Eocene Initiation of Ross Sea Dextral Faulting and Implications for East Antarctic Neotectonics
Rossetti, Federico, Storti, Fabrizio, Busetti, Martina, Lisker, Frank, et al., Journal of the Geological Society
The Ross Sea region of the East Antarctic plate provides evidence for intraplate tectonic activity in Cenozoic times. Still unresolved are the cause, timing and kinematics of this intraplate tectonism. By integrating and discussing the different (kinematic and temporal) signals of Cenozoic tectonism, intraplate dextral shearing is recognized as the main tectonic regime controlling the structural architecture of the Ross Sea region from the Mid-Eocene (c. 40-50 Ma) onward. We speculate that propagation and persistence of this tectonic regime through time constitutes a feasible seismogenetic framework to explain past and current tectonism in the Ross Sea region.
The Mesozoic-Cenozoic tectonic evolution of the Ross Sea region (namely Victoria Land and the Ross Sea; Figs 1 and 2) is dominated by the separation of the Antarctic continent from Australia and greater New Zealand and the development of the Ross Sea embayment (e.g. Stock & Cande 2002, and references therein). These events led to the development of two roughly orthogonal passive margins in the Southern Ocean and the Ross Sea, bounding the East Antarctic craton to the north and to the east, respectively (e.g. Lawver & Gahagan 1994; Sutherland 1999; Mukasa & Dalziel 2000; Stock & Cande 2002) (Fig. 1).
The post-break-up Cenozoic separation history is particularly complex and includes the transfer of continental blocks originally belonging to the Antarctic plate (Tasmania and South Tasmania Rise) to the Australia plate, through a diffuse transform boundary active until about Oligocene time (Stock & Cande 2002, and references therein).
The occurrence of Cenozoic intraplate deformation in the Southern Ocean and the Ross Sea regions has been recently proposed to reconcile global plate tectonics based on plate closure calculations (Cande et al. 2000) and models of global plate motions in the Pacific region (Steinberger et al. 2004). In particular, Steinberger et al. (2004) advocated a pre-Mid-Eocene, major intraplate dextral motion at the northeastern edge of the East Antarctic plate, whereas Cande et al. (2000) reconstructed a Cenozoic (from 43 to 26 Ma) rigid rotation between East and West Antarctica during the opening of the Adare Trough in the northwestern Ross Sea (Fig. 2). An increasing body of evidence, based on different datasets, attests that Cenozoic dextral intraplate shearing has affected both the Ross Sea and the Southern Ocean shoulders along NW-SE dextral fault systems, striking oblique to both passive margins, which can be traced from one margin to the other across the intervening continental lithosphere of Victoria Land (Salvini et al. 1997; Rossetti et al. 2003; Fig. 2). This tectonic regime is interpreted as responsible for the post 32 Ma transition from orthogonal to oblique rifting in the western Ross Sea (Salvini et al. 1997), and for magma production and emplacement of the Cenozoic McMurdo Magmatic Province along the western Ross Sea shoulder (Salvini et al. 1997; Rocchi et al. 2002). Additional supporting evidence for recent tectonic activity in the region comes from the occurrence of a low but significant level of seismic activity at the northeastern edge of the East Antarctica plate (Reading 2002: Fig. 1). In north Victoria Land, earthquakes seem to be localized along the Cenozoic, NW-SE-striking intraplate dextral fault systems or along strands emanating from them (Fig. 2). Furthermore, fossil seismic activity is recorded along the western Ross Sea shoulder, as indicated by the occurrence of pseudotachylyte-bearing fault cores distributed along the western margin of the Ross Sea (Fig. 2). The discovery of pseudotachylyte-bearing fault rocks is of particular significance as it offers the possibility of directly sampling the products of dynamic ruptures produced during coseismic faulting at near-focal depths along exhumed fault zones (Sibson 1975). The recent dating at c. 34 Ma of the …
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Publication information: Article title: Eocene Initiation of Ross Sea Dextral Faulting and Implications for East Antarctic Neotectonics. Contributors: Rossetti, Federico - Author, Storti, Fabrizio - Author, Busetti, Martina - Author, Lisker, Frank - Author, et al. - Author. Journal title: Journal of the Geological Society. Volume: 163. Publication date: January 2006. Page number: 119+. © Geological Society Publishing House Jan 2009. Provided by ProQuest LLC. All Rights Reserved.