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The emergence of the Eoarchaean proto-arc: evolution of a c. 3700 Ma convergent plate boundary at Isua, southern West Greenland

By
Allen P. Nutman
Allen P. Nutman
1
GeoQuEST Research Centre, School of Earth & Environmental Sciences, University of Wollongong, Wollongong, NSW 2522, Australia
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Vickie C. Bennett
Vickie C. Bennett
2
Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
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Clark R. L. Friend
Clark R. L. Friend
3
Gendale, Tiddington, Oxon, OX9 2LQ, UK
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Published:
January 01, 2015

Abstract

Eoarchaean juvenile crust formed as ‘proto-arcs’. The northern side of the Isua supracrustal belt is an archetypal proto-arc, with ≥3720 Ma boninites, c. 3720 Ma basalts and gabbros, 3720–3710 Ma andesites, diorites and mafic tonalites, 3710–3700 Ma intermediate-felsic volcanic and sedimentary rocks and 3700–3690 Ma chemical sedimentary rocks. On its northern side there is an extensive body of 3700–3690 Ma tonalite. During its evolution, the c. 3700 Ma Isua volcanic–sedimentary assemblage was partitioned into tectonic slices, with intercalation of mantle dunites with pillow basalts, prior to intrusion of c. 3710 Ma quartz diorites. Partitioning also occurred at 3690–3660 Ma, when the 30–20 million years life of the c. 3700 Ma Isua proto-arc was terminated by juxtaposition with the c. 3800 Ma terrane that occurs along the south of the Isua supracrustal belt. The trace element chemistry for all the ≥3720–3700 Ma mafic to intermediate volcanic rocks indicates fluid-fluxing mantle melting. The c. 3690 Ma tonalites have signatures showing melting of garnet-bearing mafic (eclogite) sources. The Isua c. 3700 Ma assemblage developed at an intra-oceanic convergent plate boundary, and it has a life-cycle broadly analogous to (but not identical to) an oceanic island arc eventually accreted against older crust.

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Geological Society, London, Special Publications

Continent Formation Through Time

N. M. W. Roberts
N. M. W. Roberts
NERC Isotope Geosciences Laboratory, UK
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M. Van Kranendonk
M. Van Kranendonk
University of New South Wales, Australia
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S. Parman
S. Parman
Brown University, USA
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S. Shirey
S. Shirey
Carnegie Institution of Washington, USA
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P. D. Clift
P. D. Clift
Louisiana State University, USA
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Geological Society of London
Volume
389
ISBN electronic:
9781862396654
Publication date:
January 01, 2015

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