Phanerozoic Metamorphic Episodes and Characteristics of Cathaysia Block

There were several episodes of metamorphism in the Cathaysia Block. The Caledonian metamorphism occurred over the most area, and the highest grade was up to granulite facies. The granulites scatter over the Cathaysia Block with NE direction parallel to orogeny belt. It is proposed that the metamorphism took place in the orogenic setting, which likely resulted from the assembling and colliding of the Yangtze Block to the northern Gondwanaland, leading to deformation and metamorphism of sediments in the passive continental margin of the northern Gondwanaland. According to LA ICP-MS zircon U-Pb dating results of the Meixian gneiss and Xingning migmatite in eastern Guangdong Province and geochronological data of the monazites from nearby metamorphic rocks, the Hercynian metamorphism in the Cathaysia Block mainly took place at 260～280 Ma, younger than the typical Hercynian orogeny event in the central European continent. The Hercynian metamorphism in the Cathaysia Block was locally distributed, and probably occurred under the extension setting. The Indosinian metamorphism was wider in the Cathaysia Block, and the metamorphic grade in the Darongshan-Shiwandashan area at southwestern Cathaysia might reach granulite facies. The metamorphism in other regions was characterized by middle-low pressure faceis series, which might be related with the extension setting in late Indosinian orogeny. LA ICP-MS zircon U-Pb isotope analyses indicate that the Indosinian metamorphism in the central Cathaysia occurred at 231～232 Ma. The Yanshanian metamorphic rocks, which are distributed along the coastal area of southeastern China and Central Range of Taiwan, show the feature of paired metamorphic belts. It probably suggests that the metamorphism be closely related with the subduction of Pacific Ocean under the southeastern China. The directions of metamorphic belt were different from Indosinian to Yanshanian events, indicating that tectonic regime influencing the Cathaysia Block was transformed in these two episodes.