scholarly journals Crustal deformation and exhumation within the India-Eurasia oblique convergence zone: New insights from the Ailao Shan-Red River shear zone

2021 ◽  
Author(s):  
B. Zhang ◽  
S.Y. Chen ◽  
Y. Wang ◽  
P.W. Reiners ◽  
F.L. Cai ◽  
...  
Keyword(s):  
Shear Zone ◽  
Middle Miocene ◽  
Shear Zones ◽  
Strike Slip ◽  
Red River ◽  
Crustal Thickening ◽  
The Core ◽  
Early Oligocene ◽  
Lateral Extrusion ◽  
Tectonic Boundaries

During the collision of India and Eurasia, regional-scale strike-slip shear zones played a key role in accommodating lateral extrusion of blocks, block rotation, and vertical exhumation of metamorphic rocks as presented by deformation on the Ailao Shan-Red River shear zone (ARSZ) in the Eastern Himalayan Syntaxis region and western Yunnan, China. We report structural, mica Ar/Ar, apatite fission-track (AFT), and apatite (U-Th)/He (AHe) data from the Diancangshan massif in the middle segment of the ARSZ. These structural data reveal that the massif forms a region-scale antiform, bordered by two branches of the ARSZ along its eastern and western margins. Structural evidence for partial melting in the horizontal mylonites in the gneiss core document that the gneiss experienced a horizontal shear deformation in the middle crust. Muscovite Ar/Ar ages of 36−29 Ma from the core represent cooling ages. Muscovite Ar/Ar ages of 25 and 17 Ma from greenschist-facies mylonites along the western and southern shear zones, respectively, are interpreted as recording deformation in the ARSZ. The AFT ages, ranging from 15 to 5 Ma, represent a quiescent gap with a slow cooling/exhumation in the massif. AHe results suggest that a rapid cooling and final exhumation episode of the massif could have started before 3.2 Ma, or likely ca. 5 Ma, and continue to the present. The high-temperature horizontal shearing layers of the core were first formed across the Indochina Block, locally antiformed along the tectonic boundaries, and then cooled through the mica Ar-Ar closure temperature during Eocene or early Oligocene, subsequently reworked and further exhumed by sinistral strike-slip movement along the ARSZ during the early Oligocene (ca. 29 Ma), lasting until ca. 17 Ma, then final exhumation of the massif occurred by dextral normal faulting on the Weixi-Qiaohou and Red River faults along the limbs of the ARSZ since ca. 5 Ma. The formation of the antiform could indicate local crustal thickening in an early transpressional setting corresponding to India-Asia convergence. Large-scale sinistral ductile shear along the ARSZ in the shallow crust accommodated lateral extrusion of the Indochina Block, and further contributed to the vertical exhumation of the metamorphic massif from the late Oligocene to the middle Miocene. Furthermore, the change of kinematic reversal and associated cooling episodes along the ARSZ since the middle Miocene or early Pliocene imply a tectonic transfer from strain localization along the major tectonic boundaries to continuous deformation corresponding to plateau growth and expansion.

High–pressure granulite–facies metamorphism and anatexis of deep continental crust: new insights from the Cenozoic Ailaoshan–Red River shear zone, SE Asia

2021 ◽  
Author(s):  
Haobo Wang ◽  
Shuyun Cao ◽  
Franz Neubauer ◽  
Junyu Li ◽  
Xuemei Cheng ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Shear Zone ◽  
Thermal Evolution ◽  
Shear Zones ◽  
Granulite Facies ◽  
Red River ◽  
Crustal Anatexis ◽  
Early Oligocene ◽  
Facies Metamorphism ◽  
T Path

