Mt. Takahe is a large, late Quaternary trachyte shield volcano that rises through 2000 + m of the West Antarctic ice sheet. It is composed mostly of ne-trachyte, hy-ol-trachyte, and qz-trachyte flows, with subordinate basanite, intermediate rocks, and pantellerites. All rock types can be adequately modeled by fractional crystallization of basanite - the only basaltic rock exposed here. The ne-trachytes can be explained by a single stage of low-pressure fractionation near the base of the upper crust. Models of oversaturated rocks require a period of evolution at a depth of ~ 35 km, below the stability field of plagioclase, where fractionation of kaersutite and associated high pressure minerals will yield silica oversaturated residual magmas. This is then followed by a period of fractionation at a depth of ~ 3 km, where peralkalinity and Fe-enrichment are acquired. Pantellerite compositions span virtually the entire spectrum of peralkalinity, Fe-enrichment, LILE–enrichment, and SiO2 values, and seem to represent a range of residence times in upper crustal vs., upper mantle magma chambers. Mt. Takahe is unusual among Marie Byrd Land volcanoes for its geochemical anomalies. These include the lowest 143Nd/144Nd ratios in West Antarctica, and unusually high but unpredictable Ba values. These anomalies are believed to originate in a pre-85 Ma subduction mélange at the base of the lithosphere, which seems to be the source of Mt. Takahe basaltic rocks.
Bibliographical noteFunding Information:
Field and laboratory work on the geochemistry and petrology of Mt. Takahe volcano has been supported by NSF grants DPP 80-20836 and # 0536526 (to WEL), administered by the Office of Polar Programs. WEL thanks the Institute of Arctic and Alpine Research (INSTAAR) for funds to cover publication costs. We are grateful to Gary Ernst for a critical and helpful review of an early draft of the manuscript. WEL gratefully acknowledges a lot of help from Stan Hart, over many years, which has always led to an improved understanding and interpretation of trace element and isotope data. Stimulating and constructive reviews by Phil Leat and John White greatly improved the paper and are gratefully acknowledged. WEL thanks Nick Banks, Nelia Dunbar, Pam Ellerman, Mark Losleben and Bill McIntosh for congenial partnership in the field.
- Residence times