Relationship of amphibole composition to host-rock geochemistry; the A-type gabbro-granite Wentworth Pluton, Cobequid shear zone, Eastern Canada

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doi: 10.1127/0935-1221/2007/0019-0029
Authors:Pe-Piper, Georgia
Author Affiliations:Primary:
Saint Mary's University, Department of Geology, Halifax, NS, Canada
Volume Title:European Journal of Mineralogy
Source:European Journal of Mineralogy, 19(1), p.29-38. Publisher: Schweizerbart'sche Verlagsbuchhandlung (Nägele u. Obermiller), Stuttgart, Federal Republic of Germany. ISSN: 0935-1221
Publication Date:2007
Note:In English. 24 refs.; illus., incl. 4 tables, geol. sketch map
Summary:The Wentworth pluton is the most alkaline of a series of Late Devonian metaluminous to mildly peralkaline plutons in the Cobequid shear zone. It includes numerous granitoid bodies of slightly differing composition, which may contain sodic, sodic-calcic or calcic amphiboles. This study examines the relative importance of host rock composition including volatiles, fO2, and temperature in controlling the type of amphibole present. Electron microprobe analyses and back-scattered electron images were used to characterize the amphiboles and whole-rock geochemical analyses were made from the host granites. Magmatic sodic amphiboles are arfvedsonite, ferrorichterite and katophorite. Ferrowinchite and riebeckite developed by subsolidus oxidation reactions with loss of fluorine. Sub-solidus changes in Fe-Ti oxides make reliable estimation of fO2 difficult. Regionally, sodic amphiboles are found only in the Wentworth pluton, suggesting the importance of peralkaline geochemistry and perhaps higher temperature as a result of voluminous gabbro in the pluton. However, the presence of sodic or calcic amphibole in granite with >73% SiO2 in the Wentworth pluton shows no systematic difference with either host-rock geochemistry or distance from the gabbroic heat source, except that rocks with sodic amphibole have high Li, suggesting abundance of free water.
Sections:Economic minerals and ore deposits; Geochemistry; Mineral data; Petrology; Topographical mineralogy
Subsections:Igneous rocks
Mineral Groups:Double-chain silicates
Subjects:A-type granites; Albitization; Alkali metals; Alkalic composition; Amphibole group; Anatexis; Arfvedsonite; Chain silicates; Chemical composition; Clinoamphibole; Devonian; Electron probe data; Fluorine; Gabbros; Geochemistry; Granites; Halogens; Hydrothermal alteration; Igneous rocks; Lithium; Magmatism; Metals; Metaluminous composition; Metasomatism; Mineral composition; Oxidation; Paleozoic; Peralkalic composition; Petrography; Plutonic rocks; Riebeckite; Silicates; Upper Devonian; Volatiles; Canada; Eastern Canada; Maritime Provinces; Nova Scotia; Cobequid shear zone; Oxygen fugacity; Wentworth Pluton
Coordinates:N452900 N453400 W0631000 W0635000
Abstract Numbers:07M/1073
Record ID:2007084264
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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