Determination of material composition of Jinshajiang tectonic mélange belt in Gonjo-Baiyu area, eastern Tibet

The Jinshajiang tectonic mélange belt has preserved a large amount of important information on deformation, metamorphism and magmatism related to the formation and expansion of the paleo Tethys, ocean-continent subduction, ocean basin closure and continent-continent collision, and is an important window to study collision orogeny and plate tectonics. Based on the 1∶50000 regional geological survey of Gonjo-Baiyu area in eastern Tibet, combined with the results of indoor thin section identification, rock geochemical analysis and chronological test, this paper makes a detailed determination of the material composition and structural deformation characteristics of Jinshajiang tectonic mélange belt. The Jinshajiang tectonic mélange belt in Gonjo-Baiyu area, eastern Tibet is mainly composed of a series of tectonic blocks with different scales, lithology and deformation degree and strongly deformed matrix. The rock blocks are connected in a network by many ductile brittle ductile faults nearly parallel to the strike of the junction zone, showing the characteristics of locally ordered and globally disordered tectonic mélange. Tectonic blocks mainly include: ultrabasic-basic rock, marble, marble + metamorphic basic rock, eclogite or eclogite, metamorphic silica-limestone-argillaceous rock, etc. Matrix materials mainly include garnet bearing schist and schist. The geochemical analysis data of rocks reveal that the original rocks of basic rock blocks have the characteristics of enriched mid ocean ridge or normal mid ocean ridge basic rocks (E-MORB, N-MORB). The metamorphic basic volcanic rocks in the ocean island seamount block have the characteristics of ocean island basalt (OIB); The protolith of eclogite has the characteristics of ocean island basalt (OIB) or normal mid ocean ridge basalt (N-MORB). Combined with previous research results, it can be finely divided into five main evolution stages: rift valley basin (D), ocean basin expansion (C₁-P₁), ocean crust subduction (P₂-P₃), arc continent collision orogeny (T₁-T₂) and superimposed volcanic rift basin (T₂²-T₃¹).