1. Architecture and P-T-deformation-time evolution of the Chinese SW-Tianshan HP/UHP complex: Implications for subduction dynamics
- Author
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Benoit Caron, Léa Bayet, Zhou Tan, Timm John, Tuo Jiang, Tao Hong, Bo Wan, Jun Gao, Philippe Agard, Patrick Monié, Xin-Shui Wang, University of Chinese Academy of Sciences [Beijing] (UCAS), Institut des Sciences de la Terre de Paris (iSTeP), Institut national des sciences de l'Univers (INSU - CNRS)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA), Shandong University, Physics of Geological Processes [Oslo] (PGP), Department of Physics [Oslo], Faculty of Mathematics and Natural Sciences [Oslo], University of Oslo (UiO)-University of Oslo (UiO)-Faculty of Mathematics and Natural Sciences [Oslo], University of Oslo (UiO)-University of Oslo (UiO)-Department of Geosciences [Oslo], University of Oslo (UiO)-University of Oslo (UiO), Institut für Geologische Wissenschaften, Freie Universität Berlin, Laboratory of Isotope Geochemistry, Wuhan Centre of China Geological Survey, University of Ottawa [Ottawa] (uOttawa), Centre National de la Recherche Scientifique (CNRS)-Sorbonne Université (SU)-Institut national des sciences de l'Univers (INSU - CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Université des Antilles (UA)-Centre National de la Recherche Scientifique (CNRS), Laboratory of Isotope Geochemistry [Wuhan], China Geological Survey, and University of Ottawa [Ottawa]
- Subjects
Blueschist ,010504 meteorology & atmospheric sciences ,Subduction ,Cold subduction regim ,Lithology ,Metamorphic rock ,Subduction dynamics ,P-T-deformation-time historie ,40Ar-39Ar in situ laser ablation analyse ,Window (geology) ,010502 geochemistry & geophysics ,01 natural sciences ,Phengite ,Juxtaposition ,[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry ,General Earth and Planetary Sciences ,UHP/HP metamorphism ,Chinese SW-Tianshan ,Eclogite ,Petrology ,Geology ,0105 earth and related environmental sciences ,Zircon - Abstract
International audience; We present the first comprehensive P-T-deformation-time and kinematic constraints for HP/UHP eclogite, blueschist and greenschist-facies metavolcano-sedimentary rocks cropping out in the Chinese SW-Tianshan metamorphic complex (within the ~30 km wide N-S Akeyazi-Kebuerte area). We reappraise this HP/UHP “mélange”, which should be divided into three main tectonic units, from north to south, according to their discrepant lithologies and P-T-time-deformation histories. These three units crop out in a tectonic window beneath greenschist-facies metavolcanics. P-T estimates point to 1) UHP-LT conditions around 2.6–2.9 GPa at ~520 °C for the metavolcano-sedimentary rocks of the northern HP/UHP unit, 2) HP-LT conditions of 1.8–2.1 GPa and ~500 °C for the central blueschist horizon and 3) lower-blueschist facies conditions of 1.0–1.5 GPa at ~485 °C for the southern ultramafic-mafic unit. In situ laser probe Ar-Ar age constraints (with textural control) on recrystallized phengites from the HP/UHP unit cluster within 315 to 325 Ma. Phengite ages from the central blueschist horizon are 10–15 Ma older, at ~325–345 Ma. Laser-ICP-MS U-Pb dating on zircon from the south ultramafic-mafic unit yield ages around ~360 Ma for metamorphic overgrowths. In contrast, step-heating Ar-Ar phengite age constraints for the greenschist-facies metavolcano-sediments fall within 280–300 Ma. These new field and P-T-time data disclose an episodic exhumation of three main tectonic slices, respectively from ~85 km, ~65 km and ~45 km depths, and a progressive change of metamorphic gradients from ~12 to ~6–7 °C/km, which could reflect a cooling of the subduction system with time. Final juxtaposition at ~20 km was probably achieved around 300 Ma, prior to collision.
- Published
- 2019