The Border Ranges ultramafic and mafic complex, south-central Alaska; cumulate fractionates of island-arc volcanics

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doi: 10.1139/e85-106
Authors:Burns, Laurel E.
Author Affiliations:Primary:
Stanford Univ., Geophys. Dep., Stanford, CA, United States
Volume Title:Canadian Journal of Earth Sciences Revue Canadienne des Sciences de la Terre
Source:Canadian Journal of Earth Sciences = Revue Canadienne des Sciences de la Terre, 22(7), p.1020-1038. Publisher: National Research Council of Canada, Ottawa, ON, Canada. ISSN: 0008-4077
Publication Date:1985
Note:In English with French summary. 4 refs.; illus. incl. 5 tables, geol. sketch maps
Summary:This mafic-ultramafic zone (BRUMC) is composed of ultramafic cumulates, gabbronorite cumulates and massive gabbronorites. A very minor amount of tectonized ultramafic rock of mantle origin is present in the southern part. A thick sequence of andesitic volcanic rocks, the early Jurassic Talkeetna formation, lies north of and structurally above the mafic-ultramafic zone. Voluminous alkaline plutons composed of quartz diorite, tonalite and minor granodiorite intrude both the mafic plutonic complexes and the andesitic volcanic rocks. The cumulate ultramafic sections are largely composed of dunite + or - chromite, wehrlite, clinopyroxenite and websterite; they contain Fo90-81, with En45-50Fs1-7Wo45-49, En88-82Fs11-17 and chrome-rich spinels with a lack of plagioclase. The gabbroic sections comprise gabbronorites with = or <10-15% magnetite + or - ilmenite; hornblende is rare. Their relatively Fe-rich pyroxene, Fs6-13Wo45-40En81-63, and calcic plagioclase, An75-100, and their association with magnetite are common in plutonic xenoliths in island-arc rocks. The mineralogy and composition of the gabbroic rocks are consistent with the fractional crystallization products predicted to be associated with the formation of andesite from a basaltic magma. [J.M.H.]
Subjects:Complexes; Composition; Cumulates; Differentiation; Field studies; Fractional crystallization; Gabbros; Genesis; Igneous rocks; Intrusions; Island arcs; Mafic composition; Magmas; Mineral composition; Petrology; Plutonic rocks; Plutons; Ultramafics; Volcanism; Alaska; Chugach Mountains; Kodiak Island; United States; Border Ranges Complex; Gabbronorite; South-central Alaska; Southern Alaska; Southwestern Alaska
Coordinates:N612500 N621000 W1450000 W1483000
N570000 N583000 W1520000 W1540000
Abstract Numbers:86M/2460
Record ID:1985075210
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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