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GEOREF RECORD

Tectonic discrimination of granitoids

Papu D. Maniar and Philip M. Piccoli
Tectonic discrimination of granitoids
Geological Society of America Bulletin (May 1989) 101 (5): 635-643

Abstract

Granitoids as categorized by tectonic environment are (1) island arc granitoids (IAG), (2) continental arc granitoids (CAG), (3) continental collision granitoids (CCG), (4) postorogenic granitoids (POG), (5) rift-related granitoids (RRG), (6) continental epeirogenic uplift granitoids (CEUG), and (7) oceanic plagiogranites (OP). Of these, the IAG, CAG, CCG, and POG are considered orogenic granitoids, and the RRG, CEUG, and OP are considered anorogenic granitoids.The discrimination of granitoids is based on the major-element chemistry. Various discrimination plots are presented which sequentially discriminate the different tectonic environments. OP are separated from all other granitoids on the K (sub 2) O versus SiO (sub 2) plot. Discrimination between group I (IAG + CAG + CCG), group II (RRG + CEUG), and group III (POG) granitoids can be achieved by using plots of Al (sub 2) O (sub 3) versus SiO (sub 2) , FeO(T)/ [FeO(T) + MgO] versus SiO (sub 2) , and AFM and ACF ternary diagrams. In the figures, group I and group II plot in individual fields. Identification of group III is different, in that group III does not have a unique field in which it plots. Group III is identified because it consistently displays characteristics of both group I and group II. Further discrimination within group I can be accomplished on the basis of Shand's index. Only CCG have A/CNK [AL (sub 2) O (sub 3) /(CaO + Na (sub 2) O + K (sub 2) O)] values greater than 1.15. It is not possible to discriminate between IAG and CAG. Further discrimination within group II is done using the TiO (sub 2) versus SiO (sub 2) plot.The proposed discrimination scheme is applied to the Proterozoic granitoids of the midcontinent of the United States. It is shown that the Arbuckle granitoids are not anorogenic as previously thought.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 101
Serial Issue: 5
Title: Tectonic discrimination of granitoids
Affiliation: Univ. Pittsburgh, Dep. Geol. and Planet. Sci., Pittsburgh, PA, United States
Pages: 635-643
Published: 198905
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 97
Accession Number: 1989-032434
Categories: Igneous and metamorphic petrologyStructural geologyGeochemistry of rocks, soils, and sediments
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute.
Update Code: 1989
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