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FIGURE 1 The Cretaceous West Antarctic rift system at ca. 90 Ma, illustrating the positions of Marie Byrd Land and New Zealand/Campbell Plateau along the East Gondwana margin. The rifted margin corresponds to the −1500 m contours (dashed-line pattern). The tight fit of the reconstruction, the linear to curvilinear continental margin, and the pronounced depth increase suggest fault control and steep fault geometry. The diagram is based on the reconstructions of Lawver and Gahagan (1994) and Sutherland (1999). The present-day position of the Transantarctic Mountains, as labeled, corresponds to the western tectonic boundary of the West Antarctic Rift System. FM = Fosdick Mountains; EP = Edward VII Peninsula; 270 = DSDP site 270.

The lesser-known phase of extension and lithospheric thinning that brought about formation of the vast rift system (~1.2 × 106 km2) did not occur in Cenozoic but in Mesozoic time (Tessensohn and Wörner, 1991; Lawver and Gahagan, 1994; Luyendyk, 1995). Although the origins of the WARS may be linked to Weddell Sea opening and Ferrar magmatism in the Jurassic (Grunow et al., 1991; Wilson, 1993; Jokat et al., 2003; Elliot and Fleming, 2004), dramatic intracontinental extension occurred in Cretaceous time. Much of the basis of knowledge about the Ross Sea sector of the rift comes from ocean bottom seismograph, multichannel seismic reflection, and gravity surveys that revealed a N-S structure of elongate basins marked by a positive gravity anomaly and high seismic velocities in the lower crust and 1-4 km of inferred Mesozoic sedimentary fill (Cooper and Davey, 1985; Cooper et al., 1997; Trey et al., 1997). Paradoxically, major sedimentary infilling of basins with material postdating regional unconformity RU6 evidently was delayed until the Eocene to Miocene (Hamilton et al., 1998; Wilson et al., 1998; Cape Roberts Science Team, 2000; Luyendyk et al., 2001; Karner et al., 2005). This is despite the rapidity of the large magnitude extension, on the order of 600 km in the south, up to >1000 km in the north achieved in as little as 20 m.y. (DiVenere et al., 1996; Luyendyk et al., 1996). A second paradox is that breakup between WANT and New Zealand (NZ) did not exploit rift structures but rather cut at a high angle across basement highs and basins of the Ross Sea (Tessensohn and Wörner, 1991; Lawver and Gahagan, 1994; Sutherland, 1999). Wrench deformation and the presence of strike slip transfer systems was postulated (Grindley and Davey, 1982) but not substantiated from exposures on land.

New perspective on intracontinental extension in the WARS comes from geological and geophysical research that investigates the exposed bedrock of WANT, NZ, and the Tasman Sea region (Figure 1). WANT, NZ, and submarine plateaus formed a contiguous segment of the convergent margin of East Gondwana in Early Cretaceous time, with arc magmatism recorded in Marie Byrd Land-NZ. Transtension–extension occurred in a back arc to inboard setting, forming the intracontinental West Antarctic rift system and Great South Basin-Campbell Plateau extensional province (Figure 1).

Since 1990, data acquired from geological investigations on land and from airborne and marine geophysical surveys in the region of Marie Byrd Land have dramatically increased the understanding of the eastern WARS, with consequences for our conception of the Cretaceous to Present multistage evolution of the West Antarctic rift system as a whole. The aim of this paper is to summarize the tectonic evolution of western Marie Byrd Land (MBL) (Figure 2) and of neighboring segments of the proto-Pacific margin of East Gondwana (Figure 3). Little affected by Cenozoic events (cf. Fitzgerald, 2002; Stock and Cande, 2002), the eastern Ross Sea region preserves a clear record of the kinematics, magmatism, and thermal history of the Early Cretaceous large-scale opening of the WARS.

Knowledge of the Cretaceous tectonic evolution of the WARS-NZ-Tasman Sea region provides an important foundation for contemporary research in WANT, including studies of the Cretaceous to present landscape evolution (LeMasurier and Landis, 1996; LeMasurier, 2008) involving a postulated orogenic plateau (Bialas et al., 2007; Huerta, 2007), the origins of the Southern Ocean’s diffuse alkaline magmatism (Finn et al., 2005; Rocchi et al., 2005), the causes for Cenozoic structural reactivation (e.g., Salvini et al., 1997; Rossetti et al., 2003a,b) and seismicity (Winberry and Anandakrishnan, 2004), and the affects of inherited structures upon ice-bedrock interactions of the dynamic WAIS (Lowe and Anderson, 2002; Holt et al., 2006; Vaughan et al., 2006; Sorlien et al., 2007).



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