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Role of oceanic plateaus in the initiation of subduction and origin of continental crust

Rajeev Nair and Thomas Chacko
Role of oceanic plateaus in the initiation of subduction and origin of continental crust
Geology (Boulder) (July 2008) 36 (7): 583-586

Abstract

Archean tonalite-trondhjemite-granodiorite (TTG) magmatic suites represent the oldest coherent pieces of felsic continental crust. We present results of long-duration dehydration-melting experiments on amphibolites to show that melting depths of >48 km are required to have sufficient garnet in the residuum for generating the degree of heavy rare earth element (REE) depletion documented in Early Archean TTG. This depth constraint is inconsistent with early crust evolution models that posit melting at the base of oceanic plateaus or oceanic crust to explain the origin of Early Archean continental crust. Alternative explanations for this early crust, e.g., subduction models, are problematic in that they do not readily provide a mechanism for initiation of subduction in a hotter Archean Earth. We hypothesize that intraoceanic subduction systems in the Archean originated due to gravitational instabilities produced by compositional and density contrasts between converging oceanic plateau and normal oceanic lithosphere. Our model differs from earlier models of subduction initiation in that subduction of oceanic lithosphere occurs through the "hot" mantle residuum (protomantle lithosphere) at the base of newly formed oceanic plateau crust. Under a high Archean geothermal gradient, subducted oceanic crust would melt to produce TTG. This model explains the origin of subduction systems, TTG, TTG-mafic and/or ultramafic magma association, stabilization of continental crust, and the broadly coeval formation of cratons and their lithospheric roots.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 36
Serial Issue: 7
Title: Role of oceanic plateaus in the initiation of subduction and origin of continental crust
Affiliation: University of Alberta, Department of Earth and Atmospheric Sciences, Edmonton, AB, Canada
Pages: 583-586
Published: 200807
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 31
Accession Number: 2008-104114
Categories: Solid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2008137
Illustration Description: illus. incl. sect.
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200836
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