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Diversity in Earth's early felsic crust; Paleoarchean peraluminous granites of the Barberton greenstone belt

Cynthia J. M. G. Sanchez-Garrido, Gary Stevens, Richard A. Armstrong, Jean-Francois Moyen, Herve Martin and Regis Doucelance
Diversity in Earth's early felsic crust; Paleoarchean peraluminous granites of the Barberton greenstone belt
Geology (Boulder) (October 2011) 39 (10): 963-966

Abstract

Earth's oldest preserved granitoid crust dates back to the Paleoarchean and consists predominantly of sodic tonalite-trondhjemite-granodiorite (TTG) granitoids that arose through the partial melting of hydrated metabasalts. In contrast, granites (sensu stricto) typically appear relatively late in the plutonic record of the old cratons. However, the existence of Hadean zircons with mineral inclusion suites that are consistent with crystallization from peraluminous granitic magmas indicates that granitic rocks formed part of the earliest felsic crust; although we have direct evidence, this earliest felsic crust is not preserved. Here we present evidence of an unusual variety of markedly low-CaO, K (sub 2) O-rich, rutile-bearing, peraluminous granite and rhyolite that were produced concurrently with TTG magmas during three magmatic cycles in the Barberton Greenstone Belt (BGB), southern Africa. This material is not preserved as in situ rock units but occurs as clasts within a younger conglomerate. Within these rocks, plagioclase feldspar is a rare inclusion in zircon, relative to alkali feldspar, and has low anorthite contents (An < 15%), attesting to the primary nature of the low-Ca signature of the magmas. This, along with Eu/Eu* approximately 1, high K (sub 2) O and Sr content, as well as the peraluminous character of the magmas, is a consequence of phengite melting in a metagraywacke source at pressures in excess of those of plagioclase stability. This process contributed to each episode of continental crustal growth through the Paleoarchean to Mesoarchean in the BGB, despite leaving no plutonic record at the typical mid-crustal level of exposure that the TTG plutons around the belt represent.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 39
Serial Issue: 10
Title: Diversity in Earth's early felsic crust; Paleoarchean peraluminous granites of the Barberton greenstone belt
Affiliation: University of Stellenbosch, Center for Crustal Petrology, Matieland, South Africa
Pages: 963-966
Published: 201110
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 23
Accession Number: 2011-097153
Categories: Igneous and metamorphic petrologyStratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 2011282
Illustration Description: illus. incl. geol. sketch map
S26°00'00" - S26°00'00", E31°00'00" - E31°30'00"
Secondary Affiliation: Australian National University, AUS, AustraliaCentre National de la Recherche Scientifique, FRA, FranceUniversite Blaise Pascal, FRA, France
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: 201150
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