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Geology, Stratigraphic--Precambrian; Marquette County (Mich.)


ABSTRACT-The present study involved investigation of gneissic granite, migmatite, basic dikes, and faults in part of the Southern Complex of Michig.an. The average strike of the foliation of the gneissic granite based upon the orientation of feldspar phenocrysts is N. 60° w·;, the strike of the major dike set is between N. 30° W. and N. 60° W., the average strike of the fault zones-is N. 52° W., and a two-mile long body of migmatite trends about N. 57° W. The known history starts in the early Precambrian, when gneissic granite was emplaced and formed migmatites by incorporation of wall-rock material. Then the rocks were faulted, intruded by dikes, and regionally metamorphosed to the almandine amphibolite facies. After a second period of dike intrusion; hydrothermal solutions that p·assed upward through the fault and dike fissures caused retrograde metamorphism.

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