GEOCHEMICAL ANALYSIS OF THE DICKINSON GROUP OF THE UPPER PENINSULA, MICHIGAN: A STUDY OF AN ACCRETED TERRANE OF THE SUPERIOR PROVINCE

The lithospheric development of North America is intimately linked to the evolution of the Superior Province. The Superior Province, an Archean age craton located to the north of Lake Superior, has been generated through the accretion of multiple terranes. The nature of the terranes associated with these accretion events is poorly constrained. The Dickinson group, located in central Dickinson County in the Upper Peninsula of Michigan, is largely a metasedimentary formation that includes mafic flow units and is cross cut by mafic dikes. The Dickinson group is composed of three primary stratigraphic units: the East Branch arkose, the Solberg schist, and the Six-Mile Lake amphibolites. Mafic dikes and flows within the East Branch arkose are the focus of this study. The East Branch arkose, which lies at the base of the Dickinson group, is bound by unconformities that place its age between 3.6 and 2.58 Ga. We have analyzed the major and trace element geochemistry of a suite of 20 samples collected from the Dickinson group and determined the dikes and flows to be of a transitional composition between olivine tholeiite and alkali-olivine basalt. In some instances there is a geochemical correlation between the flows and a subset of dikes. For other dikes there appears to be little correlation with the flows through which they pass suggesting temporal diversity in dike emplacement and heterogeneity in magma generation mechanisms. We explore the correlation between mafic units in the contemporaneous Minnesota River Valley terrane and the Dickinson group to examine accretionary processes along the southern margin of the Superior Province.