Detachment fault system in the Zedang ophiolite of southern Tibet: New insights into the evolution of the neo-Tethys ocean

Abstract

The Zedang ophiolite in the Yarlung Zangbo Suture Zone of southern Tibet provides crucial insights into the tectonic evolution of the Neo-Tethys Ocean. This study presents the first detailed characterization of a detachment fault system within the ophiolite, which primarily occurs along the southern boundary of peridotite massifs. The system is marked by serpentinite shear zones at the top of the mantle peridotite, forming a tectonic contact between the peridotite massifs and the overlying Bainang terrane. The structural, lithological, and deformation characteristics of the shear zone closely resemble those observed in oceanic core complexes at modern slow-spreading ridges and in Alpine ophiolites. Zircon U-Pb dating of an undeformed gabbro dike intruding the serpentinized peridotite (125.0 ± 0.4 Ma) and a basalt flow directly overlying the detachment fault (124.2 ± 1.0 Ma) indicates that Early Cretaceous magmatic activity occurred following the primary deformation and exhumation stage. Comparative analysis with the Xigaze ophiolite reveals heterogeneous development along the Neo-Tethys ridge system. While the Xigaze ophiolite formed at a slow- or ultraslow-spreading ridge with a more abundant magma supply, the Zedang ophiolite likely originated in a magma-deficient environment characterized by pronounced tectonic extension and episodic magmatism. These findings provide new constraints on the geodynamic processes that shaped the Neo-Tethys Ocean prior to the India–Asia collision.