U-Pb geochronology and geochemistry of a portion of the Mars Hill terrane, North Carolina–Tennessee: Constraints on origin, history, and tectonic assembly
Published:January 01, 2004
Steven E. Ownby, Calvin F. Miller, Peter J. Berquist, Charles W. Carrigan, Joseph L. Wooden, Paul D. Fullagar, 2004. "U-Pb geochronology and geochemistry of a portion of the Mars Hill terrane, North Carolina–Tennessee: Constraints on origin, history, and tectonic assembly", Proterozoic Tectonic Evolution of the Grenville Orogen in North America, Richard P. Tollo, James McLelland, Louise Corriveau, Mervin J. Bartholomew
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The Mars Hill terrane (MHT), a lithologically diverse belt exposed between Roan Mountain, North Carolina–Tennessee, and Asheville, North Carolina, is distinct in age, metamorphic history, and protoliths from the structurally overlying Eastern Blue Ridge and underlying Western Blue Ridge. MHT lithologies include diverse granitic gneisses, abundant mafic and sparse ultramafic bodies, and mildly to strongly aluminous paragneisses. These lithologies experienced metamorphism in the granulite facies and are intimately interspersed on cm to km scale, reflecting both intrusive and tectonic juxtaposition.
Previous analyses of zircons by high-resolution ion microprobe verified the presence of Paleoproterozoic orthogneiss (1.8 Ga). New data document a major magmatic event at 1.20 Ga. Inherited and detrital zircons ranging in age from 1.3 to 1.9 Ga (plus a single 2.7 Ga core), ubiquitous Sm-Nd depleted mantle model ages ca. 2.0 Ga, and strongly negative εNd during Mesoproterozoic time all attest to the pre-Grenville heritage of this crust that was suggested by previous whole-rock Pb and Rb-Sr isotope studies. A single garnet amphibolite yielded a magmatic age of 0.73 Ga, equivalent to the Bakersville dike swarm, which cuts both the MHT and the adjacent Western Blue Ridge. Zircons from this sample display 0.47 Ga metamorphic rims. Zircons from all other samples have well-developed ca. 1.0 Ga metamorphic rims that date granulite-facies metamorphism. Silica contents of analyzed samples range from 45 to 76 wt%, reflecting the extreme diversity observed in the field and the highly variable protoliths.
The MHT contrasts strikingly with basement of the adjacent Eastern and Western Blue Ridge, which comprise relatively homogeneous, 1.1 to 1.2 Ga granitic rocks with initial εNd values near 0. It appears to have more in common with distant Paleoproterozoic crustal terranes in the Great Lakes region, the southwestern United States, and South America.