Intracontinental Orogen Research Articles

Lithospheric resistivity structure of the Xuefeng Orogenic Belt and its implications for intracontinental deformation in South China

The Xuefeng Orogenic Belt (XFOB), located in the central part of the South China Block, is a typical Mesozoic intracontinental orogen in the central Jiangnan Orogenic Belt. By collecting magnetotelluric (MT) data across the XFOB, we obtained the resistivity structure of the lithosphere, which sheds light on the Mesozoic intracontinental orogenic processes in the XFOB. The resistivity structure reveals a low-resistivity body (<10 Ω∙m), beneath the XFOB, dipping southeast wards from a depth of 10 km to the bottom of the crust. This conductor is interpreted as a relic of the lower detachment zone, which coincides with low-density areas obtained from joint inversion of seismic models. It is believed to result from mineral fluids migrating along the thrust fault and squeezing sulfides into folds. Four low-resistivity bodies were identified at three extensional locations along the Jiangshan-Shaoxing Fault and at the Cili-Baojing Fault. The low-resistivity body (<10 Ω∙m) at the junction of the Shaoyang and the Hengyang Basin is located at the point where the Moho depth thins. The variation trend of the terrestrial heat flow values, with this low-resistivity body as the plate boundary, is consistent with the average variation of the terrestrial heat flow values within the block. We propose that the low-resistivity body under the Qidong-Yongzhou-Guilin fault conforms to the characteristics of the suture zone in the resistivity structure. Its existence indicates that the missing location of the Jiangshan-Shaoxing suture zone of the Yangtze and Cathaysia Block in the middle-southwest section of the South China Block is the Qidong-Yongzhou-Guilin fault. The Yangtze Block and the Hengyang Basin show high resistivity, the depth of which reaches 100 km and 40 km, respectively. Based on the resistivity model and geological data, the XFOB experienced Triassic compression, leading to basement decollement, thrusting, and nappe structures due to low-angle Paleo-Pacific Plate subduction. This compression also led to the uplift of the orogenic belt. Moreover, under the tension caused by the high-angle retreat of the Paleo-Pacific Plate, the Cretaceous extensional tectonics led to detachment along the thrust faults, forming half-graben and basin structures along the margins.

Lithospheric Folding Controls the Intracontinental Orogen of South China: Insight from Numerical Simulation

Abstract Orogenic processes worldwide have been attributed to various deformation mechanisms. However, the significance of lithospheric folding in these processes has often been overlooked and underestimated. Within the South China Block (SCB), a region marked by notable temporal and spatial variability in intracontinental deformation, the emergence of fold-and-thrust belts during the Paleozoic and Mesozoic periods has captured a scientific interest. The mechanisms governing the genesis of these belts remain a subject of debate, with no discernible subduction interface accounting for the extensive-scale fold-thrust deformation. Moreover, the SCB presents a substantial variation in lithospheric thickness, exceeding 100 km, offering a plausible mechanism for lithospheric folding. To interrogate this mechanism, we conducted lithospheric compression simulations via two-dimensional finite element methods, incorporating variable viscosity both laterally and vertically within the SCB. Our models elucidate that disparities in lithospheric strength beget distinctive deformational manifestation within the SCB. We observe that a weaker lithosphere tends to uplift, whereas a stronger lithosphere tends to subside during compression. Lithospheric strength also influences the Xuefengshan uplift and the spatial distribution of deformational features. In addition, lithospheric folding can account for crustal shortening and the presence of deep anomaly structures. A compelling correlation emerges between lithospheric folding and fluctuations in Moho depth and lithospheric thickness, suggesting its potential influence over the prolonged topographical evolution and shifts in depositional environments within the SCB. This study sheds new light on the role of lithospheric folding in the complex geodynamic history of the SCB and highlights its importance in understanding the broader context of orogenic processes worldwide.

