HR: 14:00h
AN: V53D-02    [Abstracts]
TI: Understanding the Magmatic Construction of the Dufek Complex, Antarctica
AU: * Cheadle, M J
EM: cheadle@uwyo.edu
AF: Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071,
AU: Meurer, W P
EM: william.p.meurer@exxonmobil.com
AF: ExxonMobil Upstream Research Co., P. O. Box 2189, Houston, TX 77252-2189,
AU: Grimes, C B
EM: cgrimes@uwyo.edu
AF: Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071,
AU: Gee, J S
EM: jsgee@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD, La Jolla, CA 920930220,
AU: McCullough, B C
EM: talkeetnaproduction@alaska.net
AF: 11 Freedom Drive, PO Box 274, Talkeetna, AK 99676,
AB: The Jurassic (~180Ma) Dufex Complex in the Pensacola Mountains of Antarctica is arguably one of the largest layered mafic intrusions in the world, with a minimum areal extent of 6600km². It is mostly buried beneath the Antarctic Icesheet, but is exposed in two parallel mountain ranges; the 45km long Dufek Massif and the 85km long Forrestal Range, which have exposed stratigraphic thicknesses of ~1.8 km and ~1.7 km respectively (Ford, 1976). The two sections appear to be petrologically related, showing a continuous differentiation trend; although some geophysical studies suggest they may represent separate intrusive events (Ferris et al., 1998). The Dufek Massif section consists of the ~230m thick Walker Anothosite unit overlain by the 1550m thick Augenbaugh Gabbro unit. The bottom of the intrusion is not exposed, although geophysical data suggest the presence of an ultramafic basal unit. In the Antarctic summer of 2006/07, we collected and logged 630 oriented rock cores from the lowermost 600m of the section producing a revised and more detailed stratigraphy for this part of the intrusion. In particular, we re-located the boundary between the Walker Anorthosite upwards, so that the Lower Anorthosite of the Augenbaugh Gabbro unit becomes the top of the Walker Anorthosite. We also collected and logged an additional 210 cores from a 100m section higher in the Augenbaugh Gabbro unit. Magnetic susceptibility variation with height was used to correlate between stratigraphic sections. The Walker Anorthosite consists of ortho- and clinopyroxene-bearing spotted anorthosites, interbedded on the meter scale with norites and layered gabbronorites. Modal plagioclase exceeds 65%. Slumped horizons a few meters thick are common, demonstrating a lack of stability of the accumulating mush. The lower part of the Augenbaugh Gabbro unit consists of massive and weakly banded gabbronorites with both cumulus pyroxene and plagioclase, and modal plagioclase ranging from 55- 65%. Rare, thin (<1-2m) anorthosite layers occur as do occasional pyroxenite horizons varying from a few tens of centimeters to several meters thick. The pyroxenite horizons tend to have modally sharp bottoms and gradational tops and may indicate, and constrain the volume of, replenishment events. Large orthopyroxene oikiocrysts (4-20+cm) are common throughout the Augenbaugh gabbro. Horizons of mafic volcanic and calc silicate sedimentary xenoliths ranging in size from 5cm to 5m are present at several levels within the sequence. Pegmatoids and other evidence of volatile enrichment are extremely rare. Our study aims to combine geochemical and textural studies together with magnetic remanence and fabric studies to determine the constructional and thermal history of the lower part of the Dufek Intrusion.
DE: 1518 Magnetic fabrics and anisotropy
DE: 3618 Magma chamber processes (1036)
DE: 3643 Layered magma chambers
DE: 3690 Field relationships (1090, 8486)
DE: 9310 Antarctica (4207)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting