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East Antarctica) TECTONICS, VOL. 27, TC4015, doi:10.1029/2007TC002197, 2008 Click Here for Full Article Recent extension driven by mantle upwelling beneath the Admiralty Mountains (East Antarctica) Claudio Faccenna,1 Federico Rossetti,1 Thorsten W. Becker,2 Stefania Danesi,3 and Andrea Morelli3 Received 10 August 2007; revised 4 April 2008; accepted 17 June 2008; published 27 August 2008. [1] Northern Victoria Land is located at the boundary structed by subsidence and uplift history, is commonly between an extended, presumably hot, region (West considered polyphased, involving an early Cretaceous phase Antarctic Rift System) and the thick, possibly cold, linked to the Gondwana breakup followed by a major East Antarctic craton. The style and timing of Tertiary Cenozoic one [e.g., Cooper et al., 1997; Behrendt et al., deformation along with relationships with the 1991; Tessensohn and Wo¨rner, 1991; Lawver and Gahagan, magmatic activity are still unclear, and contrasting 1994; Davey and Brancolini, 1995; Salvini et al., 1997; Behrendt, 1999; Cande et al., 2000; Mukasa and Dalziel, models have been proposed. We performed structural 2000; Cande and Stock, 2004]. and morphotectonic analyses at the NE termination of [3] There are two outstanding questions concerning the northern Victoria Land in the Admiralty Mountains kinematic and tectonic evolution of the Cenozoic tectonic area, where the relationship between topography, episode in the WARS. First, the pattern of deformation tectonics, and magmatism is expected to be well changes abruptly moving from Victoria Land to the western pronounced. We found evidence of two subsequent Ross Sea shoulder (Figure 1a). Offshore, Oligocene-Miocene episodes of faulting, occurring concurrently with the extension produced localized subsidence along N-S trend- Neogene McMurdo volcanism. The first episode is ing basins [e.g., Davey and De Santis, 2005; Davey et al., associated with dextral transtension, and it is 2006] and oceanic spreading in the Adare Basin [Cande et overprinted by extensional tectonics during the al., 2000; Cande and Stock, 2004]. Onshore, the Ross Sea emplacement of large shield alkaline volcanoes. margin is crosscut by a set of right-lateral NW-SE strike-slip faults that, active from the Eocene onward [Rossetti et al., Upper mantle seismic tomography shows that the 2006], reactivated the Paleozoic (Ross-aged) orogenic fabric extensional regime is limited to regions overlying a [Wilson, 1995; Salvini et al., 1997; Hamilton et al., 2001; low-velocity anomaly. We interpret this anomaly to be Rossetti et al., 2003; Storti et al., 2001, 2007] (Figure 1a). of thermal origin, and have tested the role of large- Second, these tectonic processes are accompanied or scale upwelling on lithosphere deformation in the area. followed by large-scale uplift of an asymmetrically tilted The results of this integrated analysis suggest that the block, the Transantarctic Mountains (TAM) (see inset in morphotectonic setting of the region and the Figure 1a). This mountain belt underwent uplift and magmatism is likely the result of upwelling flow at denudation episodes in the late Cretaceous and in the the boundary between the cold cratonic and the hot Eocene [Fitzgerald and Gleadow, 1988; Fitzgerald, stretched province (WARS), at work until recent time 1992; Balestrieri et al., 1994; Lisker, 2002; Lisker et al., in this portion of the northern Victoria Land. 2006]. Uplift has been related to various kind of crustal flexure [Stern and ten Brink, 1989; van der Beek et al., 1994; Citation: Faccenna, C., F. Rossetti, T. W. Becker, S. Danesi, ten Brink et al., 1997; Busetti et al., 1999], enhanced by and A. Morelli (2008), Recent extension driven by mantle isostasy related to differential erosion [Stern et al., 2005], upwelling beneath the Admiralty Mountains (East Antarctica), locally localized along strike-slip fault systems [Salvini et al., Tectonics, 27, TC4015, doi:10.1029/2007TC002197. 1997; Stackebrandt, 2003; Rossetti et al., 2006], or related to a thermal anomaly [e.g., ten Brink and Stern, 1992; ten Brink 1. Introduction et al., 1997; Behrendt, 1999]. Alkaline Cenozoic volcanism indeed accompanied formation of the WARS [e.g., Wo¨rner, [2] The Ross Sea region (namely Victoria Land and Ross 1999, and references therein]. Magmatism started at about Sea) is located within the Western Antarctic Rift System 48 Ma in north Victoria Land [Tonarini et al., 1997; Rocchi et (WARS), one of the largest extended and stretched conti- al., 2002], getting particularly abundant over the last 15 Ma nental rifts worldwide [e.g., Wo¨rner, 1999, and references (McMurdo Volcanic Province [LeMasurier, 1990]), with a therein]. The evolution of the rifting, as mainly recon- MORB- to OIB-type (HIMU source) imprinting [Rocholl et al., 1995, Rocchi et al., 2002] (Figure 1a). 