HR: 16:15h
AN: V14C-02    [Abstracts]
TI: Geographic Variations in Chilled Margin Chemistry of Jurassic Dolerite Intrusions in the Dry Valley Region of South Victoria Land, Antarctica
AU: * Fleming, T H
EM: flemingt1@southernct.edu
AF: Department of Earth Science, Southern Connecticut State University, 501 Crescent Street, New Haven, CT 06515
AU: Elliot, D H
EM: elliot.1@osu.edu
AF: Department of Geological Sciences, Ohio State University, 125 South Oval Mall, Columbus, OH 43210
AU: Calhoun, A
EM: acalhoun@mac.com
AF: Department of Earth Science, Southern Connecticut State University, 501 Crescent Street, New Haven, CT 06515
AB: Jurassic tholeiites of the Ferrar Large Igneous Province (FLIP) crop out in a linear belt that extends for over 3000 km along the Transantarctic Mtns. The FLIP was emplaced over a short period of time (<1 m.y.) and is temporally associated with the initiation of Gondwana break-up in the Weddell Sea sector of Antarctica. The intrusive phase of the FLIP consists primarily of a high level complex of dolerite sills and subordinate connecting and cross-cutting dikes that have intruded near the base of and within flat-lying Devonian to Triassic supracrustal strata of the Beacon Supergroup. In the Dry Valley region of south Victoria Land (SVL), the two most prominent sills are intruded along (peneplain sill) and just below (basement sill) the regional unconformity. Geologic mapping has commonly assumed that each of these intrusions is regionally extensive in SVL at roughly the same stratigraphic level. No extensive dike swarm has been identified within the province to act as a feeder for these sills and a number of possible magma transport models have been proposed. During the 2004-05 Magmatic Field Laboratory Workshop, chilled margin samples of dolerite intrusions were systematically collected from localities in the Wright and Victoria Valleys adjacent to Bull Pass. The major and trace element composition of samples from the basement sill in this region tightly cluster around a single composition (SiO₂=55.0%, MgO=6.8%, TiO₂=0.63%, Zr=100 ppm) despite a geographic spread of ~16 km. Two chilled margin samples collected from the Peneplain sill in the same region have identical chemical compositions to the basement sill. In contrast, prior work on chilled margins of intrusions from the upper Taylor Glacier region fall into three distinctly different compositional groups. The basement sill in the Taylor Glacier region has slightly more evolved compositions (SiO₂=55.7%, MgO=5.6%, TiO₂=0.71%, Zr=117 ppm) than in the region surrounding Bull Pass. The peneplain sill and several stratigraphically higher sills in the eastern Quartermain Mtns have significantly more evolved chemical compositions that cluster around SiO₂=57.5%, MgO=4.3%, TiO₂=1.0%, Zr=165 ppm. A sequence of dikes in the southeastern Quartermain Mtns that cross cut sills in that region have compositions similar to the basement and peneplain sills in the Bull Pass region. The complete suite of compositions from both regions can be easily related by simple low-pressure gabbro fractionation. Existing correlations between the Taylor Valley and Bull Pass region requires extrapolation through the poorly exposed and largely ice covered Asgard Range (~15 km). Differences in the compositions of the basement and peneplain sills in each region hint at the possibility that they may be different intrusions. Alternatively, if the existing correlations are correct, our results document a trend of increasingly more evolved chilled margin compositions to the south in both the basement and peneplain sills. If the chilled margins of sills become more evolved away from their initial filling conduit as a result of differentiation processes operating during emplacement, the observed chemical trends would be consistent with a source located in the direction of the Bull Pass region as proposed by Marsh (2004). Marsh, B. (2004) A Magmatic Mush Column Rosetta Stone: the McMurdo Dry Valleys of Antarctica, EOS, 85(47) 497-508.
DE: 1065 Major and trace element geochemistry
DE: 3640 Igneous petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005