Search

The complete evolutionary process of orogenesis can be deciphered by studying metamorphic rocks at middle and lower crustal depths of orogens. Recent studies have suggested that granulite-facies metamorphic rocks in the Paleoproterozoic Jiao–Liao–Ji orogenic belt experienced clockwise pressure–temperature (p–T) paths. However, due to the effects of high temperature, the prograde metamorphic processes are poorly constrained. The question could be solved by studying the Barrovian series rocks, because some garnet growth zoning has been preserved in the lower grade rocks. A Barrovian series from garnet to kyanite-sillimanite zones has been recognized in the Liaodong Peninsula. Based on petrology and mineral chemistry, each metamorphic rocks in metamorphic zone are divided into prograde, peak, and retrograde metamorphic stages. Pseudosection modelling constrains the peak metamorphic conditions at ~568°C and ~5.8 kbar for the garnet zone, ~585°C and ~6 kbar for the staurolite zone, and ~670°C and ~8.2 kbar for the kyanite-sillimanite zone. All Barrovian series rocks have clockwise p–T paths, implying crustal thickening during prograde metamorphism. LA-ICP-MS monazite and zircon U–Pb dating suggest that peak Barrovian metamorphism occurred at ca. 1.92–1.91 Ga. Combining our results of the Barrovian series with studies on granulite-facies metamorphic rocks, we suggest that the Jiao–Liao–Ji belt experienced crustal thickening from 1.95 to 1.90 Ga, inducing Barrovian metamorphism and granulite-facies metamorphism in the middle and lower crust, respectively. Subsequently, rocks located at the different crustal levels were exhumed during post-orogenic extension. [ABSTRACT FROM AUTHOR]

Thermobarometry in the Northern Snake Range metamorphic core complex (Nevada, USA) implies pre‐extensional burial of footwall rocks to 21–30 km depths, while geologic field relationships support 7–13 km pre‐extensional depths. This has fueled a 40‐year‐long debate, which has far‐reaching implications for how pressure data are interpreted in orogenic settings. Here, we test published models for deep burial by integrating regional cross‐section reconstructions with new (n = 95) and published (n = 132) peak temperature measurements, field relationships and published geophysical data. Burial of Neoproterozoic‐Cambrian metasedimentary footwall rocks to 21–30 km depths is incompatible with a regional seismic reflection cross‐section that interprets the top of Precambrian crystalline basement at 17–20 km depths. Two reconstructed cross‐sections define 42 km and 50–65 km of displacement on the master detachment fault and demonstrate that the higher displacement ranges (>66–94 km and >76–102 km, respectively) necessary to exhume rocks from 21 to 30 km depths are not possible without spatially overlapping Cambrian rocks preserved in its footwall and hanging wall. The 22°C/km average Late Cretaceous thermal gradient predicted by thermobarometry is incompatible with the 46 ± 10°C/km Late Cretaceous peak thermal gradient that we calculate down to 15–20 km pre‐extensional depths. Field relationships that rule out large‐magnitude shortening invalidate models for deep footwall burial via thrust or reverse faulting. We conclude that there is no scenario for deep burial that is compatible with structural/geophysical constraints, crustal thermal architecture, and field relationships. This necessitates a non‐lithostatic interpretation for pressures from the Northern Snake Range, similar to recent interpretations for other Cordilleran metamorphic core complexes. Key Points: Strain compatibility demonstrates that the detachment displacement necessary to exhume footwall rocks from 21 to 30 km depths is not possibleThe 22°C/km gradient predicted by thermobarometry is incompatible with the Late Cretaceous thermal gradient of 46 ± 10°C/km that we calculateA non‐lithostatic interpretation for pressure data from the Northern Snake Range is required, similar to other Cordilleran core complexes [ABSTRACT FROM AUTHOR]

[Display omitted] • A regional geology systematic review based on cross-sections and space–time diagrams. • The Dom Feliciano Belt orogenic cycle records pre-, syn- and post-collisional stages. • PT-paths are characteristic of hinterland and foreland tectonic domains. • Northern DFB foreland rifting contrasts with central DFB active margin in the Tonian. • The symmetric schismogenesis of West Gondwana Orogen models can be conciliated. The Dom Feliciano Belt evolution is reviewed based on cross-sections, space–time diagrams, P-T paths, and Sr–Nd isotopic data of pre-collisional metaigneous rocks. The belt is divided into northern, central and southern sectors, subdivided into tectonic domains, developed at Neoproterozoic pre-, syn- and post-collisional stages. The northern sector foreland pre-collisional setting represents a rift, with tholeiitic (meta)volcanic rocks (∼800 Ma) chronocorrelated to hinterland intermediate and acidic orthogneisses of high-K calc-alkaline arc signature. In contrast, the central sector records a complete section from the forearc towards the back-arc region during pre-collisional times. In the western domain, ophiolites (∼920 Ma) are associated with arc-related orthogneisses and metavolcanic rocks (880–830 Ma; 760–730 Ma). At back-arc position, continental arc-related magmatism (800–780 Ma) is registered by hinterland orthogneisses and central foreland metavolcanic rocks. Ophiolites on the hinterland opposite side comprise two compositional groups, with N-MORB and supra subduction signature, interpreted as a back-arc basin record (∼750 Ma). The pre-Neoproterozoic basement of the whole belt is correlated with the Nico Perez Terrane and Luis Alves Block (Archean to Mesoproterozoic, with Congo Craton affinity). This contrasts with the Piedra Alta Terrane (Rio de La Plata Craton, only Paleoproterozoic), westernmost Uruguay. The suture between the Piedra Alta and Nico Perez terranes is correlated with the suture zone in the westernmost central sector. Transpression affected both foreland and hinterland during collision (660–640 Ma), with high-T/low-P hinterland progressive exhumation, whilst foreland low- to medium-grade correlated sequences record underthrusting. Post-collisional processes included magmatism throughout the belt (640–580 Ma), strain partitioning along strike-slip shear zones, and foreland basin fill. Late tectono-metamorphic and magmatic processes (560–540 Ma) were attributed to the Kalahari Craton collision. Arc magmatism migration due to subduction angle variations suggests modern-style plate tectonics during Gondwana amalgamation. Diachronism and kinematic inversion are characteristic of an oblique convergent multi-plate orogenic system. [ABSTRACT FROM AUTHOR]

Lithospheric foundering is hypothesized to contribute to the formation of Earth's largest continental plateaus, but the predicted effects remain poorly constrained, especially considering variations in crustal strength. Here we propose that lithospheric foundering involving a hot, weak crust can explain aspects of topography and crustal deformation in mountain belts. We explore this hypothesis using numerical models of orogenesis and foundering in the Southern Puna Plateau in the Central Andes. Contrary to previous models of foundering involving a strong crust, which are characterized by subsidence and shortening, a weak crust results in surface uplift and upper‐crustal horizontal extension, which is accommodated by horizontal shortening in peripheral regions. Our model explains data such as the timing and location of exhumation and basin sedimentation as a response to foundering. The model also shows that foundering is capable of converting a high‐relief, broken‐foreland region into a high‐elevation, low‐relief plateau in a convergent tectonic setting. Plain Language Summary: Thickened crust can gravitationally unstable and founder into the mantle. This process could contribute to the formation of large plateaus such as Tibet and the Central Andes, which are composed of hot, felsic, and therefore weak crust. However, existing models have not thoroughly considered the implications of lithospheric foundering beneath a weak crust. We present numerical modeling experiments that show that a lithospheric drip can cause crustal flow and spreading, even when it takes place within a convergent tectonic setting, such as a major mountain belt. By comparing our models to geologic data from the Central Andes, we suggest that this scenario can explain many intriguing geological puzzles within the Puna Plateau, such as the timing and distribution of horizontal extension, the thickening of the crust, and the uplift history of the plateau. Future studies should consider the possibility of a weak, flowing crust during a lithospheric foundering event. Key Points: Lithospheric foundering under a hot, weak crust causes syn‐convergent, upper‐crustal extensionOur models successfully explain the Cenozoic uplift and deformation of the Puna Plateau as a result of this processThis style of foundering has been overlooked but may apply to other large orogens [ABSTRACT FROM AUTHOR]