The major Adassil-Medinet fault; a complex evolution of high angle transpressive Variscan shear zones (Western High Atlas, Morocco)

The Western High Atlas is one of the most important sectors of the Variscan foldbelt in Morocco and also of its Alpine intracontinental orogen. Its tectonic evolution is thus essential for the understanding, not only of the Moroccan geology, but also of the interaction between successive orogenic cycles which is one of the focus of this article. Furthermore, as the Moroccan Variscides must be seen in the context of the complex dextral collision between Laurasia and Gondwana, this is also a contribution to the comprehension of the complexity of transpressive regimes and strain partitioning processes.New data show that WNW-ESE sinistral Variscan shear zones (mainly the Addouz-Adassil-Anamrou one - AAAsz), although secondary to the main orogenic scale ENE-WSW dextral shear zones, must be considered in order to understand the Late Paleozoic deformation and its Alpine reactivation. In fact, the concentration of the last stages of the Variscan ductile deformation in the steep and irregular AAAsz played an important role in the initiation and localisation of the minor magmatic events and influenced the geometry and kinematics of the Late Variscan WNW-ESE sinistral shear zones. Furthermore, during the Alpine inversion, the orientation of the AAAsz and related major anisotropies tend to be reactivated, with a major reverse component, giving rise to the irregular Adassil-Medinet fault zone, one of the most important structures of the Western High Atlas.

Intraplate thrust orogeny of the Altai Mountains revealed by deep seismic reflection

The Altai orogen is a typical intracontinental orogen in Central Asia that experienced far-field deformation associated with Indian-Eurasian plate convergence. This region is characterized by uplift comparable to that of the Tianshan Mountains but has a distinct strain rate. Half of the Indo-Asia strain is accommodated by the Tianshan Mountains, whereas the Altai Mountains accommodates only 10%. To elucidate how the Altai Mountains produced such a large amount of uplift with only one-fifth of the strain rate of the Tianshan Mountains, we constructed a detailed crustal image of the Altai Mountains based on a new 166.8-km deep seismic reflection profile. The prestack migration images reveal an antiform within the Erqis crust, an ∼10 km Moho offset between the Altai arc and the East Junggar area, and a major south-dipping (30° dip) thrust in the lower crust beneath the Altai Mountains, which is connected to the Moho offset. The south-dipping thrust not only records the southward subduction of the Ob-Zaisan Ocean in the Paleozoic but also controlled the Altai deformation pattern in the Cenozoic with the Erqis antiform. The Erqis antiform prevented the extension of deformation to the Junggar crust. The south-dipping thrust in the lower crust of the Altai area caused extrusion of the lower crust, generating uplift at the surface, thickening of the crust, and steep (∼10 km) Moho deepening in the Altai Mountains. This process significantly widened the deformation zone of the Altai Mountains. These findings provide a new geodynamic model for describing how inherited crustal structure controls intraplate deformation without strong horizontal stress.

Cenozoic sedimentary evolution of the Tiereke section on the northern Tarim Basin: implications for the intracontinental mountain building of the Eastern Tian Shan

The Tian Shan is one of the world's largest intracontinental orogens and provides an excellent example for deciphering the intracontinental responses to the tectonics of plate boundaries. Despite its significance, the timing and driving mechanism of the Cenozoic mountain building of the Tian Shan in the context of the India–Eurasia collision remain controversial. In this study, Cenozoic stratigraphy of the Tiereke section along the western Kuqa Depression of the northern Tarim Basin on the south foreland of Eastern Tian Shan (east of 80°E) has been investigated. The results indicate that the Cenozoic deposition of the Tiereke region sequentially experienced a transgression from the Kumugeliemu Group to the Suweiyi Formation and a regression from the Suweiyi to the Kuqa Formations. Based on the contact relationships and conglomerate textures, three stages of high-energy alluvial deposition have been identified in the lower Kumugeliemu Group, upper Jidike and Kangcun–Kuqa Formations, respectively. These sedimentary events were interpreted to represent phases of Eastern Tian Shan mountain building at c. 54 Ma, c. 27 Ma and since c. 9.7 Ma according to previous magnetostratigraphic results, which were possibly related to the initial India–Eurasia collision, the collision between the India and Tarim lithospheric mantles, and the basinward propagation of deformation, respectively. Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

