Structures of Cornwallis Fold Belt feature north and in part west-striking thrust panels and evidence of unroofing in early Ludlow to mid-Emsian time. Also included are westerly-transported thrusts kinematically linked to easterly- striking wrench faults that are presumably reactivated as thrusts and forming large interference structures during development of Parry Islands Fold Belt deformation in the Late Devonian to early Carboniferous. Parry Islands Fold Belt features upright surface folds, subsurface thrusts, ductile deformation and detachment in Ordovician salt and Devonian shale. Structures include northerly- and southerly-transported thrusts, zig-zag structures, pop-up and pop-down structures. [ABSTRACT FROM AUTHOR]

Situated between the South Tianshan suture zone to the west and the Solonker suture zone to the east, the Yagan and Zhusileng-Hangwula arcs (YZHAs) in western Inner Mongolia in China occupy a critical place to investigate the tectonic history of the middle segment of the southern Central Asian Orogenic Belt (CAOB). In this work, field-based petrological studies and zircon U-Pb dating results reveal several episodes of granitic magmatism from 400 to 230 Ma in the YZHAs. Whole-rock geochemical and zircon Lu-Hf isotopic data indicate that all the 400-230 Ma granitoids underwent intensive fractional crystallization and were generated by magma mixing involving different proportions of mantle- and crust-derived materials. The ∼400 Ma monzogranites show (high-K) calc-alkaline affinities, akin to S-type granitoids. They were most likely generated in a postcollisional setting, corresponding to the assembly of the YZHAs before the Early Devonian. The 298-290 Ma granitoids belong to transitional I/S-type to A-type, whereas the 280-277 Ma granitoids are typical I-type. These Permian granitoids show increasingly evolved zircon εHf(t) values and formed from crust-mantle magma mixing, suggesting an advancing subduction setting. The ∼230 Ma monzogranites exhibiting fairly positive zircon εHf(t) values (+6.26 to +10.49) and high contents of mafic compositions and transition elements probably formed in a postcollisional setting after the assembly of the YZHAs and the Alxa Terrane. We infer that the final assembly of the middle segment of the southern CAOB probably occurred in the Early-Middle Permian. [ABSTRACT FROM AUTHOR]

Northwest Zhejiang Province (NWZJ) is located in the southeastern Lower Yangtze River Belt, southeastern China. Here we document the occurrence of both magnesian (149-131 Ma) and ferroan (162-121 Ma) granitoids in NWZJ. The magnesian granitoids are calc-alkalic peraluminous in composition, with a wide range of SiO2 (58-72 wt%) contents. They have high K2O/Na2O, Sr/Y, and (La/Yb)N ratios, with insignificant Eu anomalies, whereas the calc-alkalic peraluminous ferroan granites have high SiO2 (76-77 wt%) contents, Fe indices (FeO*/(FeO*+MgO)), and Ga/Al ratios. The ferroan granites also have low Ce/Pb and Nb/U ratios, with strong Ba, Sr, and Eu negative anomalies. Most of the rocks have similar zircon Lu-Hf isotopes (εHf(t)=−6.0 to −0.7). However, rocks from two ferroan granitic bodies (Huangshitan and Jiuligang) have more depleted Hf isotopes, with εHf(t) ranging from −1.9 to 5.9. The whole-rock Nd isotopes of the ferroan granites (εNd(t)=−6.5 to −3.2) are slightly more depleted than those of magnesian granitoids (εNd(t)=−8.8 to −5.1). In addition, all ferroan granites show similar and high present-day whole-rock Pb isotopic ratios (18.3-18.8 for 206Pb/204Pb, 15.6-15.7 for 207Pb/204Pb, and 38.5-39.0 for 208Pb/204Pb). On the basis of published data and our new results, we propose that the magnesian granitoids were generated by partial melting of lower-crustal materials, whereas the ferroan granites were derived from a similar source but some more-depleted materials were added into their source after ∼135 Ma. The water contents of the magma may have played an important role in determining the different geochemical affinities of the felsic magmatism. The felsic magmatism occurred under an extensional setting during the period 162-121 Ma. The extension of the lithosphere was further enhanced and followed by upwelling of asthenospheric mantle after ∼135 Ma. This study suggests that a change in the tectonic regime occurred at ∼135 Ma in NWZJ, which may have been triggered by the rollback of the subducted Paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

The Juchatengo complex (JC) suite is located between the Proterozoic Oaxacan complex to the north and the Xolapa complex to the south, and was amalgamated by late Paleozoic magmatism. It consists of mafic and sedimentary rocks that have oceanic affinities, with internal pseudostratigraphic, structural and metamorphic characteristics, which resemble a typical upper-level ophiolite assemblage. New U-Pb zircon and previous hornblende K-Ar analyses yield ages of ca. 291-313 Ma (U-Pb) for plagiogranites and ca. 282-277 Ma for tonalites intruding the entire sequence, including pelagic sediments at the top, with a maximum deposition age of ca. 278 Ma and noteworthy local provenance. These data constrain the age of the JC to the Late Pennsylvanian-Early Permian period. Hf isotopic analyses obtained from zircons in the JC plagiogranite and tonalite show that they come from a similar primitive mantle source (176Hf/177Hf: 0.282539-0.283091; ƐHf(t): + 3.2 to + 15.0). ƐHf(t) values from near 0 to − 2.8 in the tonalites indicate a contribution from the continental crust. Trace elements and REE patterns in whole rock and zircons point to a primitive mantle source for differentiated mafic, plagiogranite dykes and tonalitic plutons. Geochronological and geochemical data address the generation of new oceanic crust above the subduction zone, probably in a backarc setting. In this tectonic scenario, the JC ophiolite originated due to the convergence of the paleo-Pacific plate below the already integrated Oaxacan and Acatlán complexes in western Pangea. The dextral displacement places the deformation in a transtensional regime during the late Paleozoic age. [ABSTRACT FROM AUTHOR]