<p>Studies of crustal anatexis have given valuable insights into the evolution of metamorphism–deformation and the tectonic processes at convergent plate margins during orogeny. The transition of metatexite to diatexite migmatite records crucial information about the tectono–thermal evolution and rheology of the deep crust. Along the Ailao Shan–Red River shear zone, metatexite migmatites, diatexite migmatites and leucogranites are widely distributed within the upper amphibolite and granulite facies zones of the Diancang Shan metamorphic complex. The high–pressure granulite–facies metamorphism with mineral assemblage comprising garnet + kyanite + K–feldspar + plagioclase + biotite + quartz + melt is first recognized from the patch metatexite migmatites in the complex. Detailed petrographic evidence and phase diagram reveal that the migmatite underwent nearly isothermal decompression metamorphism, presenting a clockwise P–T path. The peak metamorphic P–T conditions are constrained by phase diagram at ca. 11 kbar and 810 °C, and the amount of melt generated during heating is up to 18 mol%. The extraction and segregation of melts are evidenced by the presence of leucosomes within migmatites and leucogranite dikes, which record the melt flow network through the crust. Zircons and monazites from migmatites record the ages of the melting episode that began at ca. 36 Ma and lasted to ca. 20 Ma. All these results are in accord with orogenic crust thickening accompanied by pervasive anatexis during the Later Eocene to the early Oligocene in the Ailao Shan–Red River shear zone. Combined with available data related to the other continental–exhumed shear zone, we propose that the crustal anatexis has an important effect on the thermal–state of deep–seated shear zones, is thus controlling the rheological behavior of the lithosphere and plays the essential role in the initial localizing of shearing in the lower crust.</p>

Complex kinematics in a major ductile shear zone, NW Shetland: Evidence of ductile extrusion during Caledonian transpression

2021 ◽  
Author(s):  
Timothy Armitage ◽  
Robert Holdsworth ◽  
Robin Strachan ◽  
Thomas Zach ◽  
Diana Alvarez-Ruiz ◽  
...  
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Regional Scale ◽  
Shear Zones ◽  
White Mica ◽  
Strike Slip ◽  
Amphibolite Facies ◽  
Lateral Extrusion ◽  
Shear Sense ◽  
Ductile Shear

<p>Ductile shear zones are heterogeneous areas of strain localisation which often display variation in strain geometry and combinations of coaxial and non-coaxial deformation. One such heterogeneous shear zone is the c. 2 km thick Uyea Shear Zone (USZ) in northwest Mainland Shetland (UK), which separates variably deformed Neoarchaean orthogneisses in its footwall from Neoproterozoic metasediments in its hanging wall (Fig. a). The USZ is characterised by decimetre-scale layers of dip-slip thrusting and extension, strike-slip sinistral and dextral shear senses and interleaved ultramylonitic coaxially deformed horizons. Within the zones of transition between shear sense layers, mineral lineations swing from foliation down-dip to foliation-parallel in kinematically compatible, anticlockwise/clockwise-rotations on a local and regional scale (Fig. b). Rb-Sr dating of white mica grains via laser ablation indicates a c. 440-425 Ma Caledonian age for dip-slip and strike-slip layers and an 800 Ma Neoproterozoic age for coaxial layers. Quartz opening angles and microstructures suggest an upper-greenschist to lower-amphibolite facies temperature for deformation. We propose that a Neoproterozoic, coaxial event is overprinted by Caledonian sinistral transpression under upper greenschist/lower amphibolite facies conditions. Interleaved kinematics and mineral lineation swings are attributed to result from differential flow rates resulting in vertical and lateral extrusion and indicate regional-scale sinistral transpression during the Caledonian orogeny in NW Shetland. This study highlights the importance of linking geochronology to microstructures in a poly-deformed terrane and is a rare example of a highly heterogeneous shear zone in which both vertical and lateral extrusion occurred during transpression.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.0cf6ef44e5ff57820599061/sdaolpUECMynit/12UGE&app=m&a=0&c=d96bb6db75eed0739f2a6ee90c9ad8fd&ct=x&pn=gepj.elif&d=1" alt=""></p>

Exhumation of the crustal-scale Gaoligong strike-slip shear belt in Southeast Asia

2021 ◽  
pp. jgs2021-038
Author(s):  
Yanlong Dong ◽  
Shuyun Cao ◽  
Franz Neubauer ◽  
Haobo Wang ◽  
Wenyuan Li ◽  
...  
Keyword(s):  
Shear Zone ◽  
Early Cretaceous ◽  
Vertical Motion ◽  
Shear Zones ◽  
Strike Slip ◽  
Western Boundary ◽  
The Tibetan Plateau ◽  
Content Type ◽  
Lateral Extrusion ◽  
Supplementary Material

