Seismic imaging of the upper mantle under the Erebus hotspot in Antarctica
Introduction
The Antarctic continent is tectonically divided into the stable East Antarctic (EA) craton and West Antarctic Rift System (WARS) by the Transantarctic Mountains (TAM). The EA craton is a stable Precambrian shield and was a segment of the core of the Gondwanland supercontinent that was assembled during the Neoproterozoic. The EA craton under the polar ice sheet is inferred to include pan-African age belts, Grenville age provinces, Proterozoic domains, and Archean cratons (Yoshida and Santosh, 1995, Fitzsimons, 2000, Fitzsimons, 2003, Santosh et al., 2009, Maruyama et al., 2007, Rino et al., 2008, Veevers and Saeed, 2008, Veevers et al., 2008). The WARS, one of the major active continental rifts on the Earth, consists of several young geological and tectonic units that are rather mobile on a geological time scale (e.g., Roult and Rouland, 1994, Santosh et al., 2001, Fitzgerald, 2002, Elliot and Fanning, 2008, Federico et al., 2009, Vaughan and Pankhurst, 2008). Several hotspots are located in and around the Antarctica and they have played an important role in the tectonic history of the Gondwana breakup (e.g., Windley, 1995). Ross Island in the Ross Sea, West Antarctica (Fig. 1) is entirely volcanic in origin. It hosts four principal volcanoes—Mount Bird, Mount Terror, Terra Nova and Mount Erebus, as well as numerous smaller volcanoes and lava flow. While the first three ones are extinct major volcanic centers, Mount Erebus is an active volcano. As the world's southernmost active volcano and one of the loftiest volcanoes (elevation 3795 m) of the world, the Mount Erebus is the largest volcano by volume (nearly 1035 km2) in the Antarctica continent, and it is less than one million years old. The most recent eruption of the Mount Erebus began in 1972. It has one of the Earth's few long-lived convecting lava lake within a summit crater. The composition of lava within the lava lake of the Mount Erebus volcano is alkali, specifically called anorthclase phonolite, which is common in rift volcanoes (LeMasurier and Thomson, 1990, Kyle et al., 1992, Simkin and Siebert, 1994, de Wit and Anderson, 2003).
Many seismological studies by different researchers were carried out to study the crust and upper mantle structure under the Antarctic region. In the EA craton the crustal thickness varies from 35 to 45 km, while in the Ross Island region the crustal thickness varies from 18 to 25 km (Behrendt, 1999, Bannister et al., 2003, Lawrence et al., 2006b, Watson et al., 2006). The transition zone thickness (266 ± 10 km) under the WARS is slightly larger than the global average (Reusch et al., 2008).
By using data recorded by the sparse seismic network in or around Antarctic or global seismic stations, previous tomographic images show low-velocity (low-V) anomalies at the upper mantle depths beneath the WARS (e.g., Roult et al., 1994, Danesi and Morelli, 2001, Ritzwoller et al., 2001, Zhao, 2001, Zhao, 2007, Zhao, 2009, Kobayashi and Zhao, 2004, Sieminski et al., 2003, Morelli and Danesi, 2004). The low-V anomaly in the upper mantle beneath the WARS was also observed in the recent seismic studies by using a dense local seismic network (Lawrence et al., 2006a, Lawrence et al., 2006b, Watson et al., 2006). The observed low-V anomaly is interpreted as a thermal anomaly either due to the presence of a mantle plume (Behrendt, 1999, Zhao, 2007, Zhao, 2009, Kobayashi and Zhao, 2004, Sieminski et al., 2003, Morelli and Danesi, 2004, Watson et al., 2006) or due to small-scale convection under the WARS (Ritzwoller et al., 2001, Roult et al., 1994).
These earlier seismological studies focused mainly on the problem of the uplift of the TAM and the evolution of the WARS. However, it is still debatable whether the Mount Erebus, the world's southernmost active volcano, is a hotspot or not (e.g., Sleep, 1990, Duncan and Richards, 1991, Zhao, 2007). In this study we focus on understanding the deep structure and evolution of the Mount Erebus through a detailed 3-D P-wave velocity imaging by applying a tomographic method to teleseismic travel times recorded by 42 portable seismic stations in and around the Mount Erebus.