Structural elements of the Svecokarelide pericratonic zone in the Karelian Massif (SE Fennoscandia) were identified and described. They were formed after the major events of the Svecofennian tectogenesis. The age ranges of the orogenic stage and the post-orogenic extension collapse were dated, and the depth levels of the corresponding structures were determined. The differentiated exhumation process of deep complexes of the post-Proterozoic Savo–Ladoga movable zone was visualized. The approximate exhumation velocities of the deep material were estimated at certain stages of Precambrian evolution in the zone under consideration. [ABSTRACT FROM AUTHOR]

The Porgera Transfer Zone (PTZ) is a major crustal and probably lithospheric structure across Papua New Guinea recording >50 km offset of ophiolites and very different patterns of geology and topography on either side. In the Late Jurassic, the PTZ probably separated oceanic crust and thick Jurassic Om shales to the west from a continental promontory to the east. During the Late Miocene to Recent orogenesis, the differential compression of these features is interpreted to have created a dextral strike slip fault across the fold belt with pull-apart basins at sites of fault relays. This facilitated the ascent of intrusions and mineralization at Porgera. The acquisition of high-resolution LIDAR data semi-regionally around the Porgera Gold Mine greatly improved interpretation of the regional geology and particularly the recognition of normal faults. By correlating with sparse dip data and paly-dated samples, it was possible to create stratigraphic sections and interpret structural cross-sections using the LIDAR data. As the area involved strike–slip offsets, it was important to construct sections in multiple orientations in order to interpret the 3D geology. Both dips and fault orientation could be directly inferred from the LIDAR data such that sections could be constructed orthogonally to them. A balanced, restored and forward-modelled cross-section illustrates the interaction between thrust faults and normal faults during compression and that it was synchronous with the development of a pull-apart basin. A semi-regional 3D geological model, which was developed mainly from the LIDAR data, supports the hypothesis of inversion of the thick Om beds to the west before or during compression of the continental promontory to the east resulting in dextral strike–slip offsets across the PTZ. A jog or relay in the faults occurred and caused a pull-apart collapse basin to develop in the area of the Porgera mine. Similar pull-apart graben, or negative flower structures, were detected nearby and may be areas for future exploration. [ABSTRACT FROM AUTHOR]

Copyright of World Nuclear Geoscience is the property of World Nuclear Geoscience Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Continental orogens that involve subduction and collision are important target areas for studying the growth, stabilization and transformation of Earth's continents. In particular, the nature of the lithospheric mantle and its relationship to the overlying crust in these active subduction-collision zones are key factors to be constrained. Mantle xenoliths entrained by Cenozoic basalts from the Indochina Block, the Sukhothai Arc and the Inthanon Zone (IB-SA-IZ) provide direct deep-seated samples of the lithospheric mantle derived from part of the Tethyan orogenic belt, offering a unique opportunity to study mantle processes during orogenesis in response to the closure of the Paleo-Tethys Ocean. The studied mantle xenoliths comprise 32 spinel lherzolites, six harzburgites, and one olivine websterite. We present a comprehensive study of the elemental geochemistry and Os isotopes of this sample suite. Their lithophile element systematics indicate that they represent mantle residues after varying degrees of melt extraction (5–24%), followed by melt refertilization. Although the highly siderophile element abundances have been affected to some extent by melt refertilization through removal of sulfides, the Os isotopic compositions of the studied xenoliths were minimally disturbed. Lherzolites and the sole olivine websterite from the IB-SA-IZ share similar Re-Os isotope systematics (187Os/188Os: 0.121–0.137) to global abyssal peridotites, representing juvenile lithospheric mantle accreted from the upwelling asthenosphere, most likely associated with arc-continent collision in response to the closure of the Paleo-Tethys Ocean and back-arc basin during the Middle-Late Triassic. In contrast, the refractory harzburgites from the Indochina Block and Sukhothai Arc are characterized by substantially lower 187Os/188Os ratios (187Os/188Os: 0.117–0.122) than the lherzolites, yielding Mesoproterozoic Re-depletion Os model ages, which can be interpreted as either ancient lithosphere relics beneath these regions or accreted ancient mantle debris from the upwelling asthenosphere. Although the interpretation for the origin of the older harzburgites is ambiguous, we can conclude that rejuvenation of the lithospheric mantle commonly occurred beneath different tectonic units of the Tethyan orogenic belt: i.e., the pre-existing lithospheric mantle beneath different tectonic units of the Tethyan orogenic belt has been largely replaced by upwelling asthenospheric mantle during the Middle-Late Triassic orogenesis. This mantle was then further refertilized to varying degrees by asthenosphere-derived melts. Both processes play key roles in defining the nature of the lithospheric mantle in orogenic settings. This study also highlights that the geodynamic processes in the lithospheric mantle beneath orogenic belts can be well constrained by integrated evidence from lithophile and highly siderophile elements and their isotopes (e.g., Os isotopes) of mantle xenoliths. [ABSTRACT FROM AUTHOR]

Abstract Lithospheric foundering is hypothesized to contribute to the formation of Earth's largest continental plateaus, but the predicted effects remain poorly constrained, especially considering variations in crustal strength. Here we propose that lithospheric foundering involving a hot, weak crust can explain aspects of topography and crustal deformation in mountain belts. We explore this hypothesis using numerical models of orogenesis and foundering in the Southern Puna Plateau in the Central Andes. Contrary to previous models of foundering involving a strong crust, which are characterized by subsidence and shortening, a weak crust results in surface uplift and upper‐crustal horizontal extension, which is accommodated by horizontal shortening in peripheral regions. Our model explains data such as the timing and location of exhumation and basin sedimentation as a response to foundering. The model also shows that foundering is capable of converting a high‐relief, broken‐foreland region into a high‐elevation, low‐relief plateau in a convergent tectonic setting.

The Porgera Transfer Zone (PTZ) is a major crustal and probably lithospheric structure across Papua New Guinea recording >50 km offset of ophiolites and very different patterns of geology and topography on either side. In the Late Jurassic, the PTZ probably separated oceanic crust and thick Jurassic Om shales to the west from a continental promontory to the east. During the Late Miocene to Recent orogenesis, the differential compression of these features is interpreted to have created a dextral strike slip fault across the fold belt with pull-apart basins at sites of fault relays. This facilitated the ascent of intrusions and mineralization at Porgera. The acquisition of high-resolution LIDAR data semi-regionally around the Porgera Gold Mine greatly improved interpretation of the regional geology and particularly the recognition of normal faults. By correlating with sparse dip data and paly-dated samples, it was possible to create stratigraphic sections and interpret structural cross-sections using the LIDAR data. As the area involved strike–slip offsets, it was important to construct sections in multiple orientations in order to interpret the 3D geology. Both dips and fault orientation could be directly inferred from the LIDAR data such that sections could be constructed orthogonally to them. A balanced, restored and forward-modelled cross-section illustrates the interaction between thrust faults and normal faults during compression and that it was synchronous with the development of a pull-apart basin. A semi-regional 3D geological model, which was developed mainly from the LIDAR data, supports the hypothesis of inversion of the thick Om beds to the west before or during compression of the continental promontory to the east resulting in dextral strike–slip offsets across the PTZ. A jog or relay in the faults occurred and caused a pull-apart collapse basin to develop in the area of the Porgera mine. Similar pull-apart graben, or negative flower structures, were detected nearby and may be areas for future exploration.

