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The metamorphic history of the Isua Greenstone Belt, West Greenland

By
Hugh Rollinson
Hugh Rollinson
GEMRU, University of Gloucestershire, Francis Close Hall Campus, Swindon Road, Cheltenham GL50 4AZ, UKDepartment of Earth Sciences, Sultan Qaboos University, Oman
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Published:
January 01, 2002

Abstract

New geological investigations in the c. 3.7–3.8 Ga Isua Greenstone Belt in West Greenland have revealed that the belt comprises a number of separate structural domains. Five such domains have been identified on the basis of lithological and structural differences. This study uses the morphology and compositional zoning of garnet porphyroblasts in pelites to investigate the extent to which the various domains within the greenstone belt preserve contrasting deformational and metamorphic histories. Up to three episodes of garnet growth have been identified in a single domain and significant differences in garnet growth history are noted between domains. A distinction is drawn between the relatively simple metamorphic history of a low-strain zone in the NE of the greenstone belt and other domains where more complex histories are preserved. Combining this result with existing geochronology suggests that in the south and west, the greenstone belt was metamorphosed twice, at c. 3.74 Ga and at c. 2.8 Ga, whereas in the NE there was a single event at 3.69 Ga. Preliminary garnet-rim thermometry indicates that some rocks experienced an early metamorphism in which temperatures exceeded 610°C. Kyanite is thought to have been in equilibrium with these assemblages, indicating pressures of at least 6 kbar. A later prograde metamorphic event shows a temperature rise from 480 to 550°C. The high pressures indicate a crustal thickness of at least 20 km at 3.7 Ga.

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Contents

Geological Society, London, Special Publications

The Early Earth: Physical, Chemical and Biological Development

C. M. R. Fowler
C. M. R. Fowler
University of London, UK
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C. J. Ebinger
C. J. Ebinger
University of London, UK
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C. J. Hawkesworth
C. J. Hawkesworth
University of Bristol, UK
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Geological Society of London
Volume
199
ISBN electronic:
9781862394476
Publication date:
January 01, 2002

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