Extent and significance of the Racklan–Forward Orogen in Canada: far-field interior reactivation during Nuna assembly

Abstract Mesoproterozoic orogenesis is well established on the western and southern flanks of Laurentia in the well-known Racklan–Forward and Mazatzal orogens, but its significance within the previously assembled interior of the supercontinent Nuna has not been established. We examine regional isotopic and structural evidence for Mesoproterozoic deformation in the c. 1.7–1.63 Ga Hornby Bay, Elu, Thelon and Athabasca intracontinental basins, and present evidence for Mesoproterozoic reactivation of Paleoproterozoic structures in the Wopmay and Trans-Hudson orogens. The Racklan–Forward Orogeny in the interior of north Laurentia comprises north–south-trending, high-angle, east-vergent folds and thrusts that occur across a region 1660 km wide and over 1000 km long, stretching from the Yukon to near Hudson Bay and from Banks Island to below the Western Canada Sedimentary Basin. The structures progress from ductile amphibolite and greenschist facies in the Racklan type area to sub-greenschist facies and ultimately brittle or brittle-ductile in the far foreland, showing a predominant thick-skinned style typical of many intracontinental orogens. We present compiled low-temperature thermochronological data, including ages of spatially associated uraninite mineralization, to characterize the scope of reactivation of basement structures in the Archean Rae craton in Nuna's interior. We compare the nature of widespread far-field reactivation in the Racklan–Forward Orogen with other orogens of Nuna's assembly to show it is unusual for Nuna's peripheral margin. We suggest that c. 1.6 Ga continent–continent collision of North Australia with NW Laurentia propagated stresses far into the interior as a result of combined favourable pre-existing structural grain and a weak subcontinental lithospheric mantle in the Rae craton due to repeated episodes of refertilization across 500 Ma of accretion and intrusion. Cratons that experience the complex, two-sided collision and protracted upper plate setting during supercontinent assembly noted herein may be particularly susceptible to extensive foreland propagation of peripheral orogens.

The Joining of North and South China During the Permian: Coherent Metamorphic Evidence From East Asia Orogenesis

AbstractThe joining of the North and South China blocks marks the formation of the united East Asian continent, which is an integral part of Pangea. The amalgamation of these two continental blocks also resulted in the formation of the world‐class ultrahigh pressure orogenic belt, namely the Dabie–Sulu orogenic belt. Figuring out the time of the initial collision between the two continents is critical for resolving questions such as the duration and the geodynamic processes of the orogeny. A Triassic joining time has been suggested by the geochronology of the eclogite facies rocks in this orogenic belt. However, paleomagnetic and paleontological studies suggested a Permian docking time for these continental blocks. In this paper, we present new metamorphic ages of rocks from northern Dabie and the Permo–Triassic intracontinental orogen of South China, which are all closely associated with this continental collisional event. New age dating results, as well as a synthesis of recent studies on metamorphic rocks occurring in southeastern North China and the Cathaysia Block of South China, show that the onset of the collisional orogenesis along the eastern part of the orogenic belt dates back to the Middle Permian (270–252 Ma). Considering these data and other geological records, we provide a new tectonic model for the major continents of East Asia, in which we show that the initial collision between North and South China occurred in the east during the Middle Permian, and then propagated westward. Continental collisions forming mountains and closing seaways in East Asia thus apparently occurred before the end‐Permian mass extinction, suggesting these paleogeographic changes might have also preconditioned and facilitated the end‐Permian biospheric crisis in the region.