Cordilleran orogens are complex tectonic systems, strongly influenced by lithospheric deformation and exhumation. However, in the type region of the Central Andes, the timing and mechanisms of deformation and mountain building remain poorly constrained, especially for the high‐elevation Puna Plateau of NW Argentina. We use geologic mapping, structural cross‐sections, low‐temperature thermochronology, and U‐Pb dating of ash and detrital zircons to elucidate the history and style of orogenic deformation in the Antofalla region of the Puna Plateau. Cooling ages of major reverse fault hanging walls and dated growth strata indicate that crustal shortening activated major reverse faults during the Eocene and continued out‐of‐sequence through the Early Miocene. This protracted period of shortening, which resulted in the filling of the Antofalla Basin, was followed by a transient episode of upper‐crustal E‐W extension on a major normal fault system during the Late Miocene. Pliocene to Quaternary time saw E‐W shortening return to the region. Our structural cross‐section permits only a low magnitude of shortening (∼15–25%), which stands in contrast to the 60‐km thick crust. Triassic to Cretaceous cooling ages from footwall rocks and minor structures indicate that the entire region experienced little exhumation or sedimentation during the Mesozoic, perhaps retaining a crust thickened during multiple episodes of Paleozoic orogenesis. The crust may also reflect lower‐crustal thickening due to the growth of a lithospheric drip during the Late Miocene. Key Points: Combination of structural mapping, thermochronology, and U‐Pb chronostratigraphy reveals four phases of Cenozoic deformationExhumation due to horizontal shortening was underway by the Eocene (∼45 Ma), ∼20 Myr earlier than previously inferred for the regionShortening propagated out‐of‐sequence, westward from the Calalaste Range into the Antofalla Basin until ∼15 Ma [ABSTRACT FROM AUTHOR]

Four Tethyan ocean basins are recognised in Asia, the Proto-Tethys (Late Proterozoic - Silurian), Palaeo-Tethys (Middle Devonian - Late Triassic), Meso-Tethys (Middle Permian - Late Cretaceous) and Ceno-Tethys (late Middle Triassic - Eocene). Multi-disciplinary data, including ages of pelagic sediments, ocean plate stratigraphy, seamounts, ophiolites, blueschists, eclogites in accretionary complexes, volcanic arc and magmatic rocks found along suture zones of the Tethyan oceans are described and used to date the opening and closure of these oceans. The evolution of the Tethyan ocean basins in Asia illustrates that Asia has been a giant convergent zone for more than 500 million years and the Phanerozoic construction and evolution of Asia involved the opening and closure of Tethyan ocean basins and the collision and accretion of Gondwana-derived continental blocks and the Indian Craton. Subduction processes, arc and back-arc basin generation, and continent-continent and arc-continent collisions led to the principal orogenic events, basin development and related mineral and energy resource deposits recorded in Asia. Three major orogenic belts are recognised in Asia, the Central Asian Orogenic Belt, that relates to the evolution of the Palaeo-Asia Ocean, and the Tethyan (Tethysides) Orogenic Belt and the Alpine-Himalayan Orogenic Belt which relate to the evolution of Tethyan ocean basins. The principal Tethyan basin related orogenies in Asia are the Bhimphedian Orogeny (Ordovician-Silurian) that reflects the collision of major Asian continental blocks ("Asian-Hun Superterrane") with Gondwana, the Indosinian (Cimmerian) Orogeny (Permian-Triassic) resulting from Palaeo-Tethyan subduction processes, collisions of Asian blocks and collision of the Cimmerian continent with Asia, and the Himalayan-Tibetan Orogeny (Cretaceous-Palaeogene) caused by subduction of the Meso- and Ceno-Tethys oceans and the Lhasa-Asia and India-Asia collisions. [Display omitted] • Proto-, Palaeo-, Meso-, and Ceno-Tethys oceans are recognised in Asia. • Orogeny was driven by subduction/closure of Tethyan oceans and collision of blocks. • Tethyan & Alpine-Himalayan orogenic belts relate to evolution of Tethyan oceans. [ABSTRACT FROM AUTHOR]

Metamorphic timescales harbor crucial information for quantifying lithospheric processes and identifying tectonic regimes. The Orosirian Period is known for global orogenesis during 2.1‒1.8 Ga that possibly signifies the emergence of global-scale plate tectonics. While the metamorphic pressure–temperature (P–T) paths and T/P ratios have been extensively used to characterize 2.1–1.8 Ga orogens, their detailed metamorphic timescales remain underutilized. In this study, we use garnet diffusion modeling to explicitly explore the metamorphic timescales of dominant pelitic granulites in the Jiaobei terrane, the southwest part of the Jiao-Liao-Ji orogenic belt (JLJB), North China Craton. The pelitic granulites record high-pressure granulite-facies metamorphism of 13–14 kbar and 860–870 °C, followed by fast decompression (4‒21 mm yr−1) with some degree of heating to medium-pressure granulite-facies retrogression of 7‒8 kbar and 865‒950 °C at c. 1.85 Ga. The subsequent cooling is nearly isobaric, but likely nonlinear with initially faster and later slower cooling (17‒32 °C Myr−1, 950/865–700 °C; 5–7 °C Myr−1, 700–600 °C, respectively). The determined clockwise P–T–t path provides evidence for convergent plate boundary processes and the fast exhumation is likely related to an extensional setting. The relatively fast exhumation and cooling rates at high temperatures, as obtained via diffusion chronometry, represent the fastest rates yet reported from 2.1 to 1.8 Ga orogens and are several times to one order of magnitude slower than those observed in modern orogens. In the light of recent numerical modeling, we suggest that these slower metamorphic rates of the c. 2.1‒1.8 Ga JLJB orogenic rocks are consistent with the features of orogenesis occurring at higher mantle temperatures, such as hotter orogenic thermal structures, less over-thickened orogenic crusts, and distributed strain patterns. Therefore, the timescale information from the JLJB indicates that Paleoproterozoic plate tectonics under higher temperatures might have caused subduction and collisional orogenesis to be distinct from their modern style. Notably, the detailed ancient metamorphic timescales achieved by diffusion modeling cannot be resolved geochronologically, highlighting the necessity of applying diffusion chronometry to quantify ancient tectonic processes. [ABSTRACT FROM AUTHOR]

The Himalaya are among the youngest and highest mountains in the world, but the exact timing of their uplift and origins of their biodiversity are still in debate. The Himalayan region is a relatively small area but with exceptional diversity and endemism. One common hypothesis to explain the rich montane diversity is uplift-driven diversification—that orogeny creates conditions favoring rapid in situ speciation of resident lineages. We test this hypothesis in the Himalayan region using amphibians and reptiles, two environmentally sensitive vertebrate groups. In addition, analysis of diversification of the herpetofauna provides an independent source of information to test competing geological hypotheses of Himalayan orogenesis. We conclude that the origins of the Himalayan herpetofauna date to the early Paleocene, but that diversification of most groups was concentrated in the Miocene. There was an increase in both rates and modes of diversification during the early to middle Miocene, together with regional interchange (dispersal) between the Himalaya and adjacent regions. Our analyses support a recently proposed stepwise geological model of Himalayan uplift beginning in the Paleocene, with a subsequent rapid increase of uplifting during the Miocene, finally giving rise to the intensification of the modern South Asian Monsoon. [ABSTRACT FROM AUTHOR]

