HR: 1340h
AN: T23C-1543    [Abstracts]
TI: Isotopic and Thermochronological Evidence for Origin and Erosion History of the Gamburtsev Mountains, East Antarctica
AU: * Cox, S E
EM: sec2125@columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964, United States
AU: Hemming, S R
EM: sidney@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964, United States
AU: Reiners, P W
EM: reiners@u.arizona.edu
AF: Department of Geosciences, University of Arizona, 1040 E 4th St., Tucson, AZ 85721, United States
AU: Nicolescu, S
EM: stefann@u.arizona.edu
AF: Department of Geosciences, University of Arizona, 1040 E 4th St., Tucson, AZ 85721, United States
AU: Thomson, S N
EM: stuart.thomson@yale.edu
AF: Department of Geology & Geophysics, Yale University, PO Box 201809, New Haven, CT 06520-8109, United States
AU: Gehrels, G E
EM: ggehrels@u.arizona.edu
AF: Department of Geosciences, University of Arizona, 1040 E 4th St., Tucson, AZ 85721, United States
AU: Gehrels, G E
EM: ggehrels@u.arizona.edu
AF: Department of Geology & Geophysics, Yale University, PO Box 201809, New Haven, CT 06520-8109, United States
AU: van de Flierdt, T
EM: tina@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964, United States
AU: van de Flierdt, T
EM: tina@ldeo.columbia.edu
AF: Department of Geology & Geophysics, Yale University, PO Box 201809, New Haven, CT 06520-8109, United States
AU: Goldstein, S L
EM: steveg@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964, United States
AU: Brachfeld, S A
EM: brachfelds@mail.montclair.edu
AF: Department of Earth and Environmental Studies, Montclair State University, 1 Normal Avenue, Montclair, NJ 07043, United States
AB: The Gamburtsev Subglacial Mountains (GSM) in East Antarctica are located near the South Pole of Inaccessibility and are covered by 0.6-4 km of ice. Their ice-free elevation is approximately 2 km, and they are considered enigmatic due to their great elevation in the center of a continent that is surrounded by passive rift margins. Understanding the origin and erosion history of these mountains is important for constraining the tectonic history of East Antarctica. Additionally, these mountains are considered one of the key postulated source points for development of post-Eocene glaciation. However, they have not yet been sampled directly because there are no outcrops. Topography and ice flow suggest that terrigenous sediment to the Lambert Graben-Prydz Bay Basin were derived from flow paths consistent with drainage from the GSM. We have taken sediment samples from young glacial diamict (from NBP01-01 JPC34) and from Eocene fluvial-deltaic sediments (ODP-1166A) in order to evaluate their provenance, with the goal of constraining the origin and uplift history of the GSM. In particular the Eocene fluvial-deltaic sediments should have received a significant fraction of their detritus from the GSM. For both sample types, zircon (U-Th)/Pb ages are dominated by ca. 550 Ma ages, with a subordinate ca. 900 Ma peak and scattered older grains, while the ⁴⁰Ar/³⁹Ar ages of hornblende and biotite are ca. 500 and 490 Ma, respectively. The Nd isotope composition of the Eocene fluvial sediments are approximately 2 epsilon units higher than those of the Quaternary glacial sediments, but are not consistent with a substantially distinct source formation age or with a young volcanic source. In order to constrain the erosion history of these sediments, we measured (U-Th)/He ages on detrital apatite and zircon grains. The ages range from 110 to 316 Ma on detrital apatite and 197 to 397 Ma on detrital zircon (of pan- African (U-Th)/Pb age). Thermal models that fit the mineral ages suggest rapid uplift and erosion in pan-African times followed by gradual erosion since about 490 Ma of ~10-18 km of crust (~.02-.04 km/Ma). Collectively, if the assumption holds that the sediments were derived from the GSM, then the crust that forms them has an average mantle extraction age of ca. 2 Ga, and experienced major tectonothermal reworking during pan-African orogenesis. Although more data are clearly needed to make a firm conclusion, the rapid, recent exhumation that would be expected if these mountains were young and quickly eroding was not observed.
DE: 1051 Sedimentary geochemistry
DE: 1099 General or miscellaneous
DE: 1115 Radioisotope geochronology
DE: 1140 Thermochronology
DE: 1165 Sedimentary geochronology
SC: Tectonophysics [T]
MN: 2007 Fall Meeting