The ages and origins of metasedimentary rocks, which were previously mapped as Precambrian, are critical in rebuilding the orogenic process and better understanding the Phanerozoic continental growth in the Central Asian Orogenic Belt (CAOB). The Beishan Complex was widely distributed in the southern Beishan Orogenic Collage, southernmost CAOB, and their ages and tectonic affinities are still in controversy. The Beishan Complex was previously proposed as fragments drifted from the Tarim Craton, Neoproterozoic Block or Phanerozoic accretionary complex. In this study, we employ detrital zircon age spectra to constrain ages and provenances of metasedimentary sequences of the Beishan Complex in the Chuanshanxun area. The metasedimentary rocks here are dominated by zircons with Paleoproterozoic–Mesoproterozoic age (~1160–2070 Ma), and yield two peak ages at 1454 and 1760 Ma. One sample yielded a middle Permian peak age (269 Ma), which suggests that the metasedimentary sequences were deposited in the late Paleozoic. The granitoid and dioritic dykes, intruding into the metasedimentary sequences, exhibit zircon U–Pb ages of 268 and 261 Ma, respectively, which constrain the minimum deposit age of the metasedimentary sequences. Zircon U–Pb ages of amphibolite (274 and 216 Ma) indicate that they might be affected by multi-stage metamorphic events. The Beishan Complex was not a fragment drifted from the Tarim Block or Dunhuang Block, and none of cratons or blocks surrounding Beishan Orogenic Collage was the sole material source of the Beishan Complex due to obviously different age spectra. Instead, 1.4 Ga marginal accretionary zones of the Columbia supercontinent might have existed in the southern CAOB, and may provide the main source materials for the sedimentary sequences in the Beishan Complex. [ABSTRACT FROM AUTHOR]

A Mesozoic to Paleogene polyphase tectonic model presented here for the southern United States (U.S.) Cordillera provides new insight into style and timing of Mesozoic--Paleogene deformation and basin formation in the region south of the Colorado Plateau and Mogollon-Datil volcanic field. The model proposes reverse reactivation of Jurassic normal faults during Late Cretaceous Laramide shortening. It also recognizes late Paleogene east-west-- and northwest-southeast--trending normal faults formed during a north-south extensional event that postdated Laramide shortening and preceded Neogene Basin and Range extension. Late Jurassic to Early Cretaceous extension generated northwest-southeast normal faults that formed part of the Border rift system that extended from southern California to the northwestern Gulf of Mexico. The normal faults cut Mesoproterozoic basement rocks, and localized subsequent uplift of basement rocks during Late Cretaceous fault reactivation that formed northwest- southeast--trending Laramide uplifts of southwest New Mexico and southeastern Arizona. The Hidalgo uplift, reconstructed here from structural relations in the Little Hatchet and Big Hatchet Mountains of southwestern New Mexico, is bound by bivergent reverse faults that resulted from tectonic inversion of a Jurassic--Early Cretaceous graben. The Hidalgo uplift is flanked to the north by the Campanian to earliest Maastrichtian Ringbone basin, which accumulated synorogenic continental strata and basaltic andesite flows from ca. 75 to 70 Ma. The Ringbone basin was converted from a subsiding basin in the Little Hatchet Mountains to a volcanic center by ca. 69 Ma, the emplacement age of an assemblage of shallow, subvolcanic intrusions termed the Sylvanite plutonic complex. The basement-involved structural style and yoked intermontane basin resemble other Laramide uplifts and basins in the Rocky Mountain Cordillera and refute alternative Laramide models of strikeslip faulting or regionally extensive horizontal thrust faults in southwestern New Mexico, the latter of which fail to account for basement-cored uplifts. A significant difference with the Rocky Mountain Laramide province is the size of the uplifts and basins and the close association of southern U.S. Cordilleran structures to nearby Late Cretaceous magmatic centers, which contributed to interstratified volcanic and volcaniclastic rocks in the basin fill. Upper Eocene--Oligocene ignimbrites and volcaniclastic rocks of the Boot Heel volcanic field of southwestern New Mexico unconformably overlie Laramide syntectonic strata and bury eroded Laramide structures. The distribution of the Paleogene volcanic rocks in the Little Hatchet and Big Hatchet Mountains is in part controlled by synmagmatic east-west and northwest-southeast normal faults active from ca. 34 to 27 Ma, the age range of rhyolite dikes intruded along the faults. Two generations of intrusive rocks occupy these normal faults in the Little Hatchet Mountains: (1) older (ca. 34 Ma) phaneritic stocks and dikes in the central and southern parts of the range, and (2) younger (31--27 Ma) aphanitic latite and rhyolite dikes. East-west--trending faults and dikes are cut by north-south faults formed during Basin and Range extension. The late Eocene--early Oligocene north-south extension provides an important minimum age limit for Laramide shortening, which ended prior to ca. 34 Ma. [ABSTRACT FROM AUTHOR]

