Slab tear along a subducting passive margin and related Late Triassic E-MORB/OIB-affinity magmatism in southeastern Tibet

A joint subduction of the oceanic-continental plates exerts primary controls on the tectonomagmatic activities alongside trench-perpendicular ocean-continental transitional (OCT) belts (i.e., passive continental margin). Such OCT belts with a rheological boundary trigger substantial great crustal density contrast since lateral pressure gradients create where a mature oceanic lithosphere terminate against a thicker continental lithosphere. This study investigates the conjunction between the southernmost segment of the ~1500-km-long, NW–SE-trending Yushu–Yidun Arc Belt and the NE–SW trending Longmen Shan Fault system in southeastern Tibet, to explore the interaction of these two large-scale linear structures. A compilation of geological evidence reveals that an OCT belt previously defined the Longmen Shan Fault, separating the South China Continent from the Garze–Litang Ocean. During the southwestward subduction of the Garze-Litang oceanic lithosphere, this OCT belt which lies on the southeastern edge was reacted with the subduction of the oceanic lithosphere, and subsequently induced slab tearing of its subduction front causing the upwelling of the asthenosphere. This model interprets favorably the intriguing geology of the triangle-shaped Songpan–Garze–Hoh Xil terrane as well as the generation of the Late Triassic enriched mid-ocean ridge basalts or ocean island basalts (EOB) at the southernmost segment of the Yushu–Yidun Arc Belt, where the asthenosphere-sourced mafic lavas are tightly intercalated with normal arc-like igneous rocks in a continental arc.