Zircon U-Pb and Hf isotopic study for the migmatised amphibolites in the Cathaysia Block: implications on the granulite facies metamorphism of Caledonian event in Southeastern China

Amphibolites occur in a number of localities in the Cathaysia Block, and their protoliths represent basaltic magmas erupted in various tectonic settings. Cathodoluminescence images show that zircons from the representative amphibolites have unzoned or sector-zoned structure. LA-ICP-MS analysis indicates that most zircons have low Th/U ratios and four amphibolites yield U-Pb zircon ages of 446 ± 5, 435 ± 2, 434 ± 4 and 423 ± 2 Ma, respectively. Lu-Hf isotopic analysis on these zircons gives Hf model ages ranging from 900 Ma to 1200 Ma. In combination with lithological observations and previously published geochronological data, we interpret that these U-Pb ages record an important granulite-facies metamorphic event that led to migmatization and low-degree of partial melting. This Caledonian tectonothermal event in the Southeastern China has a great tectonic implication for the evolutionary history of the Cathaysia Block. This research is financially supported by Hong Kong Research Grant Council (HKU 7041/05).