We used the World Gravity Map (WGM 2012) data to investigate the Archean Congo craton and the Oubanguides orogenic belt in Cameroon. The Oubanguides orogenic belt constitutes, from northwest to southeast, the Neoproterozoic West Cameroon domain, the Paleoproterozoic-Neoproterozoic Adamawa-Yade domain, and the dominantly Neoproterozoic Yaoundé domain (the crustal expression of the suture zone between the Congo craton and the orogenic terranes). We analyzed the WGM 2012 data to identify different gravity anomalies. We also applied the two-dimensional (2D) radially-averaged power spectral analysis to the WGM 2012 data to estimate the Moho depth. Additionally, we developed a 2D forward gravity model along a N S profile to image the lithospheric structure of the Precambrian entities. We found that: (1) the Congo craton, the Yaoundé domain, the southeastern part of the West Cameroon domain, and the northern part of the Adamawa-Yade domain are characterized by low gravity anomaly. (2) the southern part of the Adamawa-Yade domain is marked by a pronounced E-W trending high gravity anomaly. (3) the crust is thicker beneath the Congo craton, the Yaoundé domain and the southern part of the Adamawa-Yade domain. (4) the presence of a denser lower crust material beneath the southern part of the Adamawa-Yade domain. We propose that this denser crustal material is an under-thrusted portion of the Congo craton that has been densified through metacratonization processes that accompanied collision between the craton and the orogenic terranes. This is in good agreement with geological and geochemical observations indicating that the northern edge of the Congo craton and the Adamawa-Yade domain had undergone metacratonization during the Neoproterozoic. Our suggestion is also in good agreement with observations which show that the margins of many cratons worldwide have been decratonized due to subduction processes. Our work highlights the importance of potential field geophysical data in mapping the metacratonized margins of cratons. [ABSTRACT FROM AUTHOR]

Rheological heterogeneities in the lithosphere have first order control on the topographical expression of tectonic processes. Pre-existing orogenic suture zones localise extensional deformation resulting in asymmetric basins. Such crustal geometries are often in contrast with the more symmetric regional lithospheric structure observed beneath extensional basins. We study such (a)symmetries and their controlling parameters by conducting a series of 2D thermo-mechanical numerical experiments of the extension of an overthickened, hot lithosphere that contains a weakness zone. The modelling shows that syn-rift subsidence is low to moderate creating asymmetric half grabens where extension migrates in space and time, grouped in an overall symmetrical appearance on a larger scale. The initial lithospheric mantle asymmetry is attenuated by the lateral heat conduction and further dynamic evolution of the thermal anomaly during the “post-rift” phase, resulting in differential vertical movements of the crust including additional 2–3 km subsidence in the basin centre. The modelling shows that the initial crustal and lithospheric thicknesses, rate of extension and surface processes strongly control the thermo-mechanical evolution of the extensional system. The numerical modelling yields new insights into the mechanics of coupling between near-surface kinematics and the evolution of deep lithospheric structure in the Pannonian basin and the Aegean, two of Europe's largest back-arc systems. [ABSTRACT FROM AUTHOR]

The basaltic pillow lavas in the Liuyuan region of NW China, considered to be part of an ophiolitic suite, have been central to the models on tectonic setting, evolution and timing of the final closure of the Palaeo-Asian Ocean. New field evidence on the sedimentary units associated with the basalts reveals comparable sequences in the northern and southern flanks of the Liuyuan Volcanic Belt with coarse to fine sediments from periphery to the centre. The dacites and rhyolites formed coevally with the pillow basalts. The pillow basalts are interlayered with lacustrine sandstone, claystone and clayey lake deposits. Detrital zircons from these sediments yield zircon U–Pb ages of 291–285 Ma. Andesites, dacites and rhyolites from the basaltic sequence yield U–Pb ages of 280–277 Ma, similar to the 282–280 Ma ages of gabbros that intrude the pillow lavas. All these rocks cover the 460–440 Ma granite and greenschist basement and have been intruded by gabbros of c. 272 Ma age, with subsequent (230–227 Ma) north–south contractional thrusting and folding. The data from our study are incompatible with the existing models that consider the basalts as part of an ophiolitic suite. Along the northern continental margin of China from west to east, the Tarim, Dunhuang-Alxa and North China cratonic areas all show evidence for regional extension through rifting during early–middle Permian time. These rift features and basaltic eruptions occurred coevally with the assembly of various microcontinental blocks against the Siberian craton at c. 300–250 Ma, synchronous with amalgamation of the Central Asian Orogenic Belt (CAOB) on the northern side of the Liuyuan Rift. These events were also broadly synchronous with formation of the global supercontinent Pangea. [ABSTRACT FROM PUBLISHER]

