11 - A model for the tectonic history of HP and UHPM regions in east central China

Summary

Abstract

The South Qinling-Dabie Mountains orogenic complex in east central China exposes deep sections of continental crust that were metamorphosed under high and ultrahigh pressure (HP-UHP) conditions during Triassic continental collision. This chapter presents a tectonic model for collision, metamorphism, and exhumation of the HP-UHP rocks in east central China that incorporates ⁴⁰Ar/³⁹Ar ages, geothermobarometric and structural data collected from this area, and published regional geophysical and geologic information.

Two new ideas proposed in this tectonic synthesis of east central China are, first, that exhumation of the HP-UHP rocks occurred in two episodes marked by different exhumation rates, and second, that these rates were probably associated with different tectonic processes. The first stage of exhumation was probably fairly rapid and was accomplished through continuous collision, stacking of continental crustal wedges via crustal-scale thrusts, and lateral translation in the upper crust along strike-slip faults. The second identifiable stage of exhumation, which finally brought the HP-UHP rocks to the surface, occurred at relatively slower rates than in the first stage, and was associated with processes of crustal extension, anatexis, and erosion.

Introduction

Discoveries in continental collision zones of metamorphic minerals generated under high and ultrahigh pressure (HP-UHP) conditions attest to former continental crustal thicknesses greater than any currently estimated on the Earth.