CHRONOLOGY OF THE INTRUSIVE ROCKS OF THE TONGLING AREA (ANHUI, CHINA) AND ITS TECTONIC SIGNIFICANCE

The crystallization ages of five intrusions from the Tongling area (Anhui, China) have been determined using zircon SHRIMP, which are the Xiaotongguanshan quartz monzodiorite(142.8±1.8Ma), the Fenghuangshan granodiorite(144.2±2.3Ma), the Shatanjiao quartz monzonite porphyry(151.8±2.6Ma), the Xinqiao monzonite(146.4±4.3Ma), and the Dongguashan pyroxene monzonite (148.2±3.1Ma). These data indicate that these intrusions are formed from 142.8 to 151.8Ma, which belong to the end of late Jurassic. South China is a region where the Pacific plate and the Eurasian plate have been interacting with each other since the Mesozoic. A post-Mesozoic change from the Tethyan tectonic domain, characterized by EW trending structures, to the western Pacific tectonic domain, characterized by NE and NNE trending structures, occurred in south China. The transformation started in the Indosinian epoch due to change in subduction angle of the paleo-Pacific plate. Most workers agree that the peak transformation occurred between Late Jurassic to Early Cretaceous, when the EW trending structures are transposed into NE and NNE trending structures. Thus, 145 Ma is generally considered to be an important time during the transformation, when the transformation resulted in widespread, sinistral NNE striking faults and magmatic belts. Based on our chronological results and regional deformation of the intrusions in the Tongling area, we accept this general tectonic evolution, but question the peak timing of transformation and that regional tectonism controlled pluton emplacement. Based on comparison of regional and emplacement deformation, it is suggested that the emplacement of these intrusions were not influenced by the NNE strike-slip faults, which are active during the cooling the pluton, causing the pluton and country rock offset. Therefore, the NNE strike-slip faults, representing the peak transformation from the Tethyan tectonic domain to the western Pacific tectonic domain, might occur after 142.8 ~ 151.8Ma regionally, corresponding to the post emplacement of the intrusions in the Tongling area.