Tong, Laixi and Liu, Zhao and Li, Chao and Lu, Junsheng and Yang, Wenqiang and Wang, Yanbin
(2024)
Polymetamorphism of the ultrahigh-temperature granulites in the Rauer Group, East Antarctica: new evidence from zircon SHRIMP U-Pb ages.
Advances in Polar Science, 35 (2).
pp. 192-205.
Abstract
The Rauer Group is located on the eastern margin of the early Paleozoic Prydz Belt in East Antarctica, and the typical ultrahigh-temperature (UHT, >900 ℃) granulites outcrop on Mather Peninsula. However, the timing of UHT metamorphism and P–T path of the UHT granulites have long been debated, which is critical to understanding the tectonic nature and evolution history of the Prydz Belt. Thus, both a sapphirine-bearing UHT metapelitic granulite and a garnet-bearing UHT mafic granulite are selected for zircon SHRIMP U-Pb age dating. The results show that metamorphic zircon mantles yield weighted mean 206Pb/238U ages of 918±29 Ma and 901±29 Ma for the metapelitic and mafic granulites, respectively, while zircon rims and newly grown zircons yield weighted mean 206Pb/238U ages of 523±9 Ma and 532±11 Ma, respectively. These new zircon age data suggest that the UHT granulites may have experienced polymetamorphism, in which pre-peak prograde stage occurred in the early Neoproterozoic Grenvillian orogenesis (1000–900 Ma), whereas the UHT metamorphism occurred in the late Neoproterozoic to early Paleozoic Pan-African orogenesis (580–460 Ma). This implies that P–T path of the UHT granulites should consist of two separate high-grade metamorphic events including the Grenvillian and Pan-African events, which are supposed to be related to assembly of Rodinia and Gondwana supercontinents respectively, and hence the overprinting UHT metamorphic event may actually reflect an important intracontinental reworking.
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