Deciphering the relationship between polyphase tectonic foliations and their associated mineral assemblages is significant in understanding the process from diagenesis to low‐/medium‐/high‐grade metamorphism. It can provide information related to strain, metamorphic conditions and overprinting relationships and so help reveal the tectonic evolution of orogenesis. In this study, we predominately focus on the formation of foliations and their related minerals, as developed in two separate basins. First of all, two stages of axial plane cleavages (S1 and S2) were recognized in the Hongyanjing inter‐arc basin, the formation of the S1 axial plane cleavage is associated with mica rotation and elongation in mudstones in the local area. The pencil structure of S2 formed during the refolding phase, the minerals in the sedimentary rocks not changing their shape and orientation. Secondly, in the Liao‐Ji backarc basin, foliations include diagenetic foliation (bedding parallel foliation), tectonic S1 foliation (secondary foliation or axial plane cleavage of S0 folding) and crenulation cleavage (S2). The formation mechanism of foliation changes from mineral rotation or elongation and mineral solution transfer in S1 to crystal‐plastic deformation, dynamic recrystallization and micro‐folding in S2. Many index metamorphic minerals formed from low‐grade to medium‐grade consist of biotites, garnets, staurolite and kyanite, constituting a typical Barrovian metamorphic belt. Accordingly, a new classification of foliation is presented in this study. The foliations can be divided into continuous and disjunctive foliations, based on the existence of microlithons, detectable with the aid of a microscope. Disjunctive foliation can be further sub‐divided into spaced foliation and crenulation cleavage, according to whether (or not) crenulation (micro‐folding) is present. The size of the mineral grains is also significant for classification of the foliations. [ABSTRACT FROM AUTHOR]

The Trans‐Hudson orogen (THO) is one of the best‐preserved Proterozoic orogens on Earth, largely unaffected by subsequent tectonism, yet its southern extent lies concealed beneath the North American Central Plains. A new 3D resistivity model over the southern orogen is developed and interpreted alongside borehole, potential field, and seismic reflection data. We present the first synoptic crustal view of the southern THO and a new tectonic model of the orogen. Our model reveals high‐conductivity belts marking paleo‐subduction zones while the orogen center consists of deeply exhumed relatively dense and mostly magnetic juvenile crust preserved between the deformed margins of the Wyoming and Superior cratons. Complex structure along the western margin suggests convergence began with oblique subduction and the northward transport of severed fragments of the Wyoming Province. High‐conductivity belts are in places offset from upper‐crustal geophysical boundaries, consistent with the thrusting of accreted arcs over the Archean margins during terminal closure. Plain Language Summary: Ancient orogens, the remnants of past mountain ranges, mark the location of tectonic plate collisions. The Trans‐Hudson orogen (THO) is a particularly well preserved orogen, but much of its southern portion is concealed beneath the North American Central Plains. A new 3D resistivity model over the southern orogen is developed and interpreted alongside other geological and geophysical data. We present the first synoptic crustal view of the southern THO and a new tectonic model constrained by all existing data. Our models reveal deep‐crustal high‐conductivity belts marking the location of past subduction. The geometry of these belts suggests a previously unrecognized early stage of convergence during which fragments of the Wyoming craton were transported along the edge of the orogen. Key Points: The Trans‐Hudson orogen (THO) is bordered by two high‐conductivity belts marking paleosubduction zones of opposite polarityThe southern THO consists of deeply exhumed juvenile arc terranes and fragments of the Wyoming cratonGeophysical data indicate convergence began along a transpressive margin with considerable along‐strike transport [ABSTRACT FROM AUTHOR]

[Display omitted] • Three phases of deformation (D 1 -D 3) are recognized in the Langzishan Barrovian metamorphic series. • The kyanite zone rocks record a clockwise P-T-D path in the Paleoproterozoic. • Metamorphic and deformational characteristics documented by Barrovian metamorphic series in the Paleoproterozoic and Phanerozoic are comparable, possibly indicating a similar orogenic mechanism. Orogenesis always involves multiple tectonic events accompanied by metamorphic cycles. The Barrovian metamorphic series often records complicated prograde metamorphism and deformational features, which are crucial for understanding the related orogenic evolution. While Barrovian metamorphism have been widely documented in the Phanerozoic orogenic belts, limited stuides have been conducted on Paleoproterozoic Barrovian metamorphic series. In this contribution, Barrovian metamorphic series extending from biotite to kyanite zones in the middle of Jiao-Liao-Ji Orogenic Belt (JLJOB) from eastern part of North China Craton (NCC) was investigated. The current studies identified the occurrence of polyphase deformation and metamorphism within the Langzishan Barrovian metamorphic series. D 1 fabrics are characterized by the development of S 1 foliation and L 1 lineation in association with greenschist facies metamorphism (M 1) that occurrs at ca. 490 ℃ and ca. 5.7 kbar. D 2 fabrics that include different folds (F 2), S 2 crenulation cleavage, S 2 foliation and L 2 lineation, accompanied by the low amphibolite metamorphism (M 2) that occurrs at ca. 670 ℃ and 8.2–8.6 kbar. D 3 fabrics involving kink band postdate sillimanite growth that occurrs at ca. 660 ℃ and ca. 6.5 kbar, and predate chlorite occurrence. Monazite U-Pb dating suggests the peak and retrograde metamorphic ages of ca. 1.93 Ga and 1.86 Ga, respectively. Thus, a clockwise pressure–temperature-time-deformation (P-T-t-D) path is established, possibly related to the crustal thickening process. These features are very similar to those documented in Phanerozoic Barrovian metamorphic series, suggesting that a comparable orogenesis mechanism could be shared in the Paleoproterozoic and Phanerozoic. [ABSTRACT FROM AUTHOR]

The pressure-temperature-time (P-T-t) evolution of metamorphic rocks is directly related to geodynamics as different tectonic settings vary in their thermal architecture. The shapes of P-T paths and thermobaric ratios (T/P) of metamorphic rocks have been extensively used to distinguish different tectonic domains. However, the role of metamorphic timescales in constraining tectonic settings remains underutilized. This is because of the poorly understood relationship between them, and the difficulty in accurately constraining the onset and end of a particular metamorphic event. Here, we show why and how the intrinsic relationship between thermal regime, rheology and rate of motion controlled by the heat, mass and momentum conservation laws translate to differences in heating, cooling, burial, exhumation rates of metamorphic rocks and thereby, to the duration of metamorphism. We compare the P-T-t paths of the orogenic metamorphic rocks of different ages and in particular, analyse their retrograde cooling rates and durations. The results show that cooling rates of the metamorphic rocks are variable but are dominantly <50 °C/Ma during most of the Precambrian before increasing by an order of magnitude (>100 °C/Ma) during the late Neoproterozoic to Phanerozoic. To seek what controlled this secular change in metamorphic cooling rates, we use thermomechanical modelling to calculate the P-T-t paths of crustal rocks in different types of continental orogenic settings and compare them with the rock record. The modelled P-T-t paths show that lithospheric peel-back driven orogenic settings, which are postulated as an orogenic mode operating under the hotter mantle conditions of late Archean to early Proterozoic, are characterised by longer durations of metamorphism and slower cooling rates (a few 10s of °C/Ma) as compared to the modern orogenic settings (a few 100s of °C/Ma) operating under relatively colder mantle conditions. This is because peel-back orogens feature: (1) hot lithospheres with very high crustal geotherms being sustained by high mantle heat-flow and profuse magmatism, and (2) distributed deformation patterns that limit vertical extrusion (exhumation) of the metamorphic rocks along localized deformation zones and instead, trap them in the orogenic core for a long time. In contrast, modern orogens mostly involve colder lithospheres and allow rapid exhumation through localized deformation, which facilitates faster cooling of hot, exhumed metamorphic rocks in a colder ambience. Thus, we propose that the secular change in metamorphic cooling rates indicates a changing regime of orogenesis and thereby, of plate tectonics through time. Predominance of the slower metamorphic cooling rates before the Neoproterozoic indicate the occurrences of peel-back orogenesis and truncated hot (collisional) orogenesis during that time, while the appearance of faster cooling rates since the late Neoproterozoic indicates the transition to modern style of orogenesis. A transition between these orogenic styles also accounts for the prolonged longevity (>100 million years) of many Precambrian orogenic belts as compared to the Phanerozoic ones. This study underscores the strength of timescales in combination with P-T paths to distinguish tectonic settings of different styles and ages. [Display omitted] • Metamorphic cooling rates show a secular change. • Cooling rates were slower until the late Neoproterozoic • Changing styles of orogenesis explains this change in cooling rates. • Distributed deformation in Precambrian orogens account for the slowercooling • Localized deformation in modern orogens facilitate faster cooling. [ABSTRACT FROM AUTHOR]

