Neoarchean-Early Paleoproterozoic and Early Neoproterozoic arc magmatism in the Ltitzow-Holm Complex, East Antarctica: Insights from petrology, geochemistry, zircon U-Pb geochronology and Lu-Hf isotopes

摘要

The Ltitzow-Holm Complex (LHC) of East Antarctica forms part of the Neoproterozoic-Cambrian high-grade metamorphic segment of the East African-Antarctic Orogen. Here we present new petrological, geochemical, and zircon U-Pb and Lu-Hf isotopic data for meta-igneous rocks including chamockite, felsic gneiss, metagabbro, and mafic granulite from the LHC and evaluate the Neoarchean to Early Paleoproterozoic (ca. 2.5 Ga) and Early Neoproterozoic (ca. 1.0 Ga) arc magmatic events. The trace element geochemical signatures reveal a volcanic arc affinity for the charnockites from Sudare Rocks and Vesleknausen and felsic gneiss from Rundvagshetta, suggesting that the protoliths of these rocks were derived from felsic arc magmas. In contrast, metagabbros from Skallevikshalsen and Austhovde, occurring as boudins in metasediments, show non-arc signatures (within plate basalt or mid-oceanic ridge basalt). The upper intercept ages of magmatic zircons in charnockite plotted on concordia diagrams yielded 2508 +/- 14 Ma (Sudare Rocks) and 2490 +/- 18 Ma (Vesleknausen), clearly suggesting a Neoarchean to Early Paleoproterozoic arc magmatic event. A subsequent thermal event during Early Neoproterozoic traced by Pb-206/U-238 age of oscillatory-zoned core of zircon in mafic granulite from Langhovde (973 10 Ma) is consistent with a similar Early Neoproterozoic magmatic event reported from the LHC, suggesting a second stage of arc magmatism. The timing of peak metamorphism has been inferred from Pb-206/U-238 mean ages of structureless zircons in metagabbros from Skallevikshalsen and Austhovde, mafic granulite from Langhovde, and felsic gneiss from RundvAgshetta in the range of 551 +/- 5.4 to 584 +/- 5.0 Ma. Zircon Lu-Hf data of Neoarchean charnockites from Sudare Rocks and Vesleknausen indicate that the protolith magma was sourced from Paleo-to Neoarchean juvenile components mixed with reworked ancient crustal materials. Protolith magmatic rock of the felsic gneiss from Rundvagshetta might have been sourced from reworked Paleoarchean crust. In contrast, metagabbros from Skallevikshalsen and Austhovde were derived from the Paleoproterozoic reworked crust. The results of this study suggest the occurrence of several discrete crustal fragments of ca. 2.5 Ga and ca. 1.0 Ga juvenile magmatic arcs in the southwestern part of the LHC, which amalgamated during the latest Neoproterozoic collisional event related to the final stage of assembly of the Gondwana supercontinent (C) 2016 Elsevier B.V. All rights reserved.