Magnetotelluric evidence for the multi-microcontinental composition of eastern South China and its tectonic evolution

Zhang Kun,Guangming Fu,Lü Qingtian,Hao Hu,Jinhua Zhao,Jiayong Yan,Fan Luo,Xin Tao

doi:10.1038/s41598-020-69777-3

Abstract

The tectonic boundaries and geodynamic evolution of the South China Block are widely debated. While the community largely agrees on the occurrence of the collision between the Yangtze and Cathaysia Blocks, the lack of ultrahigh-pressure metamorphic rocks and obscurity of the boundary lead to inconsistencies among the abundant geological and geophysical data. We present three profiles that reveal the geoelectrical structure of eastern South China. Distinct conductive interfaces oriented NE–SW are identified in the geoelectrical lithosphere, which separate the region into six parts. To interpret our observations and resultant model, we develop and propose a mechanism of “microcontinent interaction”. Our new model justifies the prior proposed models of ‘block collision’ and additionally proposes ‘multi-terrane accretion-collision’ to address the tectonic evolution.

Highlights

The tectonic boundaries and geodynamic evolution of the South China Block are widely debated
With the closure of the South China Ocean, South China was formed from the Neoproterozoic collision of the Cathaysia and Yangtze Blocks[1], where the Jiangnan orogenic belt marks the suture[2], and was generally accepted to have collided with North China from the Indo-Sinian to the early Yanshanian (Mesozoic), forming the Dabie orogenic belt and the Lower Yangtze depression on the northern margin of eastern South China (e.g.,3,4) (Fig. 1)
Recent geological evidence, such as the discovery of distinct multistage magmatic and metamorphic events in the western and eastern parts of Cathaysia, tends to favor multiple terranes involved in South China and especially indicates that Cathaysia was a result of accretion and collision between West Cathaysia and East C athaysia[8], which used to be separated

Summary

Introduction

The tectonic boundaries and geodynamic evolution of the South China Block are widely debated. This thesis led to wide debates on the tectonic boundaries and processes of the continent (e.g.,3,5–7) Recent geological evidence, such as the discovery of distinct multistage magmatic and metamorphic events in the western and eastern parts of Cathaysia, tends to favor multiple terranes involved in South China and especially indicates that Cathaysia was a result of accretion and collision between West Cathaysia and East C athaysia[8], which used to be separated. Several extensive crustal/lithospheric thinning subregions revealed by the velocity model from a seismic study indicate the nonuniformity of the lithosphere[9] This contradiction suggests that the interactions of microcontinents and the geodynamic processes of intracontinental tectonic evolution were more complex than previously predicted and may not be explained by a single simple mechanism, which implies the need for robust and higher resolution constraints on the physics of the lithosphere. S1–S4 represent the “traces” of intracontinental subducted slabs, L1–L4 represent the top interfaces of the slabs, and “N” (S2-N, L2-N) indicates the Nanling Range

Methods

Discussion

Conclusion