Differential fold interference patterns in an intracontinental orogen: Insights from superposed buckle folding in southern Jiangxi Province, South China Block

The South China Block (SCB) experienced multi-stage tectono-magmatic events during the Mesozoic, forming a broad and episodic intracontinental orogenic belt. It is controversial whether the driving force of the Mesozoic intracontinental orogeny in the SCB is related to the far-field effects of plate convergence. To better understand the driving mechanism of intracontinental orogeny, we conducted a detailed structural investigation of the Xingguo area in southern Jiangxi Province, located in the central part of the SCB. Two regional-scale buckling superposed folds were identified as the Chayuan arcuate syncline of the fold axis protruding to the north (Type 2a interference pattern) and the Xiefang syncline of the fold axis extending NW–SE (Type 1d interference pattern). Although there are differences in fold interference patterns, the Chayuan arcuate syncline and Xiefang syncline were formed by the superimposition of the Middle–Late Triassic NE–SW shortening and the Middle–Late Jurassic nearly E–W shortening. This phenomenon of the differential fold interference patterns in the same tectonic setting is determined by the difference in geometric characteristics of their initial folds. Combined with the variation of the Mesozoic paleostress field, it is considered that the Mesozoic intracontinental orogeny in the SCB is mainly controlled by the far-field stress propagation generated by plate interactions. Based on the analysis of tectonic architecture, we propose that the Mesozoic tectonic evolution of the SCB experienced a transformation from multi-plate convergence in the Triassic to Andean-type subduction in the Jurassic. This tectonic transformation finally resulted in the reactivation of the Precambrian multi-terrane collage of the SCB.

How do pre-existing weak zones and rheological layering of the continental lithosphere influence the development and evolution of intra-continental subduction?

• The depth of a preexisting weak zone is one of the key factors in initiating intra-continental subduction. • Crustal internal friction angle plays an important role in altering the deformation type of a continental collision system. • The reactivation of the suture may be an auxiliary condition for the evolution of the south-dipping continental subduction underneath the North Pamir. Intra-continental subduction is of special importance for studying the formation of intra-continental orogens, crust-mantle structural evolution, and the far-field effects of continental collision, whose mechanism is still a matter of discussion. In this work, we investigated the role of pre-existing weak zones and the continental lithospheric rheological layering in the formation and evolution of the intra-continental subduction based on a 2D finite element numerical technique. The model results indicate that the deeper the intra-continental weak zone is and the faster the convergence velocity is, the more likely it is to develop into a new intra-continental subduction. Altering the rheological strength of the overriding plate may not have a substantial impact on the intra-continental subduction mode when the depth of the pre-existing weak zone is larger than half of the lithospheric thickness. In contrast, the lithospheric rheological strength is closely related to the continental collision system’s deformation style: Models with a weaker overriding plate are inclined to delaminate continuously under collision, whereas a strong overriding plate results in the subducting plate’s roll-back. The reactivation of the suture that runs deep into the lithosphere as a result of the Indian-Asian continental collision could be one of the crucial factors controlling the formation of the south-dipping subduction under the North Pamir.

Hydrothermal rutile U-Pb dating of gold mineralization in the Jiangnan Orogen: A case study of the Hengjiangchong gold deposit in northeastern Hunan

The Jiangnan Orogen is a well-known gold belt in China with a large number of gold deposits. The Jiangnan Orogen has complex geological history, and most gold deposits have not been well dated. Consequently, the regional timing of gold mineralization is still controversial. The Hengjiangchong is a representative gold deposit in the orogen. In this study, syn-ore hydrothermal rutile in quartz-polymetallic sulfides-gold-calcite veins was dated by LA-ICP-MS, yielding a Tera-Wasserburg lower intercept U-Pb date of 416.1 ± 7.3 Ma (2σ, n = 26, MSWD = 2.4). This date represents the age of gold mineralization at Hengjiangchong, and falls within the generally accepted timing of gold mineralization in the Jiangnan Orogen (ca. 425–400 Ma). Combined with the regional kinematics, gold mineralization likely occurred during the extension associated with the Yangtze-Cathaysia post-collisional deformation in the Siluro-Devonian intracontinental orogen. This also indicates that the late Silurian was a major gold mineralization epoch in the Jiangnan Orogen, challenging to some previous claims that late Silurian hydrothermal veins are largely ore barren.

