HR: 0800h
AN: T11A-1243    [Abstracts]
TI: Provenance of Glaciomarine Sediments in the Circum-Antarctic Oceans: Implications for Geological History of Bedrock Sources and Sediment Dispersal
AU: * Roy, M
EM: mroy@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: van de Flierdt, T
EM: tina@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Hemming, S R
EM: sidney@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AU: Goldstein, S L
EM: steveg@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964 United States
AB: The Antarctic ice sheet covers a large fraction of the Antarctic continent thereby preventing a detailed study of the underlying basement rocks. Although the main geological divisions of Antarctica are reasonably well understood, more information is needed on the bedrock geology in order to better constrain the sources of sediments originating from Antarctica, and secondly, to characterize the dispersal of sediments entering the circum-polar oceans. Here we present the radiogenic (Nd and Sr) isotope composition of the $<$63 um terrigenous sediment fraction as well as $^{40}$Ar/$^{39}$Ar ages of individual hornblende grains taken from the $>$150 um fractions of core-top samples from a series of deep-sea cores that are located around the perimeter of the Antarctic continent (latitude $\sim$65$\deg$øS). The sediments are glaciogenic in origin and likely derive from the glacial erosion by ice streams that are fed by tributaries that drain the deep interior of the continent. The sediment samples should thus represent the variety of bedrock lithologies underlying the different sectors of the ice sheet. The results show a geographic variability of Nd and Sr isotope compositions that reflects the large age-range of basement domains of Antarctica. For instance, samples with radiogenic Nd and unradiogenic Sr near the Antarctic Peninsula are concordant with the recent volcanics and Mesozoic rocks of this region ($\epsilon$Nd: -1 to -3; $^{87}$Sr/$^{86}$Sr: 0.7068-0.7078), while samples with highly unradiogenic Nd and radiogenic Sr around the East Antarctic region reflect the presence of basement rocks with Archean and Proterozoic heritage (ex.: Amery Ice Shelf sector, $\epsilon$Nd: -17 to -21; $^{87}$Sr/$^{86}$Sr: 0.7046-0.7077). Samples from West Antarctica and the Antarctic Peninsula yield hornblende $^{40}$Ar/$^{39}$Ar ages $<$200 Ma, in agreement with the surficial bedrock geology of this sector and the Nd and Sr isotope data. In contrast, the $^{40}$Ar/$^{39}$Ar hornblende ages from samples of the eastern sector have a dominant population of grains with ages of $\sim$~500 Ma. We interpret this observation to imply that an important episode of metamorphism, approximately the age of the Ross Orogen, affected a large fraction of the terrains of East Antarctica. These results provide new information on the sediment sources around Antarctica, which will aid in the identification of the sectors of the Antarctic ice sheet that contribute to ice rafted detritus in the marine environment of the circumpolar region. Additionally, the discovery of a very broad zone of 500 Ma metamorphism indicates the power of sedimentary provenance studies for better understanding the geology of this continent.
DE: 4825 Geochemistry
DE: 3022 Marine sediments--processes and transport
DE: 1040 Isotopic composition/chemistry
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting