Late Sinistral Shearing along Gondwana’s Paleo‐Pacific Margin in the Ross Orogen, Antarctica: New Structure and Age Data from the O’Brien Peak Area

Abstract

New isotopic data from O'Brien Peak, Antarctica, provide constraints on the timing of deformation within the Ross Orogen in the Queen Maud Mountains. U-Pb data, in conjunction with structural data from a mylonitic granite, indicate that sinistral, orogen-parallel ductile shearing occurred after ∼489 Ma, the granite's crystallization age, and , the 40 Ar-39 Ar cooling ages of undeformed and synkinematic white mica, respectively. before 478 ‫ע‬ 3 Ma to 473 ‫ע‬ 3 Ma These data provide evidence for the youngest sinistral shearing event within the Ross Orogen to date and indicate that left-oblique subduction possibly continued into the Early Ordovician along Gondwana's paleo-Pacific margin.

Long‐lived orogenic construction along the paleo‐Pacific margin of Gondwana (Deep Freeze Range, North Victoria Land, Antarctica)

“…Early Ordovician 40 Ar‐ 39 Ar metamorphic ages are also reported from the Lanterman Range area, and framed within a scenario dominated by oblique convergence [ Goodge and Dallmeyer , 1996; Crispini et al , 2007]. Similarly, Early Ordovician ages have been also documented in Queen Maud Mountains of southern Victoria Land and attributed to late sinistral shearing [ Paulsen et al , 2008]. Collectively, our results integrated with the these data indicate that (1) the Early Ordovician corresponded to a period of profound tectonic reorganization all along the Wilson Terrane and (2) partitioned orthogonal and oblique convergence dominate the Early Ordovician tectonic scenario.…”

“…Evidence for polyphase deformation along this margin is provided by the Wilson Terrane of northern Victoria Land (Figure 1c), since it is extensively crosscut by ductile shear zones of variable thickness, kinematics and metamorphic conditions that overprint a complex terrain history (Wilson Mobile Belt in the work by Roland et al [2004]). These shear zone were active during the polyphase metamorphic evolution of the Ross orogenic cycle [e.g., Goodge and Dallmeyer , 1996; Capponi et al , 1999; Musumeci and Pertusati , 2000; Federico et al , 2006], and some of them were active during its late‐stage evolution [ Goodge and Dallmeyer , 1996; Läufer and Rossetti , 2003; Paulsen et al , 2008] or postdate Ross‐aged metamorphism and deformation [ Crispini et al , 2007; Di Vincenzo et al , 2007].…”

“…Key to labels: BT, Bowers Terrane; LF, Lanterman Fault; RBT, Robertson Bay Terrane; WT, Wilson Terrane. Dallmeyer, 1996;Läufer and Rossetti, 2003;Paulsen et al, 2008] or postdate Ross-aged metamorphism and deformation [Crispini et al, 2007;Di Vincenzo et al, 2007].…”

Detrital mineral ages from the Ross Supergroup, Antarctica: Implications for the Queen Maud terrane and outboard sediment provenance on the Gondwana margin

“…,Mellish et al (2002),Myrow et al (2002),Read et al (2002),Vogel et al (2002);Goodge et al (2002),Curtis et al (2004),Goodge et al (2004a,b),Paulsen et al (2004),Stump et al (2004),Wysoczanski and Allibone (2004),Cottle and Cooper (2006a,b),Stump et al (2006Stump et al ( , 2007,Talarico et al (2007),Paulsen et al (2008),Cooper et al (2010),Goodge et al (2012), andPaulsen et al (2013).…”

Correlation and Late-Stage Deformation of Liv Group Volcanics in the Ross-Delamerian Orogen, Antarctica, from New U-Pb Ages

“…More recent zircon U-Pb geochronology indicates that emplacement of intrusive and volcanic rocks primarily occurred after 535 Ma (Encarnación and Grunow 1996;Van Schmus et al 1997;Paulsen et al 2013), and 40 Ar-39 Ar data indicate ∼500-475 Ma metamorphic and igneous cooling ( fig. 3; Encarnación 2000a, 2000b;Paulsen et al 2004Paulsen et al , 2008Paulsen et al , 2013.…”