Intracontinental deformation of the Tianshan Orogen in response to India-Asia collision

How the continental lithosphere deforms far away from plate boundaries has been long debated. The Tianshan is a type-example of ongoing lithospheric deformation in an intracontinental setting. It formed during the Paleozoic accretion of the Altaids and was rejuvenated in the Cenozoic, which might be a far-field response to the India-Asia collision. Here we present seismic images of the lithosphere across the central Tianshan, which were constructed from receiver functions and Rayleigh wave dispersions along a N–S-trending linear seismic array. We observe an extensively deformed lithosphere in the Tianshan with inherited, structurally controlled brittle deformation in the shallow crust and plastic deformation near the Moho. We find that earlier multiple accretionary structures were preserved in the crust, which was deformed by pure-shear shortening in the south and thick-skinned tectonics in the north but was limitedly underthrusted by surrounding blocks. A balanced cross-section of Moho discontinuities supports the concept that intracontinental deformation in the Tianshan intensified synchronously with the direct contact between the underthrusting Indian slab and the Tarim Craton in the Late Miocene (~10 Ma). These findings provide a robust and unified seismic model for the Tianshan Orogen, and confirm that effective delivery of the India-Asia collision stress induced the rejuvenation of this intracontinental orogen.

Formation of an Intracontinental Orogen Above the Permo-Triassic Mantle Convection Cell in the Paleo-Tethys Tectonic Realm due to Far-Field Stress Derived From Continental Margins

The identification of intraplate orogens seemingly poses challenges to the plate tectonic theory. Delineating the formation processes of intraplate orogens can provide clues for the better understandings of the above issue. Although still controversial, the Indosinian (Permo-Triassic) orogeny in the South China Block (SCB) is potentially a good example of intracontinental orogen. In this paper, we carry out studies on the Indosinian high-grade rocks in the northeastern Cathaysia Block of the SCB, hoping to cast light on the features and formation processes of intraplate orogenic belts. These rocks exhibit HP/HT granulite facies mineral assemblages and reaction textures imply that they witnessed eclogite-facies metamorphism. Their clockwise P-T trajectories with isothermal decompression stages suggest significant crustal thickening followed by quick orogenic collapse. Immobile whole-rock trace elements indicate basaltic protoliths features, resembling E-MORB and OIB, respectively. SIMS zircon U-Pb age dating confirms Indosinian metamorphic ages of ∼248 Ma and a protolith age of ∼953 Ma. The mantle-like O isotopic compositions of the Neoproterozoic magmatic zircon cores further attest that they were primarily mantle derived rocks. The whole-rock Sm-Nd isotopic compositions show more enriched features because of metamorphic alteration, while zircon Lu-Hf isotopic results show primitive characteristics with Neoproterozoic model ages. These features suggest that the high-grade mafic rocks, as well as the metamorphosed early Precambrian metasedimentary rocks hosting them, are all continental crust components and juvenile oceanic crust components featuring plate margins are absent during the SCB Indosinian orogeny. Characteristics of these high-grade rocks and their spatial occurrences are both consistent with the proposal of an intracontinental orogen. After summarizations and comparisons of the Indosinian plate margin activities around the SCB, we suggest that this northeast-southwest trending orogenic belt is geometrically consistent with two mantle convection cells, with one conveying the SCB northward to collide with the North China Craton, and the other conveying the Paleo-Pacific plate northwestwards to form an active continental margin along the southeast SCB. The driving mechanism of the formation of the SCB Indosinian intracontinental orogenic belt could have broad implications for other intraplate orogens around the world.

