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S- to I- to A-type magmatic cycles in granitic terranes are not globally recurring progressions; the cases of the Cape granite suite of Southern Africa and central Victoria in southeastern Australia

J. D. Clemens and G. Stevens
S- to I- to A-type magmatic cycles in granitic terranes are not globally recurring progressions; the cases of the Cape granite suite of Southern Africa and central Victoria in southeastern Australia
South African Journal of Geology (April 2021) 124 (3): 565-574

Abstract

Recurring progression from S- to I- to A-type granites has been proposed for a subset of granitic rocks in eastern Australia. The wider applicability and the validity of this idea is explored using the Cape Granite Suite (CGS) of South Africa and the granitic and silicic volcanic rocks of central Victoria, in southeastern Australia. Within the CGS there is presently little justification for the notion that there is a clear temporal progression from early S-type, through I-type to late A-type magmatism. The I- and S-type rocks are certainly spatially separated. However, apart from a single slightly older pluton (the Hoedjiespunt Granite) there is no indication that the S- and I-type granites are temporally distinct. One dated A-type granitic sample and a syenite have poorly constrained dates that overlap with those of the youngest S-type granites. In central Victoria, the granitic magma types display neither a spatial separation nor a temporal progression from one type to another. All magma varieties are present together and were emplaced within a far narrower time window than in the CGS. Thus, a progression may or may not exist in a particular region, and the occurrence of such a progression does not hold true even in a part of southeastern Australia, which afforded the type example. Thus, the idea that, globally, there should be a progression from S- to I- to A-type magmatism is unjustified. The critical factor in determining the temporal relationship between granitic magmas of different types is probably the compositional structure of the deep crust in a particular region, a reflection of how the individual orogen was assembled. In turn, this must reflect significant differences in the tectonic settings.


ISSN: 1012-0750
EISSN: 1996-8590
Serial Title: South African Journal of Geology
Serial Volume: 124
Serial Issue: 3
Title: S- to I- to A-type magmatic cycles in granitic terranes are not globally recurring progressions; the cases of the Cape granite suite of Southern Africa and central Victoria in southeastern Australia
Affiliation: University of Stellenbosch, Department of Earth Sciences, Matieland, South Africa
Pages: 565-574
Published: 20210429
Text Language: English
Publisher: Bureau for Scientific Publications, Pretoria, South Africa
References: 26
Accession Number: 2021-043820
Categories: Igneous and metamorphic petrologyStructural geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 2 tables, geol. sketch maps
S39°00'00" - S34°00'00", E140°00'00" - E150°00'00"
Country of Publication: South Africa
Secondary Affiliation: GeoRef, Copyright 2021, American Geosciences Institute. Abstract, Copyright, Geological Society of South Africa. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 202130
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