Contributions of Triassic Tectonism to Build the Northern Tibetan Plateau: Insights From Tectonic Evolution of the Jinhongshan Range, Central Altyn Tagh Fault System

Abstract

AbstractClarifying the contributions of pre‐Cenozoic and especially the Mesozoic tectonism to build crustal architecture of the Tibetan plateau is important, especially for evaluating the role of Cenozoic Indo‐Asian collision in creating the present‐day plateau. However, how the Mesozoic tectonism evolved and its influence on the Cenozoic strain distribution remain enigmatic. We provide constraints on these issues by reporting evidence of Triassic (232–223 Ma) and Eocene crustal shortening in the Jinhongshan range of North Tibet, based on coupled structural, zircon U‐Pb, and40Ar/39Ar studies. Triassic shortening was accomplished by two stages manifested as top‐SSE thrust shear (D1) followed by sinistral oblique shear along the ENE trending Jinhongshan shear zone and tight folding (D2), related to ~NNE‐SSW transpression under greenschist‐ to amphibolite‐facies conditions. Such shortening occurred coevally with regional‐scale magmatism, cooling, and exhumation, indicating significant Mesozoic tectonism capable of generating thickened crust and high elevation of North Tibet. We attributed the shortening to far‐field stress effects of terrane collisions between Kunlun and Qiangtang, in which the comparable Jinhongshan and Dangjin shear zones might have formed a continuous, high‐strain zone accommodating relative motion between Tarim and Kunlun‐Qaidam. Eocene shortening (D3) is documented by ENE trending open folds and thrusts, kinematically compatible with left‐lateral activity along the Cenozoic Altyn Tagh fault system. The Triassic Jinhongshan‐Dangjin zone shows a spatial consistency with the Cenozoic Altyn Tagh fault system, implying that at least some segments of this Cenozoic fault system follow more ancient structures. Such evidence reinforces a decisive role of the Triassic tectonic discontinuity in localizing Cenozoic deformation.