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Date of Award

2020

Document Type

Campus Access Master's Thesis

Degree Name

Master of Science in Geology (MS)

Administrative Home Department

Department of Geological and Mining Engineering and Sciences

Advisor 1

Chad D. Deering

Advisor 2

James M. DeGraff

Committee Member 1

Nadia Malaspina

DOI

10.37099/mtu.dc.etdr/1011

Abstract

The Bell Creek batholith, located in the Upper Peninsula of Michigan, lies on the southern edge of the Archean Superior Craton. The Paleoproterozoic batholith, exhumed during the Penokean Orogeny (1.89 Ga ago), exhibits amphibolite-facies metamorphism. This orogeny and subsequent deformation events have produced a complex suite of overprinting textural and mineralogical features previously not carefully examined. Consequently, significant uncertainty has existed about prior interpretations of the textural characteristics of Bell Creek rocks and their petrogenesis. Textural and compositional characteristics previously interpreted as metamorphic in origin are now interpreted to be primary igneous in origin. Such characteristics include: 1) flame-like and convoluted continuous banded structures, 2) almandine crystals in chemical equilibrium with micas in roundish xenoliths (clots), and 3) preferred alignment of K-feldspar megacrysts parallel to the orientation of banding manifested by biotite schlieren. Results presented here indicate that the Bell Creek batholith, a megacrystic S-type peraluminous granitoid, formed by melting amphibolite previously emplaced in the lower crust, followed by assimilation of mid to upper crustal-level metapelites. The chemistry of amphibole and plagioclase in the mafic units, together with field observations, reveals a component of mixing between the granitoid body and several generations of mafic intrusions.

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