Lateral extrusion of blocks is a well-known geological process during continent–continent collision, which always expresses by either brittle strike-slip faults or ductile shear zones. However, vertical motion along such fault systems remains poorly constrained. The Gaoligong shear zone (GLG-SZ) formed the western boundary of the Indochina block during the India–Eurasia collision, resulting in the exhumation of deep crustal rocks, including a large volume of syntectonic granites. Combined zircon U-Pb dating and 40Ar/39Ar thermochronology revealed that both the unfoliated and foliated granitic intrusions were emplaced during the Early Cretaceous (112–125 Ma), post-magmatic melting occurred from the Early Oligocene (ca. 35 Ma), and subsequent cooling during the Middle Miocene (ca. 13 Ma). The average emplacement depth of Early Cretaceous samples revealed that at least 15 km of hangingwall of the GLG-SZ must have been removed by vertical motion during shearing. Syn-shearing exhumation underlines the role of the lateral motion of the shear zone initiation by magma-assisted rheological weakening and exhumation at high ambient temperatures within the shear zone. A new model links magmatic channel flow underneath the Tibetan Plateau with magma intrusions and the high geothermal gradients along the shear belts, such as the GLG-SZ.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5598365

scholarly journals Geometry, kinematics and regional significance of faulting and related lamprophyric intrusion in the mineralised zone at the Pu Sam Cap complex, Northwest Vietnam

2018 ◽  
Vol 40 (4) ◽  
pp. 320-340 ◽  
Author(s):  
Findlay R. H.
Keyword(s):  
Shear Zone ◽  
South China ◽  
Shear Zones ◽  
Planetary Science ◽  
Strike Slip ◽  
Red River ◽  
Fault System ◽  
Lateral Shear ◽  
Geological Society ◽  
Se Asia

