Early archaean granulite-facies metamorphism south of Ameralik, West Greenland

W. L. Griffin*, V. R. McGregor, A. Nutman, P. N. Taylor, D. Bridgwater

*Corresponding author for this work

Research output: Contribution to journalArticle

112 Citations (Scopus)

Abstract

Relict high-pressure granulite-facies rocks have been found in the Amîtsoq gneisses and inclusions of the older Akilia supracrustal association, on islands south of Godthåb. Only amphibolite-facies assemblages have been found in Ameralik dykes and younger rocks from this area. The Amîtsoq gneisses are depleted in Rb and U relative to those of Ameralik and Isua. Well-fitted Pb/Pb and Rb-Sr isochrons on Amîtsoq granulites indicate that this depletion, correlated with the granulite-facies metamorphism, occurred ca. 3600 Ma ago. Textural features suggest that the present cpx + opc + gnt + plag + qtz + hbl assemblages evolved from earlierintermediate-P assemblages (cpx + opx + plag), probably during cooling from the metamorphic peak. Re-equilibrium of olderintermediate-P assemblages in local environments of low f{hook}H2O, during the ca. 2800-Ma metamorphism of the Malene supracrustals, is feasible but is considered unlikely. Either interpretation requires crustal thickness of at least 20 km and geothermal gradients of≤30°C/km, ca.3600Ma ago. The higher heat production of early Archaean times was apparently dissipated through oceanic, rather than continental, areas.

Original languageEnglish
Pages (from-to)59-74
Number of pages16
JournalEarth and Planetary Science Letters
Volume50
Issue number1
DOIs
Publication statusPublished - 1980
Externally publishedYes

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