Mountain height at convergent plate margins is limited by the megathrust shear force, but it remains unclear how this constraint affects the topographic evolution and mountain building at the transition from subduction to collision. Generally, mountain height increases during the subduction‐collision transition in response to crustal thickening or processes like mantle delamination and slab breakoff, but the main parameters controlling how much mountain height increases remain poorly understood. Here we show, based on analytical and finite‐element force‐balance models, that the increase in mountain height depends on the magnitude of the megathrust shear force and the reduction of submarine margin relief. During the subduction stage, the shear force is balanced by the gravitational effect of the margin relief and the deviatoric stresses in the upper plate are low. When the submarine margin relief is reduced during the closure of the ocean basin, the effect of the gravitational force decreases and the upper plate experiences enhanced deviatoric compression, which allows the mountain height to increase until a near‐neutral stress state beneath the high mountains is restored. If the increase in mountain height cannot keep pace with the submarine relief reduction, the compression of the upper plate increases by a few tens of MPa, which promotes tectonic shortening and mountain building. Our analysis implies that mountain height can increase by hundreds of meters to a few kilometers during collision, depending primarily on the trench depth during the subduction stage and possible syncollisional changes of the megathrust shear force. Key Points: Force balance requires an increase in mountain height when submarine relief is reduced at the subduction‐collision transitionThe required increase is several hundred meters to a few kilometers depending mainly on the trench depth and the shear force magnitudeA delayed increase in mountain height relative to onset of collision increases the upper‐plate compression and supports mountain building [ABSTRACT FROM AUTHOR]

Many orogens on the planet result from plate convergence involving subduction of a continental margin. The lithosphere is strongly deformed during mountain building involving subduction of a plate composed generally of accreted continental margin units and some fragments of downgoing oceanic crust and mantle. A complex deformation involving strong partitioning of deformation modes and kinematics produces crustal shortening, accompanied by crustal thickening. Partitioning depends on three main factors: (1) rheologic layering of the lithosphere; (2) interaction between tectonics and surface processes; (3) subduction kinematics and 3D geometry of continental margins (oblique convergence, shape of indenters). Here we present an original view and discussion on the impact of deformation partitioning on the structure and evolution of orogens by examining the Taiwan mountain belt as a case study. Major unsolved questions are addressed through geological observations from the Taiwan orogen and insights from analogue models integrating surface processes. Some of these questions include: What is the role played by décollements or weak zones in crustal deformation and what is the impact of structural heterogeneities inherited from the early extensional history of a rifted passive continental margin? What is the relationship between deep underplating, induced uplift and flow of crustal material during erosion (finite strain evolution during wedge growth)? Are syn-convergent normal faults an effect of deformation partitioning and erosion? What is the role of strain partitioning on the location of major seismogenic faults in active mountain belts? What can be learned about the long-term and the present-day evolution of Taiwan? [ABSTRACT FROM AUTHOR]

Documenting the processes that facilitate exhumation of ultrahigh‐pressure (UHP) rocks at convergent margins is critical for understanding orogen dynamics. Here, we present structural and temperature data from the Himalayan UHP Tso Morari nappe (TMN) and overlying nappes, which we integrate with published pressure‐temperature‐time constraints to refine interpretations for their structural evolution and exhumation history. Our data indicate that the 5.5‐km‐thick TMN is the upper portion of a penetratively deformed ductile slab, which was extruded via distributed, pure shear‐dominated, top‐down‐to‐east shearing. Strain in the TMN is recorded by high‐strength quartz fabrics (density norms between 1.74 and 2.86) and finite strain data that define 63% transport‐parallel lengthening and 46% transport‐normal shortening. The TMN attained peak temperatures of ~500–600°C, which decrease in the overlying Tetraogal and Mata nappes to ~150–300°C, defining a field gradient as steep as 67°C/km. Within the overlying nappes, quartz fabric strength decreases (density norms between 1.14 and 1.21) and transport‐parallel lengthening and transport‐normal shortening decrease to 14% and 18%, respectively. When combined with published 40Ar/39Ar thermochronometry, quartz fabric deformation temperatures as low as ~330°C indicate that the top‐to‐east shearing that exhumed the TMN continued until ~30 Ma. Peak temperatures constrain the maximum depth of the overlying Mata nappe to 12.5–17.5 km; when combined with published fission‐track thermochronometry, this provides further support that the TMN was not underplated at upper crustal levels until ~30 Ma. The long‐duration, convergence‐subnormal shearing that exhumed the TMN outlasted rapid India‐Asia convergence by ~15 Myr and may be the consequence of strain partitioning during oblique convergence. Key Points: Deformation temperatures combined with thermochronometry indicate that the shearing that exhumed the Tso Morari nappe continued until ~30 MaTop‐to‐east shearing outlasted rapid India‐Asia convergence by ~15 Myr and may be a result of strain partitioning in the western HimalayaThe exhumation of the Tso Morari nappe is generally consistent with models of UHP exhumation that emphasize piston forcing or recirculation [ABSTRACT FROM AUTHOR]

The results of 40Ar/39Ar dating of pseudotachylytes, first identified in the Paleoproterozoic zonally metamorphosed (greenschist to granulite facies) Ladoga complex of svecofennides, are presented. A wide age range of the formation of pseudotachylytes in the Riphean (1.59–1.31 Ga), presumably caused by the exhumation of deep rocks during the Svecofennian tectonogenesis and the subsequent orogenesis and riftogenesis in southeastern Fennoscandia, has been established. [ABSTRACT FROM AUTHOR]

Bhowmik suggested two stages of orogenesis at the southern margin of the Central Indian Tectonic Zone (CITZ): (a) an accretionary orogenesis type at ca. 1.6–1.5 Ga that formed a proto‐Greater Indian Landmass (GIL) through the assembly of arc, back‐arc and continental margins, (b) a Himalayan‐style continental collision event between 1.06 and 0.93 Ga that finally stitched the North and South India blocks to produce the final configuration of the GIL and (c) an intervening phase of extension between 1.5 and 1.06 Ga that led to the opening up of the Sausar Basin and deposition of the Sausar Group of rocks. [ABSTRACT FROM AUTHOR]

A Paleozoic subduction complex dominates the Mossman Orogen developed at the northern extremity of the Tasmanides, eastern Australia. Its southern part, displayed in the Broken River Province, is characterised by dismembered ocean-plate stratigraphy in which turbidite-dominated packages and widespread tectonic mélange development are characteristic. The Broken River complex is characterised by formations with quartzose sandstone alternating with those largely formed of sandstone of more labile character. The two compositional groups are considered to reflect separate, age-significant sedimentary regimes, but their ages have hitherto been poorly constrained. With the use of 1082 concordant detrital zircon ages from 13 samples we provide age control for the complex and track its sedimentary provenance. Of quartzose units, the Tribute Hills Arenite and Pelican Range Formation are late Cambrian–Early Ordovician, and the Wairuna Formation is Middle to Late Ordovician, in age. The more labile units (Greenvale, Perry Creek and Kangaroo Hills formations) are collectively of late Silurian–mid-Devonian age. Development of the complex spanned some 130 Myr. Continent-derived sediment involved in accretion of much the complex, from mid-Ordovician to mid-Devonian, was largely sourced from a nearby magmatic arc of late Cambrian–Devonian age, now represented by granitoid plutons of the Macrossan and Pama igneous associations. An older far-field Pacific-Gondwana sediment source is characteristic of early-phase (late Cambrian–Early Ordovician) accretion, in common with sedimentary units of this age generally developed in the Tasmanides. We consider the complex to have grown largely by underplating that positioned younger components beneath those that are older, with out-of-sequence thrust interleaving of these components occurring late in the accretionary history. A Late Devonian contractional folding and cleavage development (Tabberabberan orogenesis) is uniformly expressed across the entire complex and reflects an abrupt change in plate engagement with imposition of a compressional stress regime. [ABSTRACT FROM AUTHOR]