Section snippets
Data and method
We used data from 41 temporary broadband seismic stations of the Trans Antarctic Mountains Experiment (TAMSEIS) and one seismic station of the Mount Erebus Volcano Observatory Seismic Network (ER) (Fig. 1) (Lawrence et al., 2006a, Lawrence et al., 2006b). During November 2001 to December 2003, the TAMSEIS was conducted along three profiles: (1) A 1300-km linear array with 17 seismic stations extending from the central regions of the EA to TAM (array 1), (2) an intersecting 400-km denser array
Analysis and results
We conducted several tomographic inversions using different grids, and preferred a grid spacing of 0.5° and 1.0° in latitude and longitude directions, respectively (Fig. 5). The vertical grid spacing ranges from 40 to 200 km increasing with depth. Inversions were also performed by using various damping and smoothing parameters. The pattern of the tomographic images is generally stable, although there are slight changes in the amplitude of the velocity anomalies.
Fig. 8, Fig. 9 show our optimal
Discussion
The seismic velocity variations revealed by seismic tomography may reflect changes in composition and/or temperature. Large P-velocity reduction (up to 2%) in the upper mantle due to compositional variations is unlikely (Karato, 1993, Sobolev et al., 1997, Faul and Jackson, 2005). However, accounting for first-order effects like anharmonicity (Anderson et al., 1992, Duffy and Anderson, 1989) and anelasticity (Karato, 1993, Sobolev et al., 1997), the amplitude of the low-V anomaly (up to 2%)
Conclusions
We determined a detailed 3-D P-wave velocity structure of the upper mantle beneath the Mount Erebus volcano using a large number of high-quality arrival-time data collected from original seismograms of teleseismic events recorded by portable seismic networks. Our resulting model shows high-velocity (high-V) anomalies beneath the EA craton. Beneath the Mount Erebus volcanic region a significant low-V anomaly of nearly circular symmetry (about 250–300 km in diameter) exists down to about 200 km
Acknowledgments
We thank the IRIS Data Management Center for providing the waveform data used in this study. We are indebted to Dr. Guoming Jiang for his assistance during the analysis and useful discussions. S. Gupta thanks the NGRI director for his encouragement and support and the Department of Science and Technology, Government of India for the BOYSCAST fellowship to study at Tohoku University, Japan. This work was partially supported by a grant (Kiban-A 17204037) from the Japan Society for the Promotion
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2021, Geochimica et Cosmochimica ActaCitation Excerpt :Volcanism is associated with Cenozoic intraplate rifting within the West Antarctic Rift System (Behrendt, 1999; Jordan et al., 2020). Ross Island volcanism has been explained by a mantle plume beneath Erebus (Kyle et al., 1992; Phillips et al., 2018) but is still subject to speculation (e.g., Storey et al., 1999; Rocchi et al., 2002, 2005; Gupta et al., 2009; Panter, 2021). Each volcanic center on Ross Island has a slightly different magmatic evolutionary path, with the EL exhibiting a hotter, drier, magmatic plumbing system than the kaersutite-bearing DVDP lineage rocks found at the 3 volcanic centers (Bird, Terror and Hut Point) (Fig. 1) that radially surround Erebus (Kyle et al., 1992; Iacovino et al., 2016; Rasmussen et al., 2017).
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2019, Chemical GeologyCitation Excerpt :A popular model has involved the presence of an active mantle plume beneath the WARS, since the Early Cretaceous. Evidence in favour of this model includes the similarity in composition of WARS lavas and some ocean island basalts (OIB), an uplifted dome in the Marie Byrd Land suggesting dynamic topography, the high heat flow in the Ross Sea, low P-wave velocities beneath Ross Island, and the modest extension that is accompanied by large-volume Cenozoic magmatism in the WARS (LeMasurier and Rex, 1989; Behrendt et al., 1991; Hole and LaMasurier, 1994; LeMasurier and Landis, 1996; Storey et al., 1999; Gupta et al., 2009; Hansen et al., 2014). Alternatively, rift-related melting of an enriched mantle source, either as a ‘fossil’ plume head formed during mid-Cretaceous break-up of New Zealand from Antarctica (Rocholl et al., 1995; Panter et al., 2000; Finn et al., 2005), or melting of amphibole- or phlogopite-rich veins formed by plume- and/or subduction-related metasomatism between 500 and 100 Ma, have also been proposed (Panter et al., 2006; Nardini et al., 2009).
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2019, Physics of the Earth and Planetary InteriorsCitation Excerpt :Erebus is an intraplate stratovolcano (~3794 m high) of phonolitic composition that is located at the southern end of Terror Rift within the West Antarctica Rift system (Kyle et al., 1992; Behrendt, 1999) (Fig. 1). Volcanism there is a consequence of crustal rifting on top of a mantle plume, as evidenced by tomographic images that show a low velocity anomaly extending down to 400 km within the mantle (Gupta et al., 2009). The volcanic edifice of Erebus exhibits a summit plateau that hosts the main crater with a diameter of 600 m.