New age constraints for a short pulse in Ross orogen deformation triggered by East-West Gondwana suturing

Constraints on the timing of deformation within the Antarctic Ross orogenic belt are important for understanding early Paleozoic tectonic activity accompanying the assembly of Gondwana. One of the best areas for constraining the tectonic evolution of the Ross orogenic belt is the Holyoake Range in the central Transantarctic Mountains where previous work shows an abrupt change in the stratigraphic succession of the Cambrian Byrd Group possibly related to the inception of tectonism within the orogen at similar to 515 Ma. To further constrain deformational timing, we conducted 40Ar-39Ar analyses on magmatic phases of the Holyoake Gabbro, which cross-cuts folded Lower Cambrian Shackleton Limestone of the Byrd Group. Our analyses yield average ages of 506.7 +/- 3.6 Ma (2 sigma; MSWD=0.9) and 504.1 +/- 2.4 Ma (2 sigma; MSWD=1.3) for hornblende from the early and late magmatic phases, respectively. Deformation of the Shackleton Limestone therefore occurred prior to 506.7 3.6 Ma, which is similar to 12 m.y. after the siliciclastic drowning of the carbonate platfonn inferred to record the start of Ross tectonism in the central Transantarctic Mountains. On a regional scale, the data are consistent with a short pulse of deformation, which was probably related to global plate motion changes following final suturing of East and West Gondwana. (c) 2007 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.