Seismic anisotropy in the central Tien Shan unveils rheology-controlled deformation during intracontinental orogenesis

AbstractThe initiation and evolution of compressional intracontinental orogens are favored by rheologically weak lithosphere underneath; however, how this weakened lithosphere responds to the regional stress regime remains vigorously debated. The Tien Shan mountains in central Asia provide the best example to illustrate the deep deformational responses to intracontinental orogenesis. We present new constraints on the nature of seismic anisotropy in the crust and upper mantle of the central Tien Shan through shear-wave splitting analyses. Our results reveal a sharp change in the orientations of crustal anisotropic fabrics on two sides of the mountains. The convergence-parallel fast orientations in the northern segment are closely related to the lower-crustal simple-shear deformation caused by the underthrusting of the Kazakh Shield, whereas the depth-independent orogen-parallel fast orientations in the southern segment suggest vertically coherent pure-shear thickening of the Tien Shan lithosphere in response to the northward indentation of the Tarim Basin. The thickened lithosphere has partly foundered into the deep mantle, contributing to the accelerated shortening deformation in the late Cenozoic. Our observations demonstrate the complex tectonic processes in the Tien Shan and suggest that the rheological properties of bounding blocks can play a significant role in shaping the lithospheric structures of intracontinental orogens.

The deep structure of the Salair fold-cover structure according to magnetotelluric studies

The results of magnetotelluric studies (MTS) performed within the Salair cover-folded structure on two profiles are considered: the Zabrodino village – the Rodnikovy village (1) and the Smaznevo village – the Kotino village (2). The profiles are oriented crosswise along the main structures and intersect Salair and the western part of the Kuznetskiy trough. The analysis of the obtained data showed that a subhorizontal underlying conducting zone is distinguished in the Earth’s crust of the Salair fold-cover structure, such zone is typical for intracontinental orogens. The zone is considered as a deep separation failure. The nature of the electrical resistance values distribution confirms the presence of the Salair thrust on the Kuznetskiy deflection. The Alambay ophiolite zone on the geoelectric section corresponds to a highly gradient region, indicating the suture zone of this structure. High resistivity values in the northern part of the Khmelevskoy trough are associated with the widespread development of granitoid massifs that are not covered by erosion.

Preface

VIII International Symposium “PROBLEMS OF GEODYNAMICS AND GEOECOLOGY OF INTRACONTINENTAL OROGENS” (June, 28 – July, 2, 2021; Bishkek, Kyrgyz Republic; online regime via Zoom due to the restrictions associated with the COVID-19 pandemic) was held within the framework of the Year of Science and Technology in Russia and was dedicated to 85th birthday anniversary of Yuri Trapeznikov – the founder and the first director of the Research Station of the Russian Academy of Sciences in Bishkek city (RS RAS). The Symposium became a representative international scientific event held on the basis of the RS RAS and the International Research Center - Geodynamic Proving Ground in Bishkek (IRC-GPG). More than 100 scientists and specialists from seven countries (Russia, Kyrgyzstan, Kazakhstan, Uzbekistan, Tajikistan, Ukraine and Japan) took part in the Symposium with online reports.The basic themes of the Symposium were quite diverse and related to the main directions of fundamental research in the area of Earth sciences:• Deep structure and evolution of the Earth’s crust and upper mantle in the light of modern conceptions of Geodynamics. Instrumental methods of studying of intracontinental orogens lithosphere: heterogeneities, physical nature of boundaries.• Stressed and deformed state of the Earth’s crust, problems of its block structure and selfsimilarity of geodeformation processes. Seismotectonics of intracontinental orogens zones.• Complex monitoring of seismically active zones. Problems of geospheres interaction, including the influence of physical fields on endogenous processes.• Electromagnetic methods in studying of seismically active regions and in monitoring of geodynamic processes. Development of inversion methods of electromagnetic data.• Assessment of seismic risk, regional studies of seismic regime.• Environmental and social consequences of endogenous and exogenous geological processes, prediction of hazardous events (earthquakes, landslides, etc.). Each of the mentioned themes was considered separately during special section.There were about 30 young researchers who took part in the Symposium – this participation allowed them to become involved in the modern scientific achievements in the Earth sciences area, as well as to receive the leading specialists consultations needed for the successful further research activity.The Symposium states that such meetings and forms of scientific and human communication are very useful and contribute to increase the general level and developing various areas of research in the field of Earth sciences.List of ORGANIZING COMMITTEE, Photo, Logos are available in this pdf.

