14 research outputs found
Volcano-ice-sea interaction in the Cerro Santa Marta area, northwest James Ross Island, Antarctic Peninsula
We present here the results of detailed mapping, lithofacies analysis and stratigraphy of the Neogene James Ross Island Volcanic Group (Antarctic Peninsula) in the Cerro Santa Marta area (northwest of James Ross Island), in order to give constraints on the evolution of a glaciated volcanic island. Our field results included recognition and interpretation of seventeen volcanic and glacial lithofacies, together with their vertical and lateral arrangements,supported by four new unspiked K?Ar ages. This allowed us to conclude that the construction of the volcanic pile in this area took place during two main eruptive stages (Eruptive Stages 1 and 2), separated from the Cretaceous bedrock and from each other by two major glacial unconformities (U1 and U2). The U1 unconformity is related to Antarctic Peninsula Ice sheet expansion during the late Miocene (before 6.2 Ma) and deposition of glacial lithofacies in a glaciomarine setting. Following this glacial advance, Eruptive Stage 1 (6.2?4.6 Ma) volcanism started with subaerial extrusion of lava flows from an unrecognized vent north of the study area,with eruptionslater fed from vent/s centered at Cerro Santa Marta volcano, where cinder cone deposits and a volcanic conduit/lava lake are preserved. These lava flows fed an extensive (N7 km long) hyaloclastite delta system that was probably emplaced in a shallow marine environment. A second unconformity (U2)was related to expansion of a local ice cap, centered on James Ross Island, which truncated all the eruptive units of Eruptive Stage 1. Concomitant with glacier advance, renewed volcanic activity (Eruptive Stage 2) started after 4.6 Ma and volcanic products were fed again by Cerro Santa Marta vents. We infer that glacio volcanic eruptions occurred under a moderately thin (~300 m) glacier, in good agreement with previous estimates of paleo-ice thickness for the James Ross Island area during the Pliocene.Fil: Calabozo, Fernando Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Strelin, Jorge Adrián. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Orihashi, Yuji. The University Of Tokyo; JapónFil: Sumino, Hirochika. The University Of Tokyo; JapónFil: Keller, Randall A.. State University of Oregon; Estados Unido
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Geochemistry of back arc basin volcanism in Bransfield Strait, Antarctica: Subducted contributions and along-axis variations
Bransfield Strait is a Quaternary, ensialic back arc basin at the transition from rifting
to spreading. Fresh volcanic rocks occur on numerous submarine features distributed
along the rift axis, including a discontinuous neovolcanic ridge similar to the nascent
spreading centers seen in some other back arc basins. Smaller edifices near the northeast
end of the rift yielded basalts with the most arc-like compositions (e.g., high large-ion
lithophile element/high field strength element and ⁸⁷Sr/⁸⁶Sr). The most mid-ocean ridge
basalt (MORB)-like basalts are from a large, caldera-topped seamount and a 30-km-long
axial neovolcanic ridge toward the southwest end of the rift, but these two features also
yielded andesite and rhyolite, respectively. The volcanic and geochemical variations are
not systematic along axis and do not reflect the unidirectional propagation of rifting
suggested by geophysical data. The most depleted basalts have major and trace element
characteristics indistinguishable from MORB except for slightly higher Cs and Pb
concentrations. Pb isotopic ratios show little variation compared to Sr and Nd isotopic
ratios and do not extend to the depleted Pb isotopic ratios found in other back arc basins.
Either the depleted mantle beneath Bransfield Strait has higher than normal Pb isotopic
ratios or the subducted component beneath Bransfield Strait has such high Pb
concentrations that it dominates the Pb isotopic composition of the Bransfield Strait
mantle without significantly affecting the Sr and Nd isotopic compositions. Metalliferous
sediments and fluids extracted from a subducting slab may have the necessary high
concentrations of Pb.Keywords: volcanism, Bransfield Strait, geochemistry, back arc basin, Antarctica, recyclingKeywords: volcanism, Bransfield Strait, geochemistry, back arc basin, Antarctica, recyclin