Crust-mantle resistivity structure and its implications for Indosinian granitoid genesis in the West Qinling orogenic belt, NE Tibetan Plateau

Abstract

The West Qinling orogenic belt (WQOB), which formed during the convergence between the North China Block (NCB) and South China Block (SCB), is characterized by extensive Indosinian granitoids that provide fundamental material sources for large-scale mineralization. Despite their significance, the genesis of these Indosinian granitoids remains contentious. To resolve this long long-standing debate, we conducted high density broadband magnetotelluric (BBMT) sounding surveys across the WQOB and its adjacent areas. Based on three-dimensional inversion of the BBMT data, we constructed a high-resolution resistivity model extending to a depth of 100 km. The model results reveal discontinuous low-resistivity bodies within the middle and lower crust beneath the WQOB, as well as a large-scale medium-lower resistivity anomaly zone (MLRZ) spanning the crust and upper mantle. These electrical features indicate the presence of partial crustal melting and mantle upwelling in the study region. The obtained resistivity structure provides compelling evidence for the existence of the Bayan Har Ocean (BHO), in addition to the Mianlue Ocean, between the WQOB and the Sichuan Basin from the Early Devonian to Late Permian. The closure of the BHO is inferred to be driven by the renewed thrust faulting of the SCB. Furthermore, we propose an updated evolutionary model for the Paleo-Tethys oceans in this study area. Which records complex, multi-stage deep dynamic processes. The generation of Indosinian granitoids was jointly controlled by the progressive closure of the Mianlue Ocean and the subduction of the BHO, which could effectively explaining the distinct zonation and temporal characteristics of Indosinian granitoid magmatism in the region Our integrated interpretation not only sheds new light on the contentious petrogenesis of Indosinian granitoids, but also provides novel insights into the tectonic evolution of the northeastern Tibetan Plateau.