No plume, no rift magmatism in the West Antarctic Rift

Abstract

The West Antarctic Rift system is one of the largest areas of crustal extension in the world. Current interpretations of its driving mechanisms rely mostly on the occurrence of one or more mantle plumes that was active during the Cenozoic or the Mesozoic. The plume hypotheses are mainly based on the similarity between the basalts from the West Antarctic Rift and those associated with long-lived hotspot tracks. The geochemical signature of the mafic rocks is indeed typical of ocean island basalts (OIB), from a source with a tendency to high , i.e., high U/Pb (HIMU) mantle. However, these features cannot be exclusively interpreted in terms of a plume sampling very old slab material recycled at great depth for a long time (10 9 yr): a metasomatic event at a time on the order of 10 8 yr (i.e., Cretaceous) is sufficient to have produced the required source features.Geometric-chronological relationships between magmatism and local tectonic activity further constrain the scenario. In Victoria Land, the occurrence of plutons, dike swarms, and volcanic edifices since the Middle Eocene indicates that magma emplacement is guided by the dextral strike-slip fault systems that dissect the rift shoulder in this area. The faults were active at their Ross Sea termination in Cenozoic time, coeval with magma emplacement, as demonstrated by the ca. 34 Ma age of a pseudotachylyte generated in the right-lateral fault system exposed in northern Victoria Land. Middle Eocene activity is also inferred for the Pacific termination of the faults from apatite fission track thermochronology. In a wider perspective, these faults are in striking continuity with Southern Ocean fracture zones, and mantle tomography depicts a thermal anomaly of linear (not circular) shape overlapping the belt of the same fracture zones, suggesting that the anomaly is related to lithospheric geometry and movements rather than to deep plumes.The lack of any decisive evidence for plume activity is thus associated with the evidence that large-scale tectonic features drove magma emplacement: the Cenozoic fault systems reactivated Paleozoic tectonic discontinuities, and their activity is dynamically linked to the Southern Ocean fracture zones. As an alternative to both active (plume-driven) rifting and passive rifting, we propose that lithospheric strike-slip deformation could have promoted transtension-related decompression melting of a 435 *

The upper lithostratigraphic unit of ANDRILL AND-2A core (Southern McMurdo Sound, Antarctica): Local Pleistocene volcanic sources, paleoenvironmental implications and subsidence in the southern Victoria Land Basin

“…The cause of the volcanism here and for the rest of the West Antarctic rift is still under discussion (Finn et al, 2005). Plume-driven rifting and volcanism has been proposed (Behrendt et al, 1991;Kyle et al, 1992), and more recently, alternative explanations promote decompression melting of enriched metasomatized continental lithosphere by intraplate stresses (Rocchi et al, 2002(Rocchi et al, , 2003(Rocchi et al, , 2005, and/or by contact with warm Pacific mantle (Finn et al, 2005). In this context, the ANDRILL project also contributes to the knowledge of possible feedback mechanisms between volcanism, tectonism and climate.…”

Tectonics of the West Antarctic rift system: new light on the history and dynamics of distributed intracontinental extension

“…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).…”

“…By far the better-known rift phase is the mid-Cenozoic to Present interval. Widespread basaltic volcanism (Behrendt et al, 1994(Behrendt et al, , 1996Finn et al, 2005;Rocchi et al, 2005), slow mantle seismic velocities (Danesi and Morelli, 2001;Ritzwoller et al, 2001;Sieminski et al, 2003), and anomalous elevation of thinned continental crust (LeMasurier and Landis, 1996;LeMasurier, 2008) are the hallmarks of the Cenozoic rift. The Victoria Land Basin and Terror rift, on the western limit of the WARS, record modest extension on the order of 150 km in Eocene-Oligocene time (Stock and Cande, 2002;Davey and DeSantis, 2006).…”

Origin of the Bermuda volcanoes and the Bermuda Rise: History, observations, models, and puzzles

“…Time correlation diagram, showing selected, more or less coeval tectonic or magmatic events at Bermuda and elsewhere in the world. Assembled from numerous sources, including Bailey and Woolley, 2005;Cande and Stock (2004), Dalrymple and Clague (1976), Kristoffersen and Talwani (1977), Oldow et al (1989), Palmer and Geissman (1999), Rocchi et al (2005), Rona and Richardson (1978), Sharp and Clague (2002), Southworth et al(1993), Tarduno (2005), Winterer et al (1989), and various data relating to Bermuda, as discussed in this paper. …”

“…This was preceded according to the same authors by the start of the main episode of Cenozoic East-West Antarctic separation and the initiation of seafloor spreading in the Adare Basin, and other plate rearrangements at about Chron 20 time (42)(43)(44)(45). 30 Cenozoic uplift and igneous activity in the West Antarctic Rift area (Victoria Land and Ross Sea; Rocchi et al, 2005)) bears striking resemblance to what happened far away in Bermuda: A main denudation-uplift in the Middle Eocene was accompanied by igneous activity dating from 48 to 35 Ma, with a geographic shift in activity ca. 33 Ma.…”