Antarctic Science

Table of Contents - 1994 - Volume 6, Issue 03  


Papers—Earth Sciences and Glaciology

A probable Early Triassic age for the Miers Bluff Formation, Livingston Island, South Shetland Islands

R. C. R. Willan a1, R. J. Pankhurst a2 and F. Hervé a3
a1 British Antarctic Survey, Natural Environment Research Council, High Cross, Madingley Road, Cambridge CB3 0ET, UK
a2 British Antarctic Survey, c/o NERC Isotope Geosciences Laboratory, Kingsley Dunham Centre, Keyworth, Nottingham NG12 5GG, UK
a3 Departamento de Geología, Universidad de Chile, Casilla 13518, Correo 21, Santiago, Chile.

Article author query
willan r   [PubMed][Google Scholar] 
pankhurst r   [PubMed][Google Scholar] 
hervé f   [PubMed][Google Scholar] 

Abstract

Fifteen samples of very low-grade mudstones from two widely separated sections in the Miers Bluff Formation on Hurd Peninsula yield an Rb-Sr errorchron (MSWD=8.9) corresponding to an age of 243 ± 8 Ma. This age is interpreted as representing effective homogenization, on a kilometres scale, during turbidite deposition and diagenesis in early Triassic times. The initial 87Sr/86Sr ratio 0.7085 ± 0.0003 represents a mature crustal source and is consistent with the re-working of material comparable to that eroded from the Chilean fore-arc accretionary complex. Four further samples, collected near to a zone of quartz-carbonate veins, lie to the right of the errorchron, with two samples having unusually low Sr contents. These samples fall on a 113 Ma reference line and indicate metasomatic disturbance in Cretaceous times. Metasomatism was probably related to hydrothermal alteration accompanying widespread silicification and quartz veining on western Hurd Peninsula. A mid-to late Cretaceous age for metasomatic disturbance agrees with field relations which indicate that the hydrothermal activity preceded or was coeval with the mid- to late Cretaceous period of volcanism on Livingston Island. Hence the hydrothermal rocks are not related to the Eocene Barnard Point pluton, as previously suggested.

(Received December 21 1993)
(Accepted June 3 1994)


Key Words: accretionary complex; rubidium-strontium dating; hydrothermal alteration.

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