Publication Date

1981

Document Type

Dissertation/Thesis

First Advisor

Perry, E. C. (Eugene C.), 1933-

Degree Name

M.S. (Master of Science)

Department

Department of Geology

LCSH

Carbon--Isotopes||Oxygen--Isotopes||Isotope geology--Michigan||Geology--Michigan||Carbonate rocks

Abstract

Oxygen and carbon isotopic compositions were determined for rocks of the Negaunee Iron Formation of the Marquette Range Supergroup. The oxygen isotopic exchange among the silicates, oxides and fluid phases was shown to have reached equilibrium. Rock temperatures established from the quartz- magnetite oxygen isotopic fractionation geothermometry indicate an inhomogeneous geothermal state in the rocks of chlorite zone. The violation of a homogeneous geothermal state by permeability inhomogeneities is shown by the fact that the rocks with low temperature readings were universally limited to the pervious zones. Depletion of heavy oxygen in the decarbonated metamor- phic rocks was shown by a series of surface samples which covered almost the whole Negaunee Iron Formation. The escape of carbon dioxide which carried away the heavy oxygen is believed to be the main mechanism which caused the 0 de- pletion of these carbonated rocks. Bulk 0 content of rock systems in which decarbonation occurred is less than bulk 18 0 of rock systems in which decarbonation has not occurred. Both the heavy carbon and oxygen were found to be enriched in the carbonate collected from the pervious zones. This is shown to be the result of the following controls: 1. carbonate mineralogy 2. temperature variation 3. X[sub CO₂] change of the solution. In addition to the aforementioned parameters, the carbon isotopic variation of the rocks in the Negaunee Iron Formation was locally enriched by methane degassing in the rocks of low metamorphic grade whenever the mineral assemblage of carbonaceous material-quartz-ferrous silicate-magnetite is present. Mineralogy changes in a core provide an opportunity to establish temperature constraints based on quartz-magnetite oxygen fractionation temperature for the isograd-reaction: Siderite + 2 Minnesotaite = Grunerite + water + CO₂. The temperature for this reaction to proceed is determined to be 320° + 10°C under the conditions in which the oxygen fugacity is buffered by the mineral assemblage (carbonaceous material-quartz-magnetite-ferrous silicate) and the pressure is less than 3 kbar.

Comments

Includes bibliographical references.||Includes illustrations and maps.

Extent

72 pages, 6 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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