Late Triassic-Early Jurassic dextral oblique subduction of the Meso-Tethys Ocean unraveled from mélange shear fabrics of the Bangong-Nujiang suture: Regional and global tectonic implications

The Bangong-Nujiang suture zone (BNSZ) preserves extensive ophiolitic mélanges generated during the Meso-Tethys subduction, but their shear fabrics, critical records of subduction dynamics, remain poorly studied. This study presents a detailed structural analysis of BNSZ mélange fabrics in western-central Tibet, identifying five deformation phases and foliations: symmetric (S1) and asymmetric (S2) block-in-matrix fabrics, ESE-trending reverse faults/folds (S3), NE-trending reverse faults/folds (S4), and ESE-trending normal faults (S5). The S1-S3 foliations represent progressive deformation from underthrusting to tectonic underplating along the subduction channel. S4 reflects wedge modification driven by seamount subduction during the latest Triassic. S5-related extension reflects a transition to subduction erosion in the Middle-Late Jurassic, which exhumed underplated ophiolitic mélanges. Quantitative kinematic restoration using S2 shear fabrics indicates northwestward oblique subduction characterized by high obliquity (~20°) in the Late Triassic, which shifted to moderate obliquity (~48°) in the Early Jurassic. The oblique subduction likely contributed to the >20 myr magmatic quiescence in South Qiangtang following subduction initiation at ~220Ma. Regionally, dextral oblique subduction characterized the entire northern Meso-Tethyan active margin, driving widespread hinterland dextral shear, including the trans-Eurasian “Silk Road transpression”. These kinematics were coeval with rapid Paleo-Pacific plate spreading, suggesting a potential Tethyan-Panthalassan geodynamic linkage.