The curvilinear ~ E-W structures of the southern Thomson Orogen are approximately orthogonal to the general ~ N-S structural trend of the Tasmanides of eastern Australia. The origin of these orogen-perpendicular structures and their implications to tectonic reconstructions of eastern Gondwana are not fully understood. Here we use geophysical data to unravel the geometry, kinematics and possible timing of major structures along the boundary between the Thomson Orogen and the southern Tasmanides (Delamerian and Lachlan orogens). Aeromagnetic data from the southern Thomson Orogen show WNW, E-W and/or ENE trending structural grains, corresponding to relatively long wavelength linear geophysical anomalies. Kinematic analyses indicate strike-slip and transpressional deformation along these geophysically defined faults. Structural relationships indicate that faulting took place during the Benambran (Late Ordovician to Middle Silurian) and Tabberabberan (late Early to Middle Devonian) orogenies. However, some of the described crustal-scale structures may have developed in the Cambrian during the Delamerian Orogeny. Interpretation of deep seismic data shows that the crust of the southern Thomson Orogen is substantially thicker than the Lachlan Orogen crust, which is separated from the Thomson Orogen by the north-dipping Olepoloko Fault. A major lithospheric-scale change across this boundary is also indicated by a contrast in seismic velocities. Together with evidence for the occurrence of Delamerian deformation in both the Koonenberry Belt and northeastern Thomson Orogen, and a significant contrast in the width of the northern Tasmanides versus the southern Tasmanides, it appears that the southern Thomson Orogen may represent the locus of orogen-perpendicular segmentation, which may have occurred in response to along-strike plate boundary variations. [ABSTRACT FROM AUTHOR]

Knowledge of the crustal structure is important for understanding the tectonic framework and geological evolution of southeastern China and adjacent areas. In this study, we integrated the datasets from the TAIGER (TAiwan Integrated GEodynamic Research) and ATSEE (Across Taiwan Strait Explosion Experiment) projects to resolve onshore-offshore deep crustal seismic profiles from the Wuyi-Yunkai orogen to the Taiwan orogen in southeastern China. Three seismic profiles were resolved, and the longest profile was 850 km. Unlike 2D and 3D first arrival travel-time tomography from previous studies, we used both refracted and reflected phases (Pg, Pn, PcP, and PmP) to model the crustal structures and the crustal reflectors. In total, data from 40 shots, 2 earthquakes, and approximately 1,950 stations were used; 15,612 arrivals were selected among three transects. Using these data, we determined the complex crustal evolution since the Paleozoic era , involving the closed Paleozoic rift basin in central Fujian, the Cenozoic extension due to the South China Sea opening beneath the coastline of southern Fujian, and the on-going collision of the Taiwan orogen. The shape of the Moho, which also reflects the crustal evolution, can be summarized as follows: ~ 30 km deep to the west of Fujian, deepening toward central Fujian (~ 35 km), becoming shallower toward the Taiwan Strait (~ 28 km), deepening again toward the mountain belt of Taiwan (~ 42 km), and becoming shallower toward the Pacific Ocean (~ 10 km). [ABSTRACT FROM AUTHOR]

Defining the structural style of fold–thrust belts and understanding the controlling factors are necessary steps towards prediction of their long-term and short-term dynamics, including seismic hazard, and to assess their potential in terms of hydrocarbon exploration. While the thin-skinned structural style has long been a fashionable view for outer parts of orogens worldwide, a wealth of new geological and geophysical studies has pointed out that a description in terms of thick-skinned deformation is, in many cases, more appropriate. This paper aims at providing a review of what we know about basement-involved shortening in foreland fold–thrust belts on the basis of the examination of selected Cenozoic orogens. After describing how structural interpretations of fold–thrust belts have evolved through time, this paper addresses how and the extent to which basement tectonics influence their geometry and their kinematics, and emphasizes the key control exerted by lithosphere rheology, including structural and thermal inheritance, and local/regional boundary conditions on the occurrence of thick-skinned tectonics in the outer parts of orogens. [ABSTRACT FROM PUBLISHER]

The idea that climatically modulated erosion may impact orogenic processes has challenged geoscientists for decades. Although modeling studies and physical calculations have provided a solid theoretical basis supporting this interaction, to date, field-based work has produced inconclusive results. The central–western Alborz Mountains in the northern sectors of the Arabia–Eurasia collision zone constitute a promising area to explore these potential feedbacks. This region is characterized by asymmetric precipitation superimposed on an orogen with a history of spatiotemporal changes in exhumation rates, deformation patterns, and prolonged, km-scale base-level changes. Our analysis suggests that despite the existence of a strong climatic gradient at least since 17.5 Ma, the early orogenic evolution (from ∼36 to 9–6 Ma) was characterized by decoupled orographic precipitation and tectonics. In particular, faster exhumation and sedimentation along the more arid southern orogenic flank point to a north-directed accretionary flux and underthrusting of Central Iran. Conversely, from ∼6 to 3 Ma, erosion rates along the northern orogenic flank became higher than those in the south, where they dropped to minimum values. This change occurred during a ∼3-Myr-long, km-scale base-level lowering event in the Caspian Sea. We speculate that mass redistribution processes along the northern flank of the Alborz and presumably across all mountain belts adjacent to the South Caspian Basin and more stable areas of the Eurasian plate increased the sediment load in the basin and ultimately led to the underthrusting of the Caspian Basin beneath the Alborz Mountains. This underthrusting in turn triggered a new phase of northward orogenic expansion, transformed the wetter northern flank into a new pro-wedge, and led to the establishment of apparent steady-state conditions along the northern orogenic flank (i.e., rock uplift equal to erosion rates). Conversely, the southern mountain front became the retro-wedge and experienced limited tectonic activity. These observations overall raise the possibility that mass-distribution processes during a pronounced erosion phase driven by base-level changes may have contributed to the inferred regional plate-tectonic reorganization of the northern Arabia–Eurasia collision during the last ∼5 Ma. [ABSTRACT FROM AUTHOR]

