Structure and timing of transpressional deformation in the Shackleton Glacier area, Ross orogen, Antarctica

Abstract

Basement of the Transantarctic Mountains comprises the Ross orogenic belt, a Neoproterozoic to Ordovician mobile belt located along the palaeo-Pacific margin of Gondwana. Our structural analysis of deformation in the Liv Group, a sequence of Cambrian volcanic, volcaniclastic, clastic and carbonate rocks, and nearby plutonic rocks indicates that the Shackleton Glacier area has a polyphase deformation history that includes development of both contractional and strike-slip structures. We describe evidence for synchronous contraction and strike-slip movement, and suggest that the structural suite in this area developed, at least in part, within a sinistral transpressive kinematic regime. Deformation in the Shackleton Glacier area is inferred to be at least in part younger than 505 Ma, based on the deformation of the well-dated Taylor Formation. New 40 Ar/ 39 Ar cooling ages from metamorphosed igneous and sedimentary rocks range from c. 500 to 470 Ma and are interpreted to date orogenic cooling. Based on our structural results, and on consideration of the tectonic environment represented by the Liv Group, we propose that shortening across a subduction-related volcanic arc system caused deformation of the Liv Group and associated plutonic rocks. Oblique convergence and thus, transpression, may have ultimately been related to left-oblique plate subduction.

Geometrical analysis of structural data collected at high South latitude: A modular arithmetic method that addresses meridional convergence

“…The ~45° variation in trend is comparable to that observed in the central Transantarctic Mountains at tectonic boundaries such as Byrd Glacier (Paulsen et al 2004: Figure 1b). The angular difference in orientation may be an expression of localized collisional stages along the Gondwana margin (e.g.…”

“…The Pensacola, Ellsworth-Whitmore, and southern Transantarctic Mountains experienced contractional to transpressional deformation during the Middle Cambrian Ross Orogeny (Curtis et al 2004;Paulsen et al 2004;Duebendorfer and Rees, 1998) or later (Curtis 2001). Folds and cleavage developed in argillite, phyllite, and volcanic rocks existing at all three sites, together with strike slip faults and shear zones.…”

“…Structural data reported in the literature are presented in standard equal area stereographic plots and referenced to longitudes of 184° East (176°W) for the southern Transantarctic Mountains (e.g. Paulsen et al 2004), to 274° East (086°W) for the Ellsworth Mountains (e.g. Curtis 2001;Spörli and Craddock, 1992), and to 305° (055°W) for the Pensacola range (e.g.…”

“…The aim of the analysis is to demonstrate the effectiveness of the approach by assessing the along-strike geometry of structural elements in the Ross orogenic belt and examining the geometrical and kinematic relationships between transpressive and wrench elements (e.g. Curtis et al 2004;Paulsen et al 2004) of the orogen. The analysis also offers the means to evaluate the 90° counterclockwise rotation of the Ellsworth Mountains block during Weddell Sea opening determined from paleomagnetic data (Figure 1; Grunow et al, 1991) and to examine whether geometrical evidence from rock fabrics has any bearing on the controversy over timing of tectonism in the Ellsworth Mountains (Curtis, 1998;Duebendorfer and Rees, 1998).…”

“…A comparison of the Pensacola and southern TAM data show that the planar and linear D1-D2 fabrics differ in orientation by ~45° (Figure 2d-e), despite the fact that both exist in a progression of textures that record compression to sinistral transpression (Paulsen et al, 2004;Curtis et al, 2004), during Middle Cambrian Ross tectonism. The ~45° variation in trend is comparable to that observed in the central Transantarctic Mountains at tectonic boundaries such as Byrd Glacier (Paulsen et al 2004: Figure 1b).…”