Early Mesozoic thrust tectonics of the northwest Zhejiang region (Southeast China)

Abstract

The NW Zhejiang region of South China occupies a key tectonic position near the suture zone of the Yangtze and Cathaysian blocks and is of critical importance for the assembly of East Asia. Sedimentological and tectonic analyses indicate that the region had a SE-dipping paleoslope in the late Paleozoic to Early Triassic. A transitional sedimentary environment from deep sea to continental molasse is documented in the early Triassic– late Triassic interval. Associated structures are NW-vergent folds and thrusts that root southeastward beneath the high-grade Chencai metamorphic complex. The structural styles of this foreland fold-and-thrust belt are characterized by multifold duplexes and individual folds that are together zoned from SE to NW as follows: (1) core zone characterized by shear folds and ductile thrusts; (2) SE belt with out-of-sequence thrusting of multifold duplexes and an average shortening of 50%; (3) central belt with duplexes, imbricate fans, and an average shortening of 40%; and (4) NW belt with Jura-type folds and a shortening of ~10%. A tectonic model for the foreland fold-and-thrust belt is discussed in relation to the early Mesozoic archipelago paleogeography of South China.