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Mineralogy and formation of evaporite deposits from the Lewis Cliff ice tongue, Antarctica

Published online by Cambridge University Press:  05 September 2014

Tingting Liu*
Affiliation:
Department of Geological Sciences, Indiana University, 1001E 10th Street, Bloomington, IN 47405, USA
David L. Bish
Affiliation:
Department of Geological Sciences, Indiana University, 1001E 10th Street, Bloomington, IN 47405, USA
Richard A. Socki
Affiliation:
UTAS, Jacobs-JETS, NASA Johnson Space Center, Houston, TX 77058, USA
Ralph P. Harvey
Affiliation:
Department of Earth, Environment, and Planetary Sciences, 112 AW Smith Building, Case Western Reserve University, Cleveland, OH 44106, USA
Eric Tonui
Affiliation:
Upstream Research & Technology, BP America, 501 Westlake Park Boulevard, Houston, TX 77079, USA

Abstract

The mineralogy of evaporites from the Lewis Cliff ice tongue (LCIT), Antarctica, and their mineral stabilities and transformation behaviours under different temperature and relative humidity (RH) conditions have been evaluated to elucidate formation mechanism(s). A variety of sodium (Na)-rich evaporite minerals were documented using RH-controlled powder X-ray diffraction (XRD) methods including Na-sulfates (mirabilite and thenardite), Na-carbonate/bicarbonates (nahcolite, occasional trona and natron) and Na-borates (qilianshanite and borax). Mirabilite begins to dehydrate to thenardite, and natron to trona and natrite when exposed to room temperature, even when maintained at RH values similar to those measured at the LCIT (50–70%). The boron-mineral qilianshanite was discovered for the first time in Antarctica within the evaporite mounds. The mirabilite-rich mounds are deduced to have formed via a freezing/sublimation process that occurred in glacial or subglacial bodies of water supplied by glacial tills containing microbially oxidized sulfate ions. The needle-like nahcolite crystals growing on the exteriors of the mounds suggest a dissolution/precipitation process involving atmospheric CO2 and water. The co-existence of nahcolite and boron-bearing minerals indicates the presence of a Na+-, HCO3 -- and boron-bearing alkaline brine, which produces qilianshanite as a secondary mineral by reaction of nahcolite and borax in atmospheric CO2 and H2O.

Information

Type
Earth Sciences
Copyright
© Antarctic Science Ltd 2014 

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