Perry, Eugene C., 1933-
M.S. (Master of Science)
Department of Geology
Geochemistry--Michigan--Marquette; Metamorphism (Geology)--Michigan--Marquette Region
Oxygen and carbon isotopic compositions of minerals were analysed for the rocks from the lowest grade metamorphic district of the Negaunee Iron Formation, Marquette, Michigan. Small scale variation of oxygen isotopic composition in quartz can be due to the contrast of quartz texture and/or the local mineralogical reaction: magnetite + CO₂ —> siderite + O₂. Isotopic patterns, carbonate content and texture suggest the above reaction occurred in some samples and was reversed in others. Carbon isotopic compositions of carbonate from Cascade core were found to be controlled by the carbonate/CO₂ ratio and, to a lesser extent, the carbon isotopic composition of CO₂ in regional metamorphic fluids, and have escaped from any modification by post-metamorphic hydrothermal fluids that were poor in carbon-bearing species. Oxygen isotopic fractionations of mineral pairs developed during regional metamorphism and have been reset near permeable zones fcy post-metamorphic fluids. Distinctly light oxygen of quartz immediately beneath a premetamorphic sill from Empire core is a relict effect of contact metamorphism as an analogue of the existence of anomalous grunerite reported by J. E. Gair (1975). Away iron the sill, oxygen isotopic fractionations developed in an externally controlled metamorphic fluid at a temperature lower than that of metamorphism by more than 100 ° C. It suggests that extensive retrograde metamorphism followed regional metamorphism when fluids were abundant. The isotopic data from the entire low grade metamorphic Negaunee Iron Formation consistently indicate that quartz is more resistant than carbonate in teras of oxygen isotopic exchange. A consistent isotopic temperature calculated from numerous three—dimensionally distributed samples suggests the metamorphic temperature for chlorite zone in this area was about 325 °C.
Shen, Shih-I., "Oxygen and carbon isotopic geochemistry of low-grade metamorphic Negaunee iron formation, Marquette, Northern Michigan" (1984). Graduate Research Theses & Dissertations. 4239.
vi, 70 pages
Northern Illinois University
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