Petrostructural and Geochronological Constraints on Devonian Extension‐Shortening Cycle in the Chinese Altai: Implications for Retreating‐Advancing Subduction - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Tectonics Année : 2022

Petrostructural and Geochronological Constraints on Devonian Extension‐Shortening Cycle in the Chinese Altai: Implications for Retreating‐Advancing Subduction

Lingzhu Kong
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Yingde Jiang
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Karel Schulmann
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Jian Zhang
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Roberto F. Weinberg
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Min Sun
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Sheng Wang
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Tan Shu
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Jun Ning
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Résumé

Structural and metamorphic effects of a Devonian extension-shortening cycle in the NW Chinese Altai were investigated using combined structural-petrological analysis and zircon and monazite U-Pb geochronology. Structural observations revealed a ubiquitous, sub-horizontal metamorphic fabric (S1), which was originally sub-parallel with horizontal bedding (S0) of supracrustal Devonian volcanic-sedimentary basins. This metamorphic fabric is defined by a sillimanite-bearing migmatitic gneissosity associated with extensional shear bands and a cordierite-bearing schistosity in the orogenic lower and middle crust, respectively. Staurolite relics preserved in the S1 fabric are interpreted as relics of older, higher pressure Barrovian-type metamorphism. These structural-metamorphic features are correlated with decompression and heating and interpreted as reflecting a crustal-scale extensional phase. S1 was folded to form N-S-oriented upright antiforms cored by migmatites and locally transposed by steep S2 foliation during a ∼W-E-directed shortening (in current coordinates). Andalusite and cordierite overgrew the migmatitic S2 foliation attesting to decreasing pressure associated with vertical extrusion of migmatites in cores of F2 antiforms. New U-Pb age data from subhorizontally foliated migmatites suggest that the D1 extension started at least before ∼410 Ma. Age data of syn-D2 granite intrusions and dykes constrain the D2 shortening starting soon after D1 extension and ending at ∼378 Ma. Combined with regional data, cycles of extensional and contractional tectonic regimes can be defined, which also show eastward migration along-strike of the Altai range. Such extension-shortening cycles could result from alternating retreating and advancing subduction, which governed the evolution of the Altai accretionary system from the Ordovician until the Carboniferous.
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hal-04222092 , version 1 (07-12-2023)

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Lingzhu Kong, Yingde Jiang, Karel Schulmann, Jian Zhang, Roberto F. Weinberg, et al.. Petrostructural and Geochronological Constraints on Devonian Extension‐Shortening Cycle in the Chinese Altai: Implications for Retreating‐Advancing Subduction. Tectonics, 2022, 41 (9), ⟨10.1029/2021TC007195⟩. ⟨hal-04222092⟩
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