The alkali volcanics and intrusive rocks, dated at around 35-33Ma, are cut by mineralised northeast and east trending faults showing predominant evidence for strike-slip. Mineralisation includes haematite-Au-Cu and is accompanied by iron-rich alteration of the volcanic rocks. Detailed assessment of the geometry of the fault system at Pu Sam Cap suggests that the faults formed as a Riedel shear system during left-lateral slip within the Song Hong-Song Chay shear zone and the numerous contemporaneous northwest trending faults to the south; the northeast trending faults are interpreted as dextral “book-end’’ faults between major northwest trending faults enclosing the Pu Sam Cap massif. As mineralisation is hosted within these faults and is also associated with lamprohyric dykes it confirms a thermal event younger than the alkaline volcanics and syenitic intrusives at Pu Sam Cap, suggesting a hidden, young porphyry system. The age of faulting, and thus the maximum age for this young intrusive event, is attributed to the 23-21Ma period of late-stage left-lateral strike-slip motion across northwest Vietnam.ReferencesAnczkiewicz R., Viola G., Muntener O., Thrirlwall M., Quong N.Q., 2007. Structure and shearing conditions in the Day Nui Con Voi massif: implications for the evolution of the Red River Fault. Tectonics 26: TC2002.Cao Shunyun, Liu Junlai, Leis B., Zhao Chunquiang 2010. New zircon U/Pb geochronology of the post-kinematic granitic plutons in Diancang Shan Massif along the Ailao-Shan-Red River Shear Zone and its geological implications. Acta Geologica Sinica (English Edition), 84, 1474-1487.Chung S.-L., Lee T., Lo C.,  et al., 1997. Intraplate extension prior to continental extrusion along the Ailao Shan-Red River shear zone.Geology, 25, 311-314.Cloos H., 1928. Experimentezurinnern Tektonik.  Zentralblatt fur Mineralogie und Palaeontologie, 1928, 609-621.Findlay R.H., Phan Trong Trinh 1997. The structural setting of the Song Ma region, Vietnam, and the Indochina-South China plate boundary problem. Gondwana Research, 1, 11-33.Jolivet L., Beysasac O., Goffe B., Avigad D., Leprevrier C., Maluski H., Ta Trong Thang, 2001. Oligo-Miocene midcrustal subhorizontal shear in Indochina. Tectonics, 20, 46-57.Khuong The Hung 2010. The complex tectonic events and their influence on formation of mineral deposits in northwest Vietnam. Unpublished PhD Thesis, University of Science and Technology, Cracow, 167p.Leloup P.H., N. Arnau,  R. Lacassin, J.R. Kienast, T.M. Harrison, P.T. Trinh, A. Replumaz and P. Tapponnier, 2001. New constraints on the structure, thermochronology and timing of the Ailao Shan - Red river shear zone, SE Asia, J. G. R., 106, 6657-6671.Leloup  PH.., R. Lacassin, P. Tapponnier, U. Scharer, Zhong Dalai, Liu Xaohan, Zhangshan, Ji Shaocheng and PT.Trinh, 1995. The Ailao Shan - Red river shear zone (Yunnan, China), Tertiary transform boundary of Indochina, Tectonophysics, 251, 3-84. Leprevier C., Maluski H., Nguyen Van Vuong, Roques D., Axente V., Rangin C., 1996. Indosinian NW-trending shear zones within the Truong Son belt, Vietnam: 40Ar-39Ar Triassic ages and Cretaceous to Cenozoic overprints. Tectonophysics, 283, 105-107.Lien-Sheng Zhang, Scharer U. 1999. Age and origin of magmatism along the Cenozoic Red River shear belt, China. Contributions to Mineralogy and Petrology, 134, 67-85.Nagy E.A., Scharer U., Minh N.T., 2000. Oligo-Miocene granitic magmatismin central Vietnam and implications for continental deformation in Indochina. Terra Nova, 12, 67-76.Nguyen Thi Bich Thuy, 2016. Isotop dating U-Pb Zircon of Syenit Formation, Pu Sam Cap. Journal of Geology, A Serie, 356, 30-36. (In Vietnamese).Pei-Long Wang, Ching-Hua Lo, Tung-Yi Lee, Sun-ling Chun, Ching-Yan Lan, Nguyen Trong Yem 1998. Thermochronological evidence for the movement of the Ailo Shan-Red River shear zone, a perspective from Vietnam. Geology, 26, 887-890.Phan Trong Trinh, Nguyen Trong Yem, Herve L.P., Tapponnier P., 1994. Late Cenozoic stress fields in North Vietnam from microtectonic measurements. Proceedings of the International Workshop on Seismotectonics and Seismic Hazard in Southeast Asia. Geological Survey of SR Vietnam, Hanoi, 182-186.Riedel W., 1929. Zur Mechanikgreologischer Brucherscheinungen. Zentralblatt fur Mineralogie und Palaeontologie, Abhandlung B, 354-368.Scharer U., Tapponnier P., Lacassin R., Leloup P.H., Dalai Z., Shaosheng J., 1990. Intraplate tectonics in Asia: a precise age for large-scale Miocene movement along the Ailao Shan-Red River shear zone, China. Earth  and Planetary Science Letters, 97, 65-77.Scharer U., Zhang L.S., Tapponnier P., 1994. Duration of strike-slip movements in large shear zones: the Red River belt, China. Earth and Planetary Science Letters, 126, 379-397.Searle M.P., 2006. Role of the Red River Shear zone, Yunnan and Vietnam, in the continental extrusion of SE Asia. Journal of the Geological Society, London, 163, 1025-1036.Searle M.P., Meng-Wan Yeh, Te-Hsien Lin, Sun-Lin Chung, 2010. Structural constraints on the timing of left-lateral shear along the Red River shear zone in the Ailao Shan and Diancang Shan Ranges, Yunnan, SW China. Geosphere, 6, 316-338.Tapponnier P., Lacassin R., Leloup H., Scharer U., Zhong Dalai, Wu Hawei, Liu Ziaohan, Ji Shaocheng, Zhang Lianshang, Zong Jiayou, 1990. The Ailao Shan/ Red River metamorphic belt: Tertiary left-lateral shear between Indochina and south China. Nature, 342, 431-437.Tchalenko J.S., 1970.  Similarities between shear zones of different magnitudes. Bulletin of the Geological Society of America, 81, 1625-1640.Viola G., Anczkiewicz R. 2009. Exhumation history of the Red River shear zone in northern Vietnam:  new insights from zircon and apatite fission-track analysis. Journal of Asian Earth Sciences, 33, 78-90.Yang Yiseng, Hong Qun, Hu Huan-ting, Hieu Pham Trung, Nguyen Thi Bich Thuy, Chen Fu-kun, 2013. Geochemical characteristics and genesis of the Cenozoic porphyry in the Laizhou area, northwestern Vietnam. Acta Petrologica Sinica, 29(3), 899-911. (In Chinese with English abstract, full English version through Google Translate).

scholarly journals Migmatite and leucogranite in a continental-scale exhumed strike-slip shear zone: Implications for tectonic evolution and initiation of shearing

2021 ◽  
Author(s):  
Junyu Li ◽  
Shuyun Cao ◽  
Xuemei Cheng ◽  
Franz Neubauer ◽  
Haobo Wang ◽  
...  
Keyword(s):  
Shear Zone ◽  
Thermal State ◽  
Shear Zones ◽  
Strike Slip ◽  
Red River ◽  
Crustal Anatexis ◽  
Plate Convergence ◽  
Continental Scale ◽  
Geological Processes ◽  
Lower Crustal