Understanding details of accretionary complex architecture is essential to understanding construction of oceanic "outer" sides of orogens. The architecture of the Franciscan Complex (California), considered by many to be the "type" accretionary complex, is widely viewed in the context of terranes or belts delimited by reconnaissance mapping that reveals neither regional variations within terranes nor critical details of stratigraphy and structure. The architectural importance of Franciscan mélanges is recognized, but the importance of sandstone-matrix mélanges and olistostromal sandstones is not. Large-scale mapping in Sonoma and Marin counties, California, shows that Franciscan rocks are deformed, submarine-fan units of Facies A-E, plus Facies F olistolith-bearing submarine channel sandstones and olistostromal sandstone- and shale-matrix mélanges. Some mélanges are polygenetic with a sedimentary origin and a tectonic overprint. Glaucophane schists were recycled into conglomerates and olistostromes. Mappable units constitute members, broken and dismembered formations, and mélanges. Considering the stratigraphy and structure evident at the 1:24,000 scale, accretion via a subduction channel mechanism is impossible. The Sonoma-Marin Central belt or Central terrane (mélange) is not a monolithic shale-matrix mélange and lacks this characteristic of rocks assigned the same name to the north. Franciscan rocks here structurally underlie thrust-faulted fragments of a regional ultramafic sheet and, locally, an underlying exotic block-bearing serpentinite-matrix mélange. The detailed mapping shows that regional relations among and within Franciscan terranes and belts are poorly understood and suggests that such mapping is needed to clarify accretionary complex architecture and history. The implication for accretionary complex studies, in general, is that, while terrane or belt designations provide a general picture of the collage nature of accretionary complexes and clarification of regional relationships, only large-scale structural and stratigraphic studies can elucidate the architectural details of these orogenic complexes. [ABSTRACT FROM AUTHOR]

N S shortening in front of the Adriatic indenter, surface uplift and exhumation of the Tauern window area characterize the Late Oligocene to recent tectonic evolution of central sectors of the Eastern Alps. The resulting structures are typified by eastward tilted blocks, separated by extensional corridors. The eastward retreat of the subduction zone in front of the Carpathians induced strong Miocene E--W extension and basement subsidence in the Pannonian basin realm; surface uplift in the Tauern window area created E--W topographic and exhumation gradients, allowing the brittle upper crust to move along the mid-crustal ductile decollément level towards the east. Subject of research is the area between the viscous Penninic zone of the eastern Tauern Window and the overlying brittle Austroalpine basement units with deeply eroded/inverted basins on top. We use published apatite fission track (AFT) and apatite and zircon (U-Th)/He (AHe, ZHe) data from two sections of the Hohe Tauern to the east to constrain the E--W exhumation gradient. A W--E section along the southern Northern Calcareous Alps and sections along the Mur-Mürz fault zones are included for comparison, too. Based on AFT, ZHe and AHe data and assuming a thermal gradient of 30 °C/km, a tilt angle of ca. 4° is found similar for both basement sections. This low gradient is close to a gradient typical for viscous material with low shear strength. These relationships imply that a gravitational collapse alone might be sufficient to explain the eastward motion of the brittle Austroalpine crust over a thick viscous Penninic layer. Flow above a low-friction viscous layer also explains the eastward tilting of blocks, including the Saualpe and Koralpe blocks, along ca. N--S antithetic high-angle dextral transtensional faults. The present-day structure east of the Tauern window within the Eastern Alps could be explained, therefore, by intra-orogenic raft tectonics, which represents the motion of an inclined brittle upper layer on a highly ductile, plastically deformed lower layer. [ABSTRACT FROM AUTHOR]

The Eastern Lesser Himalayan fold-thrust belt is punctuated by a row of orogen-transverse domal tectonic windows. To evaluate their origin, a variety of thrust-stack models have been proposed, assuming that the crustal shortening occurred dominantly by brittle deformations. However, the Rangit Window (RW) in the Darjeeling-Sikkim Himalaya (DSH) shows unequivocal structural imprints of ductile deformations of multiple episodes. Based on new structural maps, coupled with outcrop-scale field observations, we recognize at least four major episodes of folding in the litho-tectonic units of DSH. The last episode has produced regionally orogen-transverse upright folds (F4), the interference of which with the third-generation (F3) orogen-parallel folds has shaped the large-scale structural patterns in DSH. We propose a new genetic model for the RW, invoking the mechanics of superposed buckling in the mechanically stratified litho-tectonic systems. We substantiate this superposed buckling model with results obtained from analogue experiments. The model explains contrasting F3-F4 interferences in the Lesser Himalayan Sequence (LHS). The lower-order (terrain-scale) folds have undergone superposed buckling in Mode 1, producing large-scale domes and basins, whereas the RW occurs as a relatively higher-order dome nested in the first-order Tista Dome. The Gondwana and the Proterozoic rocks within the RW underwent superposed buckling in Modes 3 and 4, leading to Type 2 fold interferences, as evident from their structural patterns. [ABSTRACT FROM AUTHOR]

