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The continental record and the generation of continental crust

Peter A. Cawood, C. J. Hawkesworth and B. Dhuime
The continental record and the generation of continental crust
Geological Society of America Bulletin (October 2012) 125 (1-2): 14-32

Abstract

Continental crust is the archive of Earth history. The spatial and temporal distribution of Earth's record of rock units and events is heterogeneous; for example, ages of igneous crystallization, metamorphism, continental margins, mineralization, and seawater and atmospheric proxies are distributed about a series of peaks and troughs. This distribution reflects the different preservation potential of rocks generated in different tectonic settings, rather than fundamental pulses of activity, and the peaks of ages are linked to the timing of supercontinent assembly. The physio-chemical resilience of zircons and their derivation largely from felsic igneous rocks means that they are important indicators of the crustal record. Furthermore, detrital zircons, which sample a range of source rocks, provide a more representative record than direct analysis of grains in igneous rocks. Analysis of detrital zircons suggests that at least approximately 60%-70% of the present volume of the continental crust had been generated by 3 Ga. Such estimates seek to take account of the extent to which the old crustal material is underrepresented in the sedimentary record, and they imply that there were greater volumes of continental crust in the Archean than might be inferred from the compositions of detrital zircons and sediments. The growth of continental crust was a continuous rather than an episodic process, but there was a marked decrease in the rate of crustal growth at ca. 3 Ga, which may have been linked to the onset of significant crustal recycling, probably through subduction at convergent plate margins. The Hadean and Early Archean continental record is poorly preserved and characterized by a bimodal TTG (tonalites, trondhjemites, and granodiorites) and greenstone association that differs from the younger record that can be more directly related to a plate-tectonic regime. The paucity of this early record has led to competing and equivocal models invoking plate-tectonic- and mantle-plume-dominated processes. The 60%-70% of the present volume of the continental crust estimated to have been present at 3 Ga contrasts markedly with the <10% of crust of that age apparently still preserved and requires ongoing destruction (recycling) of crust and subcontinental mantle lithosphere back into the mantle through processes such as subduction and delamination.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 125
Serial Issue: 1-2
Title: The continental record and the generation of continental crust
Affiliation: University of Saint Andrews, Department of Earth Sciences, Saint Andrews, United Kingdom
Pages: 14-32
Published: 20121031
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
Number of pages: unpaginated
References: 133
Accession Number: 2012-101447
Categories: Solid-earth geophysicsGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
Secondary Affiliation: University of Western Australia, AUS, AustraliaUniversity of Bristol, GBR, United Kingdom
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: 201252
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