GEOCHEMISTRY OF JURASSIC DOLERITE INTRUSIONS IN THE UPPER TAYLOR GLACIER REGION, SOUTH VICTORIA LAND, ANTARCTICA

Jurassic tholeiites of the Ferrar Large Igneous Province (FLIP) crop out in a linear belt that extends for over 3000 km along the Transantarctic Mountains. 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 along the base of and within flat-lying Devonian to Triassic supracrustal strata of the Beacon Supergroup. No regionally extensive dike swarm has been identified within the province and a number of possible magma transport models have been proposed. We are currently in the process of conducting an integrated structural, petrofabric, and paleomagnetic study aimed at establishing magma flow directions in intrusions from the upper Taylor Glacier region in order to further constrain models of emplacement. To provide context for the flow direction data we have used chemistry to assist in developing a geometric framework and chronology in the Ferrar intrusive complex. On a local scale, distinctive chemical compositions of the intrusions can be used to provide a chemical “fingerprint” that is useful for correlation of otherwise indistinguishable dolerites. Major and trace element analysis from chilled margins of intrusions from the upper Taylor Glacier region fall into two distinct compositional groups. One group has chemical compositions that tightly cluster around MgO=4.3%, TiO2=1.0%, Zr=165 ppm. This group includes the regionally extensive Peneplain Sill that crops out north of the Taylor Glacier and several stratigraphically higher sills in the eastern Quartermain Mountains. A second group displays a range of distinctly more mafic compositions: MgO=5.4 - 6.9%, TiO2=0.64 - 0.71%, Zr=101-118 ppm. This group includes the regionally extensive Basement Sill north of the Taylor Glacier and a sequence of dikes in the southeastern Quartermain Mountains. We interpret these two groups to represent at least two chemically distinct pulses of magma. Well documented crosscutting relationships between the dikes and sills in the Quartermain Mountains provide evidence that at least some of the intrusions in the more mafic group are distinctly younger.