Pressure–temperature–time constraints on gneiss dome formation in an intracontinental orogen

AbstractThe Entia Gneiss Complex represents the mid‐crustal core of the intracontinental Alice Springs Orogen. Located in the Harts Range, central Australia, it is characterized by the development of a domal structure including two sub‐domes separated by a steeply dipping median high‐strain zone. Dominantly, orthogneiss basement crops out through a structurally overlying cover sequence represented by the Harts Range Group and records evidence of hydration, recrystallization, and partial melting of precursor Paleoproterozoic granulite facies assemblages at amphibolite facies conditions. The structurally lowest parts of the Harts Range Group were metamorphosed to peak conditions of 10.5 kbar and ~880°C during rift‐related magmatism at 480–460 Ma, immediately prior to the onset of the Alice Springs Orogeny at 450–300 Ma. By contrast, the underlying Entia Gneiss Complex records widespread metamorphism and wet melting at upper amphibolite facies conditions. Phase equilibrium modelling and in situ LA–ICP–MS geochronology of rare, low‐variance kyanite–garnet‐bearing metapelites indicate that maximum P–T conditions of ~9 kbar and ~680°C were reached between c. 360–330 Ma, demonstrating a distinctive metamorphic and temporal evolution relative to the overlying Harts Range Group that can be linked to rheological stratification. Based on the integration of our results with existing monazite, zircon, and titanite geochronology, we interpret doming of the Entia Gneiss Complex to have involved compressive ascent of rheologically weakened crust below a region of extending upper crust near the termination of the Alice Springs Orogeny. In this way, the Harts Range Group represents a cooled, locally extending thrust sheet over ductile basement quasi‐concurrent with doming. Texturally‐late sillimanite combined with increasing Y content in monazite indicates high‐temperature, kyanite‐grade metamorphism was closely followed by decompression (3–4 kbar drop from peak conditions) and rapid cooling below 600°C during emplacement of the Entia Gneiss Complex at shallower crustal levels. The findings of this study highlight the feedback between hydration, retrogression, rheological weakening, and strain accommodation, thus allowing better evaluation of the thermomechanical history of gneiss dome formation within a narrow (&lt;80 km wide) preconditioned intracontinental corridor.Highlights First modern P–T–t framework for gneiss dome formation in the Entia Gneiss Complex, central Australia. The onset of metamorphism, partial melting and ductile flow at c. 360 Ma was catalysed by hydration of granulite facies basement during rift inversion. Rapid exhumation of partially molten crust from depths of &gt;20 km is marked by fluid‐mediated resetting of monazite down to c. 310 Ma. Rheological stratification enabled and accelerated exhumation of the highest‐grade corridor of a narrow intracontinental orogen.

STRUCTURAL-PHOTOMETRIC IMAGES AS REFLECTION OF THE TIEN SHAN INTEGRAL TECTONIC SEGMENTATION

The article discusses (first) the possibility of the structural-photometric images application for the Tian Shan intracontinental orogen segmentation. With the help of the Photoshop Pro program, the geological map into a system of graphic images was transformed. This technique allowed to identify the integral structural and morphological heterogeneity of the Kyrgyz Tian Shan upper crust and to create a scheme of the region's morphostructural segmentation.

