AMPHIBOLITES AND META-ULTRAMAFIC ROCKS POINT TO PETROGENETIC AND TECTONIC DIVERSITY IN THE CARTOOGECHAYE TERRANE

The Cartoogechaye Terrane defined by Hatcher and others (2005) includes granulite facies metasedimentary lithologies in which extensive olistostromal rocks have been reported (Raymond et al 1989). Its tectonic position on the hangingwall of the Hayesville Thrust is consistent with an interpretation as a deep portion of an ancient accretionary complex. Amphibolites with igneous origins and metamorphosed ultramafic rocks occur commonly in the terrane. Detailed examinations of several prominent Cartoogechaye mafic-ultramafic occurrences during the 1997-2001 Blue Ridge REU Site research program provide evidence for multiple modes of origin for the