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

Resolving the timing of initiation and propagation of continental accretion associated with increasing topography and exhumation is a genuinely challenging task using low-temperature thermochronology. We present an integrated thermo-mechanical and low-temperature thermochronology modelling study of tectonically-inverted hyperextended rift systems. Model low-temperature thermochronology data sets for apatite (U-Th)/He, apatite fission-track, zircon (U-Th)/He and zircon fission-track systems, which are four widely used thermochronometric systems in orogenic settings, are generated from fourteen locations across a model collisional, doubly-vergent orogen. Our approach allows prediction of specific, distinct low-temperature thermochronology signatures for each domain (proximal, necking, hyperextended, exhumed mantle) of the two rifted margins that, in turn, enable deciphering which parts of the margins are involved in orogenic wedge development. Our results show that a combination of zircon (U-Th)/He and apatite fission-track data allows diagnostic investigation of model orogen tectonics and offers the most valuable source of thermochronological information for the reconstruction of the crustal architecture of the model inverted rifted margins. The two thermochronometric systems have actually very close and wide closure windows, allowing to study orogenic processes over a larger temperature range, and therefore over a longer period of time. Comparison of model data for inverted rifted margins with model data for non-inverted, purely thermally-relaxed rifted margins enables assessing the actual contribution of tectonic inversion with respect to thermal relaxation. We apply this approach to one of the best-documented natural examples of inverted rift systems, the Pyrenees. Similarities between our thermochronometric modelling results and published low-temperature thermochronology data from the Pyrenees provide new insights into the evolution of the range from rifting to collision. In particular, they suggest that the core of the Pyrenean orogen, the Axial Zone, consists of the inverted lower plate necking and hyperextended domains while the Pyrenean retrowedge fold-and-thrust belt, the North Pyrenean Zone, represents the inverted upper plate distal rifted margin (exhumed mantle, hyperextended and necking domains). This is in good agreement with previous, independent reconstructions from literature, showing the power that our integrated study offers in identifying processes involved in orogenesis, especially early inversion, as well as in predicting which domains of rifted margins are accreted during mountain building.

Questions on formation of modern geomorphological structure and flora of Mountain Dagestan are considered.

Abstract In this paper we present a series of thermo-mechanical experiments on continent-continent collision zones to investigate the role of lateral strength contrasts in terms of collision dynamics and orogen geometries. Our results show that differences in crustal rheology, may lead to a variety of different patterns of deformation and crustal geometries. Upper plate indentation forms a sequence of foreland propagating thrust units made of brittle upper crust on the lower plate. The strong deformation of the lower plate stands in stark contrast to the undeformed upper plate. In contrast, subduction of strong lithosphere beneath a weak upper plate forms a complex pattern of deformation. Deformation initiates on the lower plate and forms an antiformal stack made of brittle upper crust, before it indents the upper plate. Hence, deformation is present on both, the lower and upper plate, despite differences in initial strength. The outcome of this study has direct implications to natural collision zones, where differences in strength between the upper and lower plate exist. For example, along strike variability of upper vs. lower plate shortening in the Alps are likely to be controlled by contrasts in crustal strength. Furthermore, we suggest that the antiformal stack in the axial zone of the Pyrenees might indicate a strong lower plate at the onset of collision. Our results may therefore provide important constraints for the rheological state of continents during collision. Graphical abstract Image 1 Highlights • We study influences of crustal strength contrasts on continent-continent collision. • Crustal deformation always migrates from the stronger into the weaker plate with time. • Large-scale mountain geometries are controlled by crustal strength variations. [ABSTRACT FROM AUTHOR]

The geological framework and tectonics of the East Black Sea region is characterized through balancing a geological cross-section and paleoreconstruction during the Paleogene-Neogene period. The studied area includes the Kerch-Taman trough, the Anapa Swell (a continuation of the immersed part of the Greater Caucasus Orogen), the Tuapse trough, and the Shatsky Swell. This paper is mainly focused on the Russian shelf zone of the Black Sea. The results are important for understanding the trap formation time and the preservation of hydrocarbon deposits in the Russian sector of the Black Sea shelf. [ABSTRACT FROM AUTHOR]

Foliation Intersection/Inflection Axes within porphyroblasts (FIAs) provide a quantitative approach to microstructural and metamorphic analysis that can be used to integrate multiple deformation and metamorphic events and develop lengthy PT path histories during orogenesis. This paper reviews applications of FIAs for determining (1) porphyroblast rotation vs. nonrotation; (2) inclusion trail orientations and orogenic processes involving changes in the direction of bulk horizontal shortening; (3) in situ age determinations for multiple deformation episodes; (4) P-T-t-d paths of poly-metamorphism in an orogenic belt; and (5) constraining relative plate movement paths within ancient orogens. Quantitative structural and metamorphic data correlated directly to relative plate motions, are currently allowing the tectonic reconstruction of multiply deformed and metamorphosed terrains in orogens around the world. [ABSTRACT FROM AUTHOR]

The Qilian Block is one of many continental blocks involved in the early Paleozoic orogenesis of the Central China Orogen, which experienced complex interaction with adjacent blocks and orogens. In this study, we present zircon U-Pb-Hf isotopic, whole-rock elemental, and Sr-Nd isotopic data of the early-middle Silurian intrusive rocks in the Lanzhou-Baiyin regions, eastern part of the Qilian Block, to constrain their source and tectonic settings. The Houchangchuan granodiorite and Shichuan monzogranite were emplaced at ca. 437 Ma and ca. 428 Ma, respectively. These granitoids are peraluminous (A/CNK = 1.1-1.3), enriched in LREEs and LILEs (Rb, Th, U, Pb), depleted in HFSEs (Nb, Ta) with negative Eu and Sr anomalies, and have relatively high whole-rock εNd(t), −4.3 to −2.1, and zircon εHf(t), −10.9 to 1.1, values. The Shichuan monzonite is characterized by intermediate SiO2, metaluminous (A/CNK = ~0.8), and high LREEs fractionation with LILEs (Th, U, Pb) enrichment and HFSEs (Nb, Ta) depletion. We suggest the Houchangchuan granodiorite and Shichuan monzogranite were derived from the metasedimentary (metapelitic) source, which could be the Mesoproterozoic basement of the Qilian Block, and the mantle-derived materials injected into their source region. The Shichuan monzonite could have a mantle-derived origin. Integrated with data from previous studies, the early-middle Silurian (437-428 Ma) intrusive rocks in the eastern part of the Qilian Block were formed during the transition period from a syn-collisional to postcollisional setting, relating to the collisional process after the consumption of North Qilian Ocean (Proto-Tethys Ocean) in the northern margin of the Gondwana continent. [ABSTRACT FROM AUTHOR]