1Dipartimento Scienze Geologiche, Universita` Roma Tre, Rome, Italy. [4] The purpose of this paper is to unravel the relation- 2University of Southern California, Los Angeles, California, USA. ships between tectonics and magmatism in order to shed 3Istituto Nazionale di Geofisica e Vulcanologia, Bologna, Italy. light into the recent dynamic evolution of this region. To achieve this purpose, we performed a geological-structural Copyright 2008 by the American Geophysical Union. survey over the Admiralty Mountains region, positioned on 0278-7407/08/2007TC002197$12.00 TC4015 1of13 TC4015 FACCENNA ET AL.: MANTLE UPWELLING AT ADMIRALTY MOUNTAINS TC4015 Figure 1. (a) Tectonic map of the Ross Sea region with main structural features and distribution of McMurdo volcanics (modified after Salvini et al. [1997], Cande et al. [2000], Davey and De Sanctis [2005], and Davey et al. [2006]). The inset shows the Antarctic continent and the West Antarctic Rift system (WARS). Location of the study area is shown. MBL, Marie Bird Land; NVL, north Victoria Land. (b) Cross-section AA0 shows the main structural archtecture across NVL and their relationships with topography and magmatism along with (c) the corresponding upper mantle DM01 model [Danesi and Morelli, 2001] tomographic section (see Figure 2). the western shoulder of the Adare Basin, where uplift [Van mantle density anomalies. This integrated analysis shows der Wateren et al., 1999; Baroni et al., 2005], volcanism that: (1) tectonic activity persisted in the region until recent and tectonics [Mu¨ller et al., 2005; La¨ufer et al., 2006; Storti time, exerting control on the Pliocene-Pleistocene McMurdo et al., 2007] are expected to be particularly pronounced volcanism with a continuous evolution from strike-slip to (Figure 1a and Figure 3 in section 4). We integrate our extensional faulting, probably during latest stage of TAM surface crustal data with the upper mantle tomographic uplift; (2) the area of deformation is localized at the analysis of Danesi and Morelli [2001] in order to investi- transition zone between the cold East Antarctic craton and gate the possibly deep origin of the tectonic signal. We test the stretched hot continental crust of the WARS; and (3) an the result of our model by comparing the shear stress active mantle upwelling model is considered as the most reconstructed by means of field survey with the one likely explanation for the tectonic evolution of this portion expected from a large-scale mantle flow model driven by of the WARS. This model reconciles the recent tectonic 2of13 TC4015 FACCENNA ET AL.: MANTLE UPWELLING AT ADMIRALTY MOUNTAINS TC4015 faulting, geomorphic evidence, volcanism, and the deep oceanic spreading from about 43 to 26 Ma [Cande et al., seismological structure. 2000; Cande and Stock, 2004]. The uplift and erosional history of the Admiralty Mountains is considered to be mainly Cenozoic [Lisker, 2002; Fitzgerald and Gleadow, 2. Geological Background and the Admiralty 1988]. Preliminary fission track analysis near Mt. Minto Mountains Region attests for the presence of an Eocene (48 Ma) denudation event [Redfield, 1994]. Morphological analysis in the area [5] The Transantarctic Mountains separate the thinned continental lithosphere of the WARS from the East Antarc- shows the development of a vigorous fluvial erosion event tic craton (Figure 1). In the Northern Victoria Land, the controlled and adapted to the main tectonic network until at geomorphological scenario of the TAM abruptly changes least Eocene-Oligocene boundary [Baroni et al.,2005]. along strike crossing the Lanterman Fault, a major structural Finally, the presence of subacqueous volcanism, now stand- boundary separating the Neoproterozoic-Early Paleozoic ing at almost 400 m, shows a substantial post-eruptive (Late Wilson Terrane from the Admiralty Block (the Bowers- Miocene–Pliocene) uplift [Mortimer et al., 2007]. Robertson Bay terranes assembly [Tessensohn, 1994]). South of the Lanterman Fault, the exhumed roots of the 3. Mantle Structure Early Paleozoic Ross Orogen are peneplanned below the Gondwanian terrestrial sequence, Permo-Traissic to Jurassic [8] The structure of the upper mantle beneath Antarctica in age [Lisker et al., 2006, and references therein]. North of has been imaged through regional tomographic techniques the Lanterman Fault, the Admiralty Block landscape is [Danesi and Morelli, 2001; Ritzwoller et al., 2001; Sieminski characterized by an Alpine-type morphology shaped by et al., 2003] and local investigations, mostly from temporary narrow valleys and sharp cliffs with peaks reaching altitudes deployments [Bannister et al., 2000, 2003; Lawrence et al., of more than 4000 m in the Admiralty Mountains area
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