Ar-40/Ar-39 ages of hornblende grains and bulk Sm/Nd isotopes of circum-Antarctic glacio-marine sediments: Implications for sediment provenance in the Southern Ocean

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Chemical Geology
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Oct 15
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The transfer of terrigenous sediments from Antarctica to the Southern Ocean results from glaciological processes and subsequent transport by ocean cur-rents. Establishing the link between the composition of circumpolar sediments and the geology of Antarctica can provide important insights into past ice sheet and ocean current dynamics. Here we document the variability of Antarctic sediment sources using Ar-40/Ar-39 ages of individual detrital hornblende grains and bulk (<63 m) Sm/Nd isotope systematics from glacio-marine sediments from 29 cores surrounding Antarctica. High Nd-143/Nd-144 ratios and associated young Sm/Nd-model ages characterize sediments proximal to West Antarctica, while lower Nd-143/Nd-144 ratios and correspondingly older Sm/Nd-model ages are found in samples nearby East Antarctica. Detrital hornblende grains in West Antarctic sediments typically have Ar-40/Ar-39 ages younger than 200 Ma while East Antarctic hornblende grains yield 40Ar/39Ar ages that cluster in a predominant population centered on similar to 500 Ma, reflecting the widespread late Neoproterozoic-early Cambrian (Pan-African and Ross) orogenies that affected East Antarctica. An exception comes from sediments adjacent to Wilkes Land, where abundant Mesoproterozoic and Paleoproterozoic hornblende grains suggest that this portion of the East Antarctic craton was largely buffered from Pan-African metamorphism. The geochemical characteristics of sediment sources are thus consistent with the geology of rock outcrops around the Antarctic perimeter. The combined Sm-Nd data and Ar-40/Ar-39 ages of circum-Antarctic glacio-marine sediments outline several geographic sectors with distinct provenance signals, thereby providing a base map for fingerprinting sediment sources from the Antarctic margin. (C) 2007 Elsevier B.V All rights reserved.


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DOI 10.1016/j.chemgeo.2007.07.017