The eastern margin of North America has been shaped by several cycles of supercontinent assembly. These past episodes of orogenesis and continental rifting have likely deformed the lithosphere, but the extent, style, and geometry of this deformation remain poorly known. Measurements of seismic anisotropy in the upper mantle can shed light on past lithospheric deformation, but may also reveal contributions from present-day mantle flow in the asthenosphere. Here we examine SKS waveforms and measure splitting of SKS phases recorded by the MAGIC experiment, a dense transect of seismic stations across the central Appalachians. Our measurements constrain small-scale lateral variations in azimuthal anisotropy and reveal distinct regions of upper mantle anisotropy. Stations within the present-day Appalachian Mountains exhibit fast splitting directions roughly parallel to the strike of the mountains and delay times of about 1.0 s. To the west, transverse component waveforms for individual events reveal lateral variability in anisotropic structure. Stations immediately to the east of the mountains exhibit complicated splitting patterns, more null SKS arrivals, and a distinct clockwise rotation of fast directions. The observed variability in splitting behavior argues for contributions from both the lithosphere and the asthenospheric mantle. We infer that the sharp lateral transition in splitting behavior at the eastern edge of the Appalachians is controlled by a change in anisotropy in the lithospheric mantle. We hypothesize that beneath the Appalachians, SKS splitting reflects lithospheric deformation associated with Appalachian orogenesis, while just to the east this anisotropic signature was modified by Mesozoic rifting. [ABSTRACT FROM AUTHOR]

Although the Helvetic nappes of the Western Alps have been widely studied, their style, amount, and timing of deformation during the Alpine orogeny remain a subject of controversy. The discussion partly arises from various interpretations of the external crystalline massifs geometry and of the cover/basement relationships. Here, we apply structural analysis based on new field data, microtectonics, and 3D geological modeling on the Aiguilles Rouges and Mont-Blanc massifs, to better quantify their tectonic evolution and their relationship with the nappe stacking. Our results show large thrusting of the Helvetic Mesozoic sedimentary cover above the Aiguilles Rouges basement towards the WNW. The basal contact of the Helvetic nappes, which we call the Helvetic Basal thrust (HBT), often corresponds to a décollement level localized above the Triassic unconformity, but that locally also affects the basement. We suggest that most of the subalpine ranges are klippes above the HBT, and estimate the shortening of the thrust from previously published cross-sections to be between 13 and 32 km. According to published ages, we argue that the HBT was active in the Oligo-Miocene, between ∼30 and ∼14 Ma. After ∼14 Ma and until ∼6 Ma, the HBT is offset by late steep out-of-sequence faults, including back-thrusts and the Mont-Blanc shear zone that was previously a ramp of the HBT. The transition of the major thrust system from the HBT rooting above (east) of the Mont-Blanc to the Alpine sole thrust rooting below (west) of the Aiguilles Rouges occurred between 18 and 14 Ma. • Structural analysis and 3D mapping of the Aiguilles Rouges and Chamonix zone. • Thrust of the Mesozoic sedimentary cover ∼30 km WNW at 30–14 Ma. • Steep thrusts in the Miocene (14–6 Ma). • 15 Ma long Helvetic thrusting has been overlooked in alpine orogeny models. [ABSTRACT FROM AUTHOR]

For many tectonicists, the structural development of the northern Tibetan Plateau stops at the Altyn Tagh Fault (ATF). This study challenges that assumption. Structural field observations and remote sensing analysis indicate that the Sanweishan and Nanjieshan basement cored ridges of the Archean Dunhuang Block, which interrupt the north Tibetan foreland directly north of the ATF, are bound and cut by an array of strike-slip, thrust and oblique-slip faults that have been active in the Quaternary and remain potentially active. The Sanweishan is a SE-tilted block that is bound on its NW margin by a steep south-dipping thrust fault that has also accommodated sinistral strike-slip displacements. The Nanjieshan consists of parallel, but offset basement ridges that record NNW and SSE thrust displacements and sinistral strike-slip. Regional folds characterize the extreme eastern Nanjieshan and appear to have formed above blind thrust faults which break the surface further west. Previously published magnetotelluric data suggest that the major faults of the Sanweishan and Nanjieshan ultimately root to the south within conductive zones that are inferred to merge into the ATF. Therefore, although the southern margin of the Dunhuang Block focuses significant deformation along the ATF, the adjacent cratonic basement to the north is also affected. Collectively, the ATF and structurally linked Sanweishan and Nanjieshan fault array represent a regional asymmetric half-flower structure that is dominated by non-strain partitioned sinistral transpression. The NW-trending Dengdengshan thrust fault system near Yumen City appears to define the northeastern limit of the Sanweishan-Nanjieshan block, which may be regionally viewed as the most northern, but early-stage expression of Tibetan Plateau growth into a slowly deforming, mechanically stiff Archean craton. [ABSTRACT FROM AUTHOR]

En este artículo se discute el origen y mantenimiento de la biodiversidad en las montañas tropicales, con énfasis en el Neotrópico, y se concluye que los patrones de biodiversidad de las biotas de gran altura no pueden ser explicados sin la acción combinada de la tectónica neógena y los cambios climáticos del Pleistoceno.

Составлен профиль МСЗ в Осетинском секторе Большого Кавказа. Получена информация о глубинном строении складчатого сооружения. По результатам геолого-геофизического изучения сделаны заключения о глубинном строении Большого Кавказа.

The article discusses the impact that climatic changes during the mid-Pleistocene period had on the loss of net mass from the St. Elias Mountains in Alaska, including its impact on plate tectonics and erosion. An overview of the role that climate changes played in the erosion of sediments of St. Elias Mountains is provided. The relationship between the expansion of glaciers and erosion is discussed.

The Eurekan Orogeny, which created much of the high topography of Ellesmere Island and adjacent Greenland, exhibits a crustal architecture linked to intraplate orogenesis in the Cenozoic. It is generally considered that the rotation of Greenland in the Eocene (related to sedimentary basin formation in Baffin Bay) produced compressional intraplate tectonics. Deformation in the region is notably localized to the Central Ellesmere Domain and the Northern Ellesmere Domain. However, an important tectonic feature of Ellesmere Island is the Hazen Stable Block, which shows horizontal Paleogene Eureka Sound group strata overlying Palaeozoic-age steeply dipping beds. The intense deformation in the Hazen Stable Block is related to continental orogenesis in the Late Silurian–Devonian. Therefore, the Hazen Stable Block is thought to have undergone only minor Eurekan-age (55–35 Ma) deformation, while surrounding (highly deformed) units may have re-activated faults from Paleocene continental amalgamation. Here, high-resolution thermal–mechanical numerical experiments are implemented to explore lithospheric deformation (related to continental shortening) for a range of tectonic scenarios, namely, the presence of inherent deformational “scars” and rheologically strengthened crust/mantle lithosphere (both due to ancient continental accretion). This study marks the first geodynamic excursion to this high Arctic region, and we present some of the first interpretations of the development of Eurekan-age lithospheric evolution. Our results show that a rheologically strong Hazen Stable Block crust produces tectonics similar to the Eurekan Orogeny. Furthermore, lithospheric scars can generate more localized deformation and topography than rheological changes to the lithosphere and may offer a new interpretation on enigmatic intraplate tectonics. [ABSTRACT FROM AUTHOR]