Plutons within continental strike-slip shear zones bear important geological processes on late-stage plate transpression and continent-continent collision and associated lateral block extrusion. Where, when, and how intrusions and shearing along transpressional strike-slip shear zones respond to plate interactions, however, are often debated. In this study, we investigated migmatite associated leucogranite and pegmatite from the exhumed >1000-km-long Ailao Shan-Red River left-lateral strike-slip shear zone in Southeast Asia that was active during India-Eurasia plate convergence. Most zircons from the migmatites and leucogranitic intrusions present inherited core-rim structure. The depletion of rare earth element patterns and positive Eu anomalies suggest that leucosomes and leucogranites are the result of crustal anatexis. Zircon rims from the foliated migmatites and leucogranites record U-Pb ages of 41−28 Ma, revealing the timing of the Cenozoic crustal anatexis event along this strike-slip shear zone. Ages of the magmatic zircons from the unfoliated pegmatites provide the timing of the termination of a high-temperature tectono-thermal event and ductile left-lateral shearing at 26−23 Ma. The Cenozoic crustal anatexis along the Ailao Shan-Red River strike-slip shear zone indicates that thickened crust underneath the shear zone involved previously subducted crust. We propose that the Cenozoic thermal state has an important effect on the crustal anatexis and thus on the rheological behavior of the lithosphere by thermal weakening, which plays an essential role in localizing the initiation of the deep-seated lower-crustal shear zone.

Cenozoic rifting and inversion of Beibuwan Basin and its linkage with the strike-slip movement along the Ailao Shan-Red River Shear Zone

2021 ◽  
pp. 1-18
Author(s):  
Yanjun Cheng ◽  
Zhiping Wu ◽  
Jie Zhang ◽  
Yuqing Liu ◽  
Zhengkai Wang ◽  
...  
Keyword(s):  
Shear Zone ◽  
Strike Slip ◽  
Red River ◽  
And Inversion ◽  
Strike Slip Movement

Macro- and microstructural analysis of the Zhujiafang ductile shear zone, Hengshan Complex: Tectonic nature and geodynamic implications of the evolution of Trans−North China orogen

2020 ◽  
Author(s):  
Lingchao He ◽  
Jian Zhang ◽  
Guochun Zhao ◽  
Changqing Yin ◽  
Jiahui Qian ◽  
...  
Keyword(s):  
Shear Zone ◽  
North China ◽  
Shear Zones ◽  
Crustal Thickening ◽  
Slip Systems ◽  
High Grade ◽  
Ductile Shear Zone ◽  
Crustal Rocks ◽  
Ductile Shear ◽  
Lower Crustal

In worldwide orogenic belts, crustal-scale ductile shear zones are important tectonic channels along which the orogenic root (i.e., high-grade metamorphic lower-crustal rocks) commonly experienced a relatively quick exhumation or uplift process. However, their tectonic nature and geodynamic processes are poorly constrained. In the Trans−North China orogen, the crustal-scale Zhujiafang ductile shear zone represents a major tectonic boundary separating the upper and lower crusts of the orogen. Its tectonic nature, structural features, and timing provide vital information into understanding this issue. Detailed field observations showed that the Zhujiafang ductile shear zone experienced polyphase deformation. Variable macro- and microscopic kinematic indicators are extensively preserved in the highly sheared tonalite-trondhjemite-granodiorite (TTG) and supracrustal rock assemblages and indicate an obvious dextral strike-slip and dip-slip sense of shear. Electron backscattered diffraction (EBSD) was utilized to further determine the crystallographic preferred orientation (CPO) of typical rock-forming minerals, including hornblende, quartz, and feldspar. EBSD results indicate that the hornblendes are characterized by (100) <001> and (110) <001> slip systems, whereas quartz grains are dominated by prism <a> and prism <c> slip systems, suggesting an approximate shear condition of 650−700 °C. This result is consistent with traditional thermobarometry pressure-temperature calculations implemented on the same mineral assemblages. Combined with previously reported metamorphic data in the Trans−North China orogen, we suggest that the Zhujiafang supracrustal rocks were initially buried down to ∼30 km depth, where high differential stress triggered the large-scale ductile shear between the upper and lower crusts. The high-grade lower-crustal rocks were consequently exhumed upwards along the shear zone, synchronous with extensive isothermal decompression metamorphism. The timing of peak collision-related crustal thickening was further constrained by the ca. 1930 Ma metamorphic zircon ages, whereas a subsequent exhumation event was manifested by ca. 1860 Ma syntectonic granitic veins and the available Ar-Ar ages of the region. The Zhujiafang ductile shear zone thus essentially record an integrated geodynamic process of initial collision, crustal thickening, and exhumation involved in formation of the Trans−North China orogen at 1.9−1.8 Ga.

