U-Th-Pb monazite and Sm-Nd dating of high-grade rocks from the Grove Mountains, East Antarctica： further evidence for a Pan-African-aged monometamorphic terrane

摘要

cqvip:The Grove Mountains, 400 km south of the Chinese Antarctic Zhongshan Station, are an inland continuation of the Pan-African-aged (i.e., Late Neoproterozoic/Cambrian) Prydz Belt, East Antarctica. In this paper we carried out a combined U-Th-Pb monazite and Sm-Nd mineral-whole-rock dating on para-and orthogneisses from bedrock in the Grove Mountains. U-Th-Pb monazite dating of a cordierite-bearing pelitic paragneiss yields ages of 523 ± 4 Ma for the cores and 508 ± 6 Ma for the rims. Sm-Nd mineral-whole-rock isotopic analyses yield isochron ages of 536 ± 3 Ma for a coarse-grained felsic orthogneiss and 507 ± 30 Ma for a fine-grained quartzofeldspathic paragneiss. Combined with previously published age data in the Grove Mountains and adjacent areas, the older age of ～530 Ma is interpreted as the time of regional medium-to low-pressure granulite-facies metamorphism, and the younger age of ～510 Ma as the cooling age of the granulite terrane. The absence of evidence for a Grenville-aged (i.e., Late Mesoproterozoic/Early Neoproterozoic) metamorphic event indicates that the Grove Mountains have experienced only a single metamorphic cycle, i.e., Pan-African-aged, which distinguishes them from other polymetamorphic terranes in the Prydz Belt. This will provide important constraints on the controversial nature of the Prydz Belt.