The observation that sediment flux from mountain ranges struck by high magnitude earthquakes can be strongly influenced by coseismic mass movements brings into question the nature of coseismic deformation as a net contributor to mountain building. To better constrain the role of high-magnitude earthquakes in orogenesis, high-resolution data of earthquake induced mass wasting is required for areas of differing tectonic, morphological, and climatic settings. Here we compare the erosional flux to the tectonic flux associated with the 2010 M w = 7.2 Sierra El Mayor earthquake in Mexico and examine the landslide patterning of coseismic mass movements associated with this event. The ruptured fault system has a significant strike-slip component with subsidence along the eastern flank and uplift on the western flank of the range. Peak ground acceleration was highest along the steepest sections of the range such that the frequency of landslide occurrence was strongly correlated to slope gradient. Both vertical and horizontal coseismic displacement demonstrated a strong control over landslide initiation. This result suggests that strike-slip systems experience very different landslide patterning to thrust faults during earthquakes. Based on interferometric analysis of synthetic aperture radar images, the earthquake resulted in a total uplifted volume of 41.6 × 10 6 m 3 and a loss of 95.2 × 10 6 m 3 due to subsidence. This suggests a net tectonic volumetric flux of − 53.6 × 10 6 m 3 . Sediment mobilisation by coseismic landslides is estimated at − 2.7 × 10 6 m 3 derived from a manually mapped inventory using SPOT 5 multispectral imagery. Thus, the net volume loss through coseismic subsidence of the mountain range generated a strongly negative mass flux, which was only marginally enhanced by mass wasting. [ABSTRACT FROM AUTHOR]

A succession of 5 FIA trends (foliation intersection or inflection axes in porphyroblasts) preserved in high temperature-low pressure regime PreCambrian rocks in the Texas Creek, Arkansas River region reflected by the fold axial plane traces and schistosity data in this region. Similar fold axial plane trace data measured in Palaeozoic rocks in Chester Dome, Vermont, which is high temperature to medium pressure regime, only preserve the effects of the youngest FIAs of the all 5 FIA sets that obtained in this region. The other three FIA sets have no equivalent fold axial planes. This difference from shallow to deeper orogenic regimes reflects decreasing competency at greater pressure with collapse and unfolding of earlier formed folds. The greater overlying load of rocks has tended to flatten all but the very largest early-formed structures, preserving only those folds that were more recently developed. [ABSTRACT FROM AUTHOR]

The assembly and dispersion of continental crust are first-order controls on paleogeography and geochemical cycles. The associated reworking of Earth's crust can be tracked with zircon initial hafnium (ε Hf T) through space and time. Here we apply a new method of quantitative analysis using ε Hf T density estimates based on a compilation of 155,329 ε Hf T values. Investigation of the global database reveals significant geographic and temporal bias in the ε Hf T record associated with sampling and regional tectonic events. Recent research has attempted to address global ε Hf T bias using resampling methods to augment gaps of low ε Hf T data density, which in turn obfuscates tectonic signals and artificially weights outliers. Instead, we evaluate ε Hf T density patterns for both igneous and detrital zircon on eight continental zones demarcated by Paleozoic sutures: Africa, Antarctica, Asia, Australia, Baltica, North America, Peri-Gondwana, and South America. Pairwise two-dimensional quantitative comparison highlights similarity in timing and ε Hf T values between zones, all of which can be linked to documented shared regional tectonism. Integration of all pairwise comparisons reveals that peak similarity corresponds to the timing of supercontinent amalgamation, and that the associated ε Hf T differs depending on the style of supercontinent amalgamation, particularly internal versus external orogenesis. The three most recent supercontinents produced distinctive ε Hf T signals, shared by the constituent continental zones. The supercontinents Rodinia and Pangea were constructed through collisions of marginal arc terranes, peripheral to ancient crust, and did not produce highly enriched ε Hf T values. In contrast, Ediacaran to Cambrian formation of the Gondwana supercontinent was largely the product of internal Pan-African orogens that formed directly after Neoproterozoic Rodinia rifting and arc accretion forming the Arabian Shield. The final assembly of Gondwana was dominated by continent-continent collisions of old radiogenic crust without establishment and accretion of extensive intervening depleted arc terranes, resulting in a more enriched distribution of ε Hf T values compared to prior and subsequent supercontinent formation. The secular ε Hf T record is the product of spatiotemporally biased sampling and preservation of specific orogenic belts with predictable ε Hf T data arrays, modulated by the amalgamation, tenure, and breakup of supercontinents through time. • Zircon Hf is predictable based on tectonic context. • Global Hf records are geographically and temporally biased. • All major Hf excursions can be linked to regional orogenic events. • Zircon Hf is modulated by the amalgamation, tenure, and breakup of supercontinents. [ABSTRACT FROM AUTHOR]

Abstract: New SHRIMP U/Pb zircon ages of 472.2±5.8Ma and 471.2±5.9Ma are presented for the age of peak metamorphism of Barrovian migmatites. 40Ar/39Ar ages for white mica from the Barrovian metamorphic series are presented, and are recalculated using recently-proposed revisions to the 40K decay constants to allow more precise and accurate comparison with U/Pb ages. The 40Ar/39Ar ages are found to vary systematically with increasing metamorphic grade, between c. 465Ma for the biotite zone and c. 461Ma for the sillimanite zone. There is no evidence for any significant metamorphic heating during the first 15Myr of the Grampian Orogeny (before c. 473Ma) or the final 4Myr (after c. 465Ma). The Barrovian metamorphism occurred over a period of ~8Myr within the ~27-Myr Grampian Orogeny. The Barrovian metamorphism records punctuated heating, was temporally and spatially associated with large-scale bimodal magmatism, and developed within crust that was not overthickened. The temporally distinct nature of the Barrovian metamorphic episode within the Grampian Orogeny, and its heating pattern and tectonic context, are not consistent with significant heat contribution from thermal equilibration of overthickened crust. Rather, the Barrovian metamorphism records a transient phase of crustal thermal disequilibrium during the Grampian Orogeny. Temporal and spatial association with Grampian bimodal magmatism is consistent with production of the Barrovian metamorphic series within the middle crust as the result of advection of heat from the lower crust and/or mantle. The Barrovian metamorphic series – the classic example of ‘orogenic regional metamorphism’ – did not form in response to crustal thickening and thermal relaxation, but appears to record large-scale contact metamorphism. [Copyright &y& Elsevier]

We present a tectonic map of the Tauern Window and surrounding units (Eastern Alps, Austria), combined with a series of crustal-scale cross-sections parallel and perpendicular to the Alpine orogen. This compilation, largely based on literature data and completed by own investigations, reveals that the present-day structure of the Tauern Window is primarily characterized by a crustal-scale duplex, the Venediger Duplex (Venediger Nappe system), formed during the Oligocene, and overprinted by doming and lateral extrusion during the Miocene. This severe Miocene overprint was most probably triggered by the indentation of the Southalpine Units east of the Giudicarie Belt, initiating at 23-21 Ma and linked to a lithosphere-scale reorganization of the geometry of mantle slabs. A kinematic reconstruction shows that accretion of European lithosphere and oceanic domains to the Adriatic (Austroalpine) upper plate, accompanied by high-pressure overprint of some of the units of the Tauern Window, has a long history, starting in Turonian time (around 90 Ma) and culminating in Lutetian to Bartonian time (45-37 Ma). [ABSTRACT FROM AUTHOR]

Abstract: The surface expression of a lateral polarity change of continental mantle lithosphere subduction has been studied by using lithosphere-scale physical models. Key parameters investigated were: the degree of lateral coupling between adjacent domains of opposing subduction polarity, the width of the zone separating the domains, and the lithosphere geometry and rheology. The model results illustrate an asymmetric lithospheric structure induced by deformation of the downgoing plates, which have been separated by a narrow transition zone. A wide and symmetric orogenic wedge overlying a region of thickened mantle lithosphere and hampered subduction characterizes this transition zone. In addition, interaction between the neighboring subduction domains caused downbending of the upper plates and resulted in the lateral termination of crustal structures and lowering of surface topography. The lateral extent of interaction between the domains strongly depends on the degree of coupling between the domains, the rheology of the mantle lithosphere and the amount of bulk shortening. The modelling results have major implications on the interpretation of seismic and tomographic data from the European Alps in terms of the crust and lithosphere geometries. It appears that an observed lateral change of subduction polarity at mantle depth can explain the variations of wedge build-up between the Western/Central and Eastern Alps. [Copyright &y& Elsevier]