scholarly journals Exploring the relationships between shear zones and granites: field and microstructural data for contrasting case studies of the Borborema Province (NE Brazil)

2021 ◽  
Vol 21 (2) ◽  
pp. 3-18
Author(s):  
Lauro Cézar Montefalco de Lira Santos ◽  
Luís Gustavo Ferreira Viegas
Keyword(s):  
Case Studies ◽  
Shear Zones ◽  
Strike Slip ◽  
West Gondwana ◽  
The Core ◽  
Borborema Province ◽  
Magmatic Fabric ◽  
Quartz Grains ◽  
Melt Pockets ◽  
Microstructural Data

We discuss meso- and microstructural features of granites closely related to strike-slip shear zones in the Borborema Province, NE Brazil. The Riacho do Icó stock is an en-cornue intrusion aged at ca. 607 Ma. Magmatic fabric is recorded in the core of the granite, whilst increasing deformation is marked by the development of mylonitic fabrics towards the Afogados da Ingazeira shear zone, including magmatic foliation and lineation rotation. Early recrystallization of quartz and K-feldspar crystals is widespread as a fabric with well-developed granoblastic polygonal textures and lobate subgrain boundaries, heterogeneously deformed lenses and ameboid quartz ribbons, typical of igneous rocks submitted to deformation in deep crustal levels. On the other hand, the Espinho Branco-Santa Luzia leucogranitic belt is hosted along the Patos Lineament, aged between the ca. 575 – 565 Ma interval. These rocks show discordant relationships with the host migmatites and the main deformational fabric is characterized by a dominant magmatic foliation that is locally overprinted by structures that are typical of solid-state flow. Quartz melt pockets and interstitial quartz grains filling fractures in feldspar clasts are common. Such characteristics are compatible with granites that were injected in the continental crust along planar anisotropies (i.e., shear zones) formed during the late-stage partial melting events that originated the migmatites of the area. The case studies are proxies in the understanding of different episodes of magma emplacement along shear zones in this part of West Gondwana.

A lifetime of the Variscan orogenic plateau from uplift to collapse as recorded by the Prague Basin, Bohemian Massif

2017 ◽  
Vol 156 (3) ◽  
pp. 485-509 ◽  
Author(s):  
FRANTIŠEK VACEK ◽  
JIŘÍ ŽÁK
Keyword(s):  
Bohemian Massif ◽  
Three Dimensional ◽  
Plate Boundary ◽  
Early Carboniferous ◽  
Shear Zones ◽  
Crustal Thickening ◽  
Variscan Orogeny ◽  
Prague Basin ◽  
Lateral Extrusion ◽  
Orogenic Plateau

AbstractThe Ordovician to Middle Devonian Prague Basin, Bohemian Massif, represents the shallowest crust of the Variscan orogen corresponding toc.1–4 km palaeodepth. The basin was inverted and multiply deformed during the Late Devonian to early Carboniferous Variscan orogeny, and its structural inventory provides an intriguing record of complex geodynamic processes that led to growth and collapse of a Tibetan-type orogenic plateau. The northeastern part of the Prague Basin is a simple syncline cross-cut by reverse/thrust faults and represents a doubly vergent compressional fan accommodatingc.10–19 % ~NW–SE shortening, only minor syncline axis-parallel extension and significant crustal thickening. The compressional structures were locally overprinted by vertical shortening, kinematically compatible with ductile normal shear zones that exhumed deep crust in the orogen's interior atc. 346–337 Ma. On a larger scale, the deformation history of the Prague Syncline is consistent with building significant palaeoelevation during Variscan plate convergence. Based on a synthesis of finite deformation parameters observed across the upper crust in the centre of the Bohemian Massif, we argue for a differentiated within-plateau palaeotopography consisting of domains of local thickening alternating with topographic depressions over lateral extrusion zones. The plateau growth, involving such complex three-dimensional internal deformations, was terminated by its collapse driven by multiple interlinked processes including gravity, voluminous magma emplacement and thermal softening in the hinterland, and far-field plate-boundary forces resulting from the relative dextral motion of Gondwana and Laurussia.

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