Friday, 31 August 2007 - 1:30 PM
5.P1.B-1
Cretaceous oblique detachment tectonics in the Fosdick Mountains, Marie Byrd Land, Antarctica
Rory McFadden1, Christine Smith Siddoway2, Christian Teyssier1, C.M. Fanning3, and Seth C. Kruckenberg1. (1) Department of Geology and Geophysics, University of Minnesota, 310 Pillsbury Drive SE, Minneapolis, MN 55455, (2) Department of Geology, The Colorado College, 14 E. Cache la Poudre, Colorado Springs, CO 80903, (3) Research School of Earth Sciences, Australian National University, Canberra, ACT 2000, Australia
The Fosdick Mountains form an E-W trending migmatite dome in the northern Ford Ranges of Marie Byrd Land, Antarctica. Pervasively folded migmatites derived from lower Paleozoic greywacke and middle Paleozoic plutonic rocks constitute the dome. New field research documents a transition from melt-present to solid-state deformation upon the south flank of the dome, and a throughgoing mylonitic shear zone mapped for 10 km between Mt Richardson and Mt Getz. Kinematic shear sense is dextral normal oblique, with top-to-the-SW and -WSW transport. A U-Pb age of 107 Ma, from a leucosome-filled extensional shear band, provides a melt-present deformation age, and a U-Pb age of 96 Ma, from a crosscutting granitic dike, gives a lower age limit for deformation. The structure, here named the South Fosdick detachment zone, forms the south flank of the migmatite dome and was in part responsible for the exhumation of mid-crustal rocks.