Geochemical signatures of tephras from Quaternary Antarctic Peninsula volcanoes

Abstract

ABSTRACT. In the northern Antarctic Peninsula area, at least 12 Late Pleistocene-Holocene volcanic centers could be potential sources of tephra layers in the region. We present unique geochemical fingerprints for ten of these volcanoes using major, trace, rare earth element, and isotope data from 95 samples of tephra and other eruption products. The volcanoes have predominantly basaltic and basaltic andesitic compositions. The Nb/Y ratio proves useful to distinguish between volcanic centers located on the eastern (Larsen Rift) and those situated on the western side (Bransfield Rift) of the Antarctic Peninsula. In addition, the Sr/Nb ratio (for samples with SiO 2 <63 wt%), along with Sr/Y, Ba/La, Zr/Hf and Th/Nb are suitable to unequivocally characterize material erupted from every studied volcanic center. Microprobe analyses on volcanic glass show that the samples are generally very poor in K 2 O, and that glass from Bransfield Rift volcanoes is enriched in SiO 2 , while that of Larsen Rift volcanoes tends towards elevated alkali contents. We propose an algorithm for the identification of the source volcano of a given tephra layer using the new geochemical fingerprints. This will contribute to the development of a regional tephrochronological framework needed for future correlations of tephra in climate archives (e.g., marine, lacustrine and ice cores). Keywords: Late Pleistocene, Holocene, Explosive volcanism, Tephra, Source volcano identification, Geochemical fingerprint, Antarctic Peninsula, Bransfield Rift, Larsen Rift. RESUMEN. Geoquímica de tefras de volcanes Cuaternarios de la Península Antártica. En la parte norte de la Península Antártica existen, por lo menos, 12 centros volcánicos del Pleistoceno Tardío-Holoceno que podrían representar las fuentes de horizontes de tefra reconocidos en la región. Se reportan aquí análisis químicos de 10 de estos volcanes, que incluyen análisis de elementos mayores, trazas, tierras raras y composición isotópica de 95 muestras de tefra u otros productos eruptivos. Los volcanes tienen, en su mayoría, composición basáltica a basáltico-andesítica. Las razones Nb/Y resultan útiles para distinguir entre centros volcánicos ubicados al lado oriental (Larsen Rift) de aquellos ubicados al lado occidental (Bransfield Rift) de la Península Antártica. Adicionalmente, las razones Sr/Nb (para muestras con SiO 2 <63 wt%), Sr/Y, Ba/La, Zr/Hf y Th/Nb sirven para caracterizar los productos generados por cada centro volcánico. Análisis de microsonda en vidrio muestran que las rocas estudiadas tienen bajos contenidos de K 2 O, y que vidrios de rocas provenientes de volcanes ubicados en el rift de Bransfield son ricos en SiO 2 , mientras que las de volcanes del rift de Larsen tienden hacía contenidos elevados de álcalis. Se propone un algoritmo para la identificación del volcán de origen de un horizonte de tefra cualquiera, basado en las distintivas composiciones geoquímicas aquí reportadas. Este estudio contribuirá al desarrollo de un marco tefrocronológico regional indispensable para ...

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