Abstract: The Solonker suture zone is one of the most important tectonic boundaries in the southeastern part of the Central Asian Orogenic Belt (CAOB). An ~630km-long reflection seismic profile across this suture was recently completed by the Chinese SinoProbe Project. The processed seismic data show clear crustal structures and provide new constraints on the tectonic and crustal evolution models. The Moho is delineated as a relatively flat boundary between a strongly reflective lower crust and a transparent mantle at a depth of ~40–45km (~14.5s two-way travel time), which is in agreement with the refraction data recorded along the same profile. In a broad view, the profile images an orogen that appears bivergent with, and approximately centered on, the Solonker suture zone. The southern portion of this profile is dominated by a crustal-scale, cratonward propagating fold-and-thrust system that formed during the late Permian and Triassic through collision and subsequent convergence in a post-collisional stage. The major thrust faults are truncated by Mesozoic granitoid plutons in the upper crust and by the Moho at the base of the crust. This geometry suggests that the Moho was formed after the thrusting event. The northern portion of the profile, although partially obliterated by post-collisional magmatic bodies, shows major south-dipping folding and thrusting. Bands of layered reflectors immediately overlying the Moho are interpreted as basaltic sills derived from the mantle. Episodic mafic underplating may have occurred in this region, giving rise to post-collisional magmatic events and renewal of the Moho. A few mantle reflectors are also visible. The overall geometry of these mantle reflectors supports the tectonic models that the southern orogen (Manchurides) experienced south-directed subduction and the northern orogen (Altaids) underwent north-directed subduction prior to collision along the Solonker suture zone. [Copyright &y& Elsevier]

Laterally extensive belts of mélange characterize Phanerozoic convergent plate margins, but are rare in Archean terranes. We document a late Archean mélange in the Zanhuang Massif of the North China Craton (NCC). The Zanhuang mélange separates a passive margin to foreland basin sequence developed on the western edge of the Eastern Block of the NCC from an arc terrane consisting of trondhjemitic, tonalitic and granodioritic (TTG) gneisses in the Central Orogenic Belt (COB) of the NCC. The mélange belt contains a structurally complex tectonic mixture of metapelites, metapsammites, marbles and quartzites mixed with exotic tectonic blocks of ultramafic and metagabbroic rocks, metabasalts that locally include relict pillow structures, and TTG gneisses. All units in the mélange have been intruded by mafic dikes that were subsequently deformed, and are now preserved as garnet–amphibolite boudins. We interpret the mélange to mark the suture zone between the Eastern Block and the arc terrane in the COB. Field relationships and geochemistry suggest that the exotic ultramafic–metagabbroic–metabasaltic blocks are possible slivers of an intra-oceanic arc or fore-arc ophiolite incorporated into the mélange during the arc–continent collision process. A circa 2.5Ga granitic pluton intrudes the mélange and undeformed circa 2.5Ga pegmatites cut the mélange. Tectonic models for the evolution of the COB are varied, but include models that favor collision at 2.5Ga, 2.1Ga, and 1.8Ga. This work shows clearly, from field structural relationships and geochronology, that the first collision must have occurred prior to 2.5Ga, consistent with late Archean suturing of the western margin of the Eastern Block with an arc terrane (Fuping terrane) during an arc–continent collision. The presence of an Archean mélange with exotic blocks in a suture zone between an Archean arc and continental margin is clear evidence for the operation of plate tectonics at circa 2.5Ga. [ABSTRACT FROM AUTHOR]

The Paiku composite leucogranitic pluton in the Malashan gneiss dome within the Tethyan Himalaya consists of tourmaline leucogranite, two-mica granite and garnet-bearing leucogranite. Zircon U-Pb dating yields that (1) tourmaline leucogranite formed at 28.2±0.5 Ma and its source rock experienced simultaneous metamorphism and anatexis at 33.6±0.6 Ma; (2) two-mica granite formed at 19.8±0.5 Ma; (3) both types of leucogranite contain inherited zircon grains with an age peak at ∼480 Ma. These leucogranites show distinct geochemistry in major and trace elements as well as in Sr-Nd-Hf isotope compositions. As compared to the two-mica granites, the tourmaline ones have higher initial Sr and zircon Hf isotope compositions, indicating that they were derived from different source rocks combined with different melting reactions. Combined with available literature data, it is suggested that anatexis at ∼35 Ma along the Himalayan orogenic belt might have triggered the initial movement of the Southern Tibetan Detachment System (STDS), and led to the tectonic transition from compressive shortening to extension. Such a tectonic transition could be a dominant factor that initiates large scale decompressional melting of fertile high-grade metapelites along the Himalayan orogenic belt. Crustal anatexis at ∼28 Ma and ∼20 Ma represent large-scale melting reactions associated with the movement of the STDS. [ABSTRACT FROM AUTHOR]

