The Late Jurassic high-Mg diorite and Early Cretaceous high-silica granite in central Tibet: Implication for the subduction process of the Meso-Tethys Ocean

Abstract

The evolutionary process and subduction polarity related to the Shiquanhe-Nam Co segment of the Meso-Tethys Ocean remains a significant point of controversy. High-Mg diorite is a special type of rock formed at convergent plate margins, which are typically associated with young subducting plates. This study investigates the petrogenesis and spatial-temporal distribution of Late Jurassic high-Mg diorites and Early Cretaceous high-silica granites in central Tibet to shed light on the subduction processes of the Meso-Tethys Ocean. The Late Jurassic high-Mg diorites formed through metasomatic interactions between mantle wedge peridotite and melts derived from subducted sediments. These diorites subsequently underwent fractional crystallization of clinopyroxene, amphibole, and plagioclase. Coeval granodiorites display evidence of magma mixing and fractional crystallization of amphibole, plagioclase, and pyroxene. In contrast, the Early Cretaceous high-silica granites originated from the partial melting of metandesites, followed by fractional crystallization of plagioclase and biotite. Magmatic activity within the central Lhasa terrane exhibited a southward migration from 170 to 160 Ma and a subsequent northward shift from 150 to 135 Ma. These findings suggest that Late Jurassic magmatic activity was driven by the initial southward subduction of the Meso-Tethys oceanic crust, which provided the necessary heat for crustal remelting. In the Early Cretaceous, the magmatic record reflects slab rollback, which facilitated mantle upwelling, the formation of new crust, and a northward migration of magmatism. This study provides new constraints on the tectono-magmatic evolution of the Meso-Tethys Ocean.