阿帕拉契北部阿克殿造山運動之地體構造－岩漿演化研究

The Acadian Orogeny of the Northern Appalachians was caused by accretion of the peri-Gondwanan terranes Avalonia and Meguma to the eastern margin of Laurentia during the Devonian. The geological relationship between Avalonia and Meguma prior to accretion is uncertain. Radioisotopic dating of detrital zircons from metasedimentary granulite xenoliths from the structural basement to the Meguma terrane indicate that Avalonia and Meguma were proximal and likely contiguous as they transited the Rheic Ocean. The zircon ages range from the Late Silurian to Cryogenian with minor Mesoproterozoic and Paleoproterozoic peaks. Furthermore, three distinct metamorphic events are identified at ~400 Ma, ~375 Ma, and ~355 Ma. We conclude that the granulite facies metamorphism experienced by the metasedimentary rocks occurred as the Meguma terrane overthrust Avalonia 10-20 million years after deposition of their protolith whereas the younger events are related to post-collisional processes. The implication is that Meguma and Avalonia jointly transited from Gondwana.