Exhumation history of late Mesozoic intrusions in the Tongling–Xuancheng area of the Lower Yangtze region, eastern China: Evidence from zircon (U–Th)/He and apatite fission track thermochronology

Abstract

The Lower Yangtze region is one of the most important metallogenic belts in eastern China, yet there are few precise low-temperature geochronological data to constrain the evolution of the orefield. We collected samples from 12 late Mesozoic intrusions in the Tongling–Xuancheng area for zircon (U–Th)/He (ZHe) and apatite fission track (AFT) dating. These intrusions are divided into early and late periods on the basis of their emplacement ages. The ZHe and AFT ages of the early intrusions are 144.6–111.0 Ma and 123.1–89.4 Ma, respectively, and those of the late intrusions are 119.9–71.3 Ma and 96.7–66.9 Ma, respectively, with rare outliers. The ZHe and AFT age distributions and the modeled low-temperature thermal histories of these intrusions reveal that the Tongling–Xuancheng area underwent three stages of rapid cooling: during the earliest, middle, and end of the Early Cretaceous. During the earliest Early Cretaceous, rapid cooling resulted from regional compression and in situ cooling of magma. The middle Early Cretaceous phase of cooling occurred in a regional extensional regime characterized by the development of large rift basins and the emplacement of intrusions. The rapid cooling at ~ 100 Ma was concurrent with a global plate reorganization event that resulted in regional basin inversion and the development of unconformities between the Lower and Upper Cretaceous strata in East Asia. Although Cenozoic uplift is not seen in the cooling paths of our samples, regional compression since the Paleogene has uplifted the orebodies to near-surface level, favoring ore exploration and mining.