McFadden, R., Siddoway, C.S., Teyssier, C., Fanning, C.M., and Kruckenberg, S.C.
In: Antarctica: A Keystone in a Changing World-Online Proceedings of the 10th ISAES, edited by AK Cooper and CR Raymond et al. USGS Open-File Report 2007-1047; Short Research Paper 046P: 6 p. doi: 103133/of2007-1047.srp046
Publication year: 2007


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 across the south flank of the dome, and a mylonitic shear zone mapped for 30 km between Mt. Iphigene and Mt Richardson. 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 meltpresent deformation age, and a U-Pb age of 96 Ma, from a crosscutting granitic dike, gives a lower age limit for deformation. The shear zone, 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.