Brian Hirst

Publication Date

1976

Document Type

Dissertation/Thesis

First Advisor

Casella, Clarence J.

Degree Name

M.A. (Master of Arts)

Legacy Department

Department of Geology

LCSH

Geology--Montana; Geology; Stratigraphic--Precambrian; Geology--Wyoming

Abstract

Precambrian rock units mapped are the: 1) metamorphic complex, 2) Hellroaring Mountain quartz monzonite stock, 3) leuco quartz-tonalite sills and 4) diabase dikes and sills. The metamorphic complex is the oldest unit and con­sists of eastward-dipping quartz and mica-rich metasedi­ments. These include sparse metaconglomerate and amphibole schist. Plagioclase is common in all these rocks but potassium feldspar is absent. The earliest decipherable event (Dj) involved metamorphism and deformation of the sedimentary pile which produced the dominant N-S trending fabric. The deformation produced probable large-scale isoclinal folds with axial-plane mica foliation together with amphibolite grade metamorphism. Folding and meta­morphism were complex and polyphase in nature. The Hellroaring Mountain quartz monzonite stock intruded the metamorphic complex a minimum of 2,800 m.y. ago. The stock is mainly concordant and has shouldered aside the metamorphic complex. Thermal effects of the intrusion are confined to within several meters of the stock. Leuco quartz-tonalite and diabase probably intruded after the Hellroaring stock. Shearing accompanied by mild metamorphism is evident in the diabase and may represent a later Precambrian event.

Comments

Includes bibliographical references.||Includes illustrations and maps.

Extent

v, 76 pages, 2 unnumbered pages

Language

eng

Publisher

Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type

Text

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