The emergence of the Eoarchaean proto-arc: evolution of a c. 3700 Ma convergent plate boundary at Isua, southern West Greenland
Published:January 01, 2015
Allen P. Nutman, Vickie C. Bennett, Clark R. L. Friend, 2015. "The emergence of the Eoarchaean proto-arc: evolution of a c. 3700 Ma convergent plate boundary at Isua, southern West Greenland", Continent Formation Through Time, N. M. W. Roberts, M. Van Kranendonk, S. Parman, S. Shirey, P. D. Clift
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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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Continent Formation Through Time
The continental crust is our archive of Earth history, and the store of many natural resources; however, many key questions about its formation and evolution remain debated and unresolved:
What processes are involved in the formation, differentiation and evolution of continental crust, and how have these changed throughout Earth history?
How are plate tectonics, the supercontinent cycle and mantle cooling linked with crustal evolution?
What are the rates of generation and destruction of the continental crust through time?
How representative is the preserved geological record?
A range of approaches are used to address these questions, including field-based studies, petrology and geochemistry, geophysical methods, palaeomagnetism, whole-rock and accessory-phase isotope chemistry and geochronology. Case studies range from the Eoarchaean to Phanerozoic, and cover many different cratons and orogenic belts from across the continents.