Sr and Nd Isotopic evidence in metacarbonate rocks for an extinct Island arc–ocean system in East Antarctica

Abstract

Chemically precipitated carbonate sediments directly record seawater composition that helps to decode the Earth's paleo-environment, the existence of paleo-oceans, and provide valuable clues on the paleo-tectonic position of continents through Earth's history. In addition, the geochemical and isotopic composition of carbonate rocks have a strong dependence on the depositional tectonic setting and surrounding source rock composition. This was particularly important in the Precambrian, during which biological activity was less prominent and vegetation was virtually absent. Here we present evidence for the existence of an extinct East Antarctic Ocean and its peripheral oceanic island arc system that preceded the formation of the East Antarctic continent in the Neoproterozoic before the final assembly of Gondwana. Applying a multi-element isotope geochemical approach on chemostratigraphically well-constrained metacarbonate rocks collected from the remote Sør Rondane Mountains in East Antarctica, we present a model on carbonate deposition surrounding an island arc system, mid-ocean volcanic islands and a shallow marine continental shelf of a yet unidentified interior Antarctic continent, all of which accreted in the late Neoproterozoic to early Paleozoic to form the present day East Antarctic continent prior to the final amalgamation of Gondwana supercontinent. Our results support the presence of an oceanic island arc system that might have separated the Mozambique ocean and East Antarctic ocean.

Prograde infiltration of Cl-rich fluid into the granulitic continental crust from a collision zone in East Antarctica (Perlebandet, Sør Rondane Mountains)

“…These low Sr isotope ratios can be attributed to interaction with low Sr-bearing magmatic fluids or to the older depositional age of Perlebandet metacarbonates compared to that from other parts of the SRM (Otsuji et al, 2013). Otsuji et al (2016) further pointed out that Nd and Sr isotopic data from metacarbonate rocks from Perlebandet neither match the data from the rocks in the SW terrane, nor from the Balchenfjella in the NE terrane. Based on these data, they proposed that Perlebandet carbonates were deposited in an environment surrounding an isolated seamount in the Tonian to Cryogenian period, and that amalgamation of Gondwana and the final closure of Mozambique Ocean and East Antarctic Ocean took place at ca.…”

“…Based on these data, they proposed that Perlebandet carbonates were deposited in an environment surrounding an isolated seamount in the Tonian to Cryogenian period, and that amalgamation of Gondwana and the final closure of Mozambique Ocean and East Antarctic Ocean took place at ca. 660-550 Ma (Otsuji et al, 2016).…”

“…Because the Mozambique Ocean is considered to have been located between the NE and SW terranes of the SRM before collision (Otsuji et al, 2016), sea water introduced into the depth and fluids released from the mantle are the likely candidates, and should be examined in future studies. High Cl content in biotite, hornblende and apatite is a measure of low log[f(H2O)/f(HCl)] of fluids, implying that the origin of Cl-rich fluids in the SRM can be also related to the magmatic activity during collision.…”

Multiple post-peak metamorphic fluid infiltrations in southern Perlebandet, Sør Rondane Mountains, East Antarctica

“…Based on Nd and Sr isotopic data, Perlebandet carbonates are proposed to have deposited in an environment surrounding an isolated seamount in the Tonian to Cryogenian period, and suggest that amalgamation of Gondwana and the final closure of Mozambique Ocean and East Antarctic Ocean took place at ca. 660-550 Ma (Otsuji et al, 2016). So far, all previous studies in Perlebandet reporting the P-T conditions, zircon U-Pb ages, CHIME monazite ages, and any isotope data dealt with samples collected from northern and central parts of Perlebandet (Asami et al, 2005;Shiraishi et al, 2008;Otsuji et al, 2013Otsuji et al, , 2016Kawakami et al, 2017).…”

“…660-550 Ma (Otsuji et al, 2016). So far, all previous studies in Perlebandet reporting the P-T conditions, zircon U-Pb ages, CHIME monazite ages, and any isotope data dealt with samples collected from northern and central parts of Perlebandet (Asami et al, 2005;Shiraishi et al, 2008;Otsuji et al, 2013Otsuji et al, , 2016Kawakami et al, 2017).…”