An intracontinental orogen exhumed by basement-slice imbrication in the Longmenshan Thrust Belt of the Eastern Tibetan Plateau

AbstractThe Longmenshan Thrust Belt in Eastern Tibet resulted from a Mesozoic orogeny and Cenozoic reworking. It is generally believed that the Cenozoic tectonics along the Longmenshan Thrust Belt are mostly inherited from the Mesozoic. Reconstructing the Mesozoic tectonics of the Longmenshan Thrust Belt is therefore important for understanding its evolutionary history. On the basis of detailed structural analysis, we recognized a Main Central Boundary that divides the Longmenshan Thrust Belt into a Southeastern Zone and a Northwestern Zone. Both zones underwent a main D1 event characterized by D1E top-to-the-SE thrusting in the Southeastern Zone and D1W top-to-the-NW/N thrusting in the Northwestern Zone. In the Southeastern Zone, a D2 top-to-the-NW/N normal faulting that cuts the D1E structures is developed along the NW boundary of the basement complexes. Newly obtained and previous geochronological data indicate that the D1E and D1W events occurred synchronously at ca. 224–219 Ma, and the D2 top-to-the-NW/N normal faulting was episodically activated at ca. 166–160 Ma, 141–120 Ma, 81–47 Ma, and 27–25 Ma. Episodic and synchronously activated top-to-the-NW normal faulting and top-to-the-SE thrusting along the northwestern and southeastern boundaries of the basement complexes, respectively, leads us to propose that the basement slices were episodically imbricated to the SE during the Late Jurassic–Early Cretaceous and Late Cretaceous–earliest Paleocene. The D1 amphibolite facies metamorphic rocks above the basement complexes recorded fast exhumation during the Late Jurassic–Early Cretaceous. We propose that the early Mesozoic northwestward basement underthrusting along a crustal “weak zone” was responsible for the D1 double-vergent thrusting and amphibolite facies metamorphism. Subsequent basement-slice imbrications reworked the Longmenshan Thrust Belt and exhumed the amphibolite facies rocks. Our results highlight the importance of basement underthrusting and imbrication in the formation and reworking of the intracontinental Longmenshan Thrust Belt in Eastern Tibet.

Deep structure of the Salair fold-nappe terrane (NW CAOB) according to magnetotelluric sounding

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

Late Cretaceous aeolian desert system within the Mesozoic fold belt of South China: Palaeoclimatic changes and tectonic forcing of East Asian erg development and preservation

This study recognises and identifies the Late Cretaceous aeolian desert system from the Jianshi Basin, located in the intra-continental orogen within the Yangtze Block, South China. Erg deposits comprise aeolian dunes and dry aeolian sandsheets with alluvial facies associations at the margin and show an alluvial-aeolian depositional system. Palaeowind reconstruction of aeolian dune foresets showed that the dominant prevailing winds were westerlies, followed by northeasterlies and subordinate northwesterlies and southeasterlies. It is possible that monsoon rains recharged the water inflow system and caused the development of fluvial sand bodies at the margin of the Jianshi desert during the early deposition stage. The alluvial deposits in the study area were related to regional tectonism, while the dry aeolian system was dominated by mid- and low-latitudinal subtropical highs and the monsoonal climate. Orogenic topography, combined with planetary-scale subtropical high-pressure systems, blocked the transport of moisture, enclosed the low-lying land, and led to the aridification and development of desert depositional systems in the East Asian interior. Moreover, fault-controlled subsidence provided accommodation space in desert basins for alluvial and aeolian deposits. Based on the results obtained from palaeowind reconstructions, the divergent axis of subtropical highs during the Late Cretaceous was located in mid- and low-latitude areas of the Jianshi, Jianghan, Xinjiang, and Hengyang basins in South China. The relatively scattered nature of palaeowinds in the Jianshi Basin and adjacent deserts may indicate a seasonal drift in the divergent axis under the influence of a monsoonal climate.