Abstract: The Tongbai orogen is located in a key tectonic position linking the Qinling orogen to the west and the Dabie-Sulu orogen to the east. This orogen comprises a Paleozoic accretionary orogenic system in the north and a Permo–Triassic collisional orogenic system in the south; hence it may serve as an ideal place to unravel the tectonic evolution from the initial oceanic subduction/accretion to the final continental collision between the Sino-Korean and Yangtze cratons. U Pb zircon geochronology of metasedimentary and metaigneous rocks and geochemical characterization of metabasalts indicate a close genetic relationship between the individual tectonic units of the Paleozoic accretionary orogenic system: (1) the Kuanping Group as a Neoproterozoic-Ordovician subduction-accretion complex which received sediments from the Qinling microcontinent, (2) the Erlangping Group and Huanggang diorite-granodiorite complex as an Ordovician–Silurian island arc evolving from backarc basin, (3) the Qinling Group as a Precambrian microcontinent converted into continental arc during the Ordovician, (4) the Guishan Complex as a mixture of the Qinling continental arc and Devonian forearc sediments, and (5) the Nanwan Flysch as a Devonian forearc sequence deposited on the newly accreted active margin of the Sino-Korean craton. Consequently, the northern and southern boundaries of the Paleozoic accretionary orogenic system represent two sutures of the Qinling microcontinent with the Sino-Korean and Yangtze cratons. The new and previously published data reveal that the tectonic evolution of the Tongbai orogen involved a series of events from Ordovician–Early Silurian (ca. 490–440Ma) oceanic subduction and arc magmatism, Silurian–Early Devonian (ca. 440–400Ma) arc-continent collision, Carboniferous (ca. 340–310Ma) oceanic subduction and accretion, Late Permian–Triassic (ca. 260–200Ma) continental subduction and collision, to Cretaceous (ca. 140–90Ma) extension and lateral eastward extrusion. The entire accretionary orogenic processes until the final collision between the Sino-Korean and Yangtze cratons may have lasted more than 200Ma. [Copyright &y& Elsevier]

The article presents abstracts on geological topics which include the Indo-Asian Collision, orogenic evolution in the Andes, and the inner structure of mud volcanoes.

The Lower Cretaceous Fortress Mountain Formation occupies a spatial and temporal niche between syntectonic deposits at the Brooks Range orogenic front and post-tectonic strata in the Colville foreland basin. The formation includes basin-floor fan, marine-slope and fan-delta facies that define a clinoform depositional profile. Texture and composition of clasts in the formation suggest progressive burial of a tectonic wedge-front that included older turbidites and mélange. These new interpretations, based entirely on outcrop study, suggest that the Fortress Mountain Formation spans the boundary between orogenic wedge and foredeep, with proximal strata onlapping the tectonic wedge-front and distal strata downlapping the floor of the foreland basin. Our reconstruction suggests that clinoform amplitude reflects the structural relief generated by tectonic wedge development and load-induced flexural subsidence of the foreland basin. [ABSTRACT FROM AUTHOR]

An orocline is a thrust belt or orogen that is curved in map-view due to it having been bent or buckled about a vertical axis of rotation. Two distinct types of oroclines are recognized: progressive and secondary. Progressive oroclines are restricted to the scale of a thrust sheet to thrust belt, are thin-skinned, and develop during thrust sheet emplacement. Secondary oroclines are larger, occurring at the scale of an orogen, and are plate-scale features that affect crust and lithospheric mantle. Unlike progressive oroclines, which develop during initial orogenesis and in response to the same orogen-perpendicular stress responsible for thrust sheet emplacement, secondary oroclines are extra-orogenic, developing after initial orogenesis and in response to an orogen-parallel principal compressive stress that is oriented at a high angle to the stress responsible for orogen development. We present case studies of the Wyoming Salient, a progressive orocline that characterizes the Sevier thrust belt of the western United States, and the coupled Cantabrian and Central Iberian oroclines, which are linked secondary oroclines affecting the Variscan orogen of Iberia. The vertical-axis rotations involved in progressive and secondary orocline formation are most readily quantified through paleomagnetic analysis. Detailed three-dimensional palinspastic restoration that incorporates translation rotation and strain can distinguish the role, if any, of primary curvature in progressive oroclines. The use of tectonic vectors, such as paleocurrent directions, provides a means of recognizing and characterizing the initial geometry of secondary oroclines. Because secondary oroclines involve the entire lithosphere, detailed studies of coeval metamorphism and magmatism provide a means of constraining the fate of the mantle lithosphere during oroclinal buckling. [ABSTRACT FROM AUTHOR]

Abstract: Understanding the Mesozoic–Cenozoic tectonic evolution of the North China Craton (NCC) and the NE Tibetan Plateau (TP) requires detailed knowledge of the lithospheric structure. Using dense regional networks and temporary deployments as well as updated reference models, we obtain the crust and upper mantle structure to 120km depth. Our tomographic results show several major features, which have particular implications for the Weihe–Shanxi rift system (WSRS), deformation of the NE TP, and lithospheric evolution of the NCC. Beneath the WSRS, the crust gradually thickens from south to north, the lithospheric mantle gradually becomes slower, and the mid-lower crustal velocities are lower in the Weihe Rift, where rifting of the WSRS initiated. We suggest that along-strike variations of the lithospheric structures of the WSRS have played an important role in its multistage evolution. A low-velocity zone (LVZ) in the mid-crust beneath the Qilian Orogen is characterized by relatively higher velocities compared to LVZs in other parts of the TP. Thus, coherent lithospheric deformation may occur due to the high viscosity of the LVZ during early plateau growth, causing strong anisotropy to develop. The western NCC (including the Ordos Block and part of the Alashan Block) shows a high-velocity cratonic root extending to the base of our model. In contrast, the lithosphere of the eastern NCC appears to have been completely modified during the Mesozoic through Cenozoic and presents a thin lithosphere of relatively low velocities underlain by hot asthenosphere. We observed significant upper-mantle heterogeneities in the NCC, which may reflect its diachronous lithospheric modification. [Copyright &y& Elsevier]

