K. K. Tuftee

Publication Date

1981

Document Type

Dissertation/Thesis

First Advisor

Ervin, C. Patrick

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Geology

LCSH

Gravity--Wisconsin; Geology--Wisconsin; Geomagnetism--Wisconsin

Abstract

Geophysical investigations of the Precambrian rocks of Wisconsin are made imperative by the ubiquitous cover of glacial and postglacial deposits. Detailed gravity and aeromagnetic data of north-central Wisconsin serve to distinguish an Early Precambrian gneissic terrane, Middle Precambrian metamorphosed mafic and felsic volcanic rocks, and the products of Late Precambrian volcanism and plutonism. The Middle Precambrian metavolcanic zone in the northern part of the study area is characterized by alternating positive and negative Bouguer gravity anomalies and low intensity magnetic anomalies of considerable relief that tend to be elongated northeasterly reflecting the structural grain of the rocks. Observed anomalies can be correlated with the different average densities and magnetic susceptibilities of mafic and felsic volcanic rocks. Theoretical two-dimensional gravity models reveal faulting, folding and intrusive bodies. The differing Precambrian terranes are identified by their dissimilar gravity and magnetic fields. Granite and other felsic intrusions are defined by broad, very negative (-70 mgal) gravity anomalies and areas of low magnetic intensity and many magnetic irregularities; higher density gneisses are associated with correspondingly more positive (-35 to -65 mgal) gravity values. Mafic volcanics (gabbro, metagabbro) are associated with positive gravity anomalies (-55 to -65 mgal) and both higher than average magnetic level and greater magnetic relief. Greenstones should appear as areas of low magnetic intensity (-400 to -500 gammas), low magnetic relief, and relatively positive gravity anomalies. Basic dikes appear as 'noses' or gradient breaks against the magnetic background.

Comments

Includes bibliographical references.||Includes illustrations and maps.

Extent

76 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

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