Classification of Altered Volcanic Island Arc Rocks using Immobile Trace Elements: Development of the Th Co Discrimination Diagram

Hastie, Alan Robert, Kerr, Andrew Craig ORCID: https://orcid.org/0000-0001-5569-4730, Pearce, Julian A. and Mitchell, S. F. 2007. Classification of Altered Volcanic Island Arc Rocks using Immobile Trace Elements: Development of the Th Co Discrimination Diagram. Journal of Petrology 48 (12) , pp. 2341-2357. 10.1093/petrology/egm062

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Abstract

Many diagrams conventionally used to classify igneous rocks utilize mobile elements, which commonly renders them unreliable for classifying rocks from the geological record.The K2O^SiO2 diagram, used to subdivide volcanic arc rocks into rock type (basalts, basaltic andesites, andesites, dacites and rhyolites) and volcanic series (tholeiitic, calc-alkaline, high-K calc-alkaline and shoshonitic), is particularly susceptible to the effects of alteration.However, by usingTh as a proxy for K2O and Co as a proxy for SiO2 it is possible to construct a topologically similar diagram that performs the same task but is more robust for weathered and metamorphosed rocks. This study uses 41000 carefully filtered Tertiary^Recent island arc samples to construct aTh^Co classification diagram. A‘testing set’comprising data not used in constructing the diagram indicates a classification success rate of c. 80%.When applied to some hydrothermally altered, then tropically weathered Cretaceous volcanic arc lavas from Jamaica, the diagramdemonstrates the presence ofa tholeiitic volcanic arc series dominated by intermediate^acid lavas overlain by a calc-alkaline series dominated by basic lavas.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Earth and Environmental Sciences
Subjects:	Q Science > QE Geology
Uncontrolled Keywords:	Island arc lavas ; Element mobility ; Discrimination plots; Jamaica ; Caribbean
ISSN:	0022-3530
Last Modified:	17 Oct 2022 10:15
URI:	https://orca.cardiff.ac.uk/id/eprint/7516

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