SHRIMP U-Pb zircon geochronology of high-grade rocks and charnockites from the eastern Amery Ice Shelf and southwestern Prydz Bay, East Antarctica: Constraints on Late Mesoproterozoic to Cambrian tectonothermal events related to supercontinent assembly

摘要

The eastern Amery Ice Shelf (EAIS) and southwestern Prydz Bay are situated near the junction between the Late Neoproterozoic/Cambrian high-grade complex of the Prydz Belt and the Early Neoproterozoic Rayner Complex. The area contains an important geological section for understanding the tectonic evolution of East Antarctica. SHRIMP U-Pb analyses on zircons of felsic orthogneisses and mafic granulites from the area indicate that their protoliths were emplaced during four episodes of ca. 1380 Ma, ca. 1210-1170 Ma, ca. 1130-1120 Ma and ca. 1060-1020 Ma. Subsequently, these rocks experienced two episodes of high-grade metamorphism at >970 Ma and ca. 930-900 Ma, and furthermore, most of them (except for some from the Munro Kerr Mountains and Reinbolt Hills) were subjected to high-grade metamorphic recrystallization at ca. 535 Ma. Two suites of charnockite, i.e. the Reinbolt and Jennings chamockites, intrude the Late Mesoproterozoic/Early Neoproterozoic and Late Neoproterozoic/Cambrian high-grade complexes at >955 Ma and 500 Ma, respectively. These, together with associated granites of similar ages, reflect late-to-post-orogenic magmatism occurring during the two major orogenic events. The similarity in age patterns suggests that the EAIS-Prydz Bay region may have suffered from the same high-grade tectonothermal evolution with the Rayner Complex and the Eastern Chats of India. Three segments might constitute a previously unified Late Mesoproterozoic/Early Neoproterozoic orogen that resulted from the long-term magmatic accretion from ca. 1380 to 1020 Ma and eventual collision before ca. 900 Ma between India and the western portion of East Antarctica. The Prydz Belt may have developed on the eastern margin of the Indo-Antarctica continental block, and the Late Neoproterozoic/Cambrian suture assembling Indo-Antarctica and Australo-Antarctica continental blocks should be located southeastwards of the EAIS-Prydz Bay region.