The Pacific-Australian tectonic plate boundary through the South Island of New Zealand consists of the transpressional Southern Alps mountain belt and the transcurrent Marlborough Fault System, both of which have active tectonically driven hydrothermal systems, with topographically driven meteoric incursion and warm springs. The Southern Alps hydrothermal system is relatively diffuse, with little or no fault control, and is channelled through scattered extensional sites beneath the mountains, where gold mineralisation is occurring locally. The hydrothermal activity along the Marlborough Fault System is controlled by the principal faults in well-defined valleys separated by narrow high ridges. Lateral evolution of Marlborough fault strands southwestwards into the Southern Alps has caused diversion of diffuse Southern Alps hydrothermal activity into the structural superimposition zone, where fluid flow is increasingly being controlled by faults. This hydrothermal diversion was accompanied by major topographic reorientation and river drainage reversal in the late Quaternary. Vein swarms now exposed in the remnants of the Southern Alps north of the superimposition zone formed at shallow levels, with some evidence for fluid boiling, from a mixture of meteoric and deep-sourced fluid. These veins, some of which contain gold, are part of an abandoned <1 million-year-old hydrothermal zone beneath the fossil topographic divide of the Southern Alps that has now been dismembered by lateral incursion of the Marlborough fault strands. Observations on this active plate boundary provide some insights into processes that controlled orogenic gold mineralisation in ancient belts, particularly with respect to relationships between hydrothermal fluid flow, structure and topography. [ABSTRACT FROM AUTHOR]

The structural data and available geochronological constraints suggest that the Gonzha tectonic block located in the northeastern part of the Argun-Idermeg superterranes, Central Asian orogenic belt, is considered as an analogue of Cordilleran metamorphic core complexes of western Transbaikalia. These metamorphic core complexes, as well as the Gonzha block, may have resulted from collapse of a Late Mesozoic orogen after closure of the Mongolia-Okhotsk paleo-ocean basin. [ABSTRACT FROM AUTHOR]

This paper reviews the Kamchatka seismicity for a 50-year period of observation. These data were used to carry out a regionalization of Kamchatka's seismic volume and adjacent areas. In all, ten zones were identified with differing activities and origins of seismicity. A comparative analysis was carried out for the seismicity in the more active zones. We found significant differences between the structures of the southern and the northern segment in the Kamchatka part of the Kuril-Kamchatka subduction zone. Seismological data corroborated a relationship between the subduction zone and the underthrusting of the Pacific plate under the Eurasian plate. These data from the 50-year period of observation helped identify a new Koryak seismic belt that encompasses the northwestern coast of the Bering Sea. We provide a brief review of macroseismic effects due to the most significant earthquakes for the 1962-2010 period. [ABSTRACT FROM AUTHOR]

The extensional South Tibetan fault system (STFS) crops out for more than 2000 km along the length of the Himalayan range crest. Interpretations of the signifi cance of this structure in Himalayan tectonics vary. While many regard it as rooted northward beneath Tibet, with offset estimates ranging as high as >200 km, others regard it as a relatively minor, rootless structure. Such inconsistent interpretations are possible because, except for the Everest region, where glacial erosion has exposed a cross section of the STFS, there are few direct constraints on the amount of slip on this feature. Arguments for very large displacements have been based on indirect lines of evidence (e.g., geothermobarometric data) that are multiply interpretable. However, new fi eld work and remote sensing data reported here directly support the petrologic arguments for large displacements, at least in the eastern Himalaya. Near the western boundary of Bhutan, the trace of the STFS is apparently offset ~70 km across a NNE-SSW--trending graben, the Yadong cross structure. This offset has been attributed by previous authors to left-lateral slip along the Jomolhari fault system, which bounds the eastern edge of the graben. In fact, the basal structure of the STFS is not offset, but forms a regionally continuous low-angle detachment surface. The outcrop pattern of the structure, kinematic indicators in fault-related tectonites, and the lack of matchable correlative hanging wall and footwall units require a minimum displacement of ~65 km for the detachment. Such displacements are comparable with estimates for major contractional structures in the eastern Himalaya, such as the Main Central thrust system, and confirm the importance of STFS extension in the evolution of the orogenic system. [ABSTRACT FROM AUTHOR]

We present balanced and restored cross-sections across the Western Cuba fold and thrust belt, based on MCS profiles, field data and balancing techniques. The cross-section intersects the Los Palacios Basin, the Sierra del Rosario antiformal stack, the Bahía Honda unit, the frontal imbricated thrust sheets, the foredeep basin and a buried, geometrically inferred duplex. The minimum calculated shortening is 130 km. Syntectonic deposits and a forward kinematic model provide a good constraint for the Cenozoic tectonic evolution of the orogen, from the emplacement of the Bahía Honda unit to the final infill of the foredeep. [ABSTRACT FROM AUTHOR]