Low‐Temperature Thermochronological Perspective on Geodynamic Evolution of the Cathaysia Block Since Early Mesozoic

Abstract

Mesozoic intrusive rocks are extensively outcropped in the Cathaysia Block (CB), indicating that they underwent significant exhumation after being formed. However, tectonothermal evolution of the CB during Mesozoic-Cenozoic times is still poorly constrained and associated geodynamic mechanisms driving the regional exhumation remain elusive. Toward this end, we present first zircon and apatite (U-Th)/He data of eight Mesozoic granitic plutons distributed across the intracontinental CB. Our new dating results are integrated with a compilation of regional low-temperature thermochronological data to determine the CB evolution in a tectonic and topographic evolution framework. Zircon and apatite (U-Th)/He central ages of the eight granitoids range from 146 to 30 and 82 to 31 Ma, respectively, implying a long-lasting exhumation of the intracontinental CB. Inverse thermal modeling of the thermochronological data for the eight plutons indicates that the intracontinental CB underwent three exhumation phases at 150-110, 110-85, and 66-38 Ma, of which the former two exhumation phases were prolonged and significant. A compilation of regional thermochronological data reveals a propagating locus of fast exhumation phase from the intracontinental CB to the seaward epicontinental CB over time. Combined with other geological evidence, we infer that primary exhumation events of the CB resulted from changing subduction processes of the Paleo-Pacific Plate, which include slab break-off and foundering in the Late Jurassic, progressive slab retreat in the Early Cretaceous, and normal subduction in the Late Cretaceous, with minor exhumation events presumably triggered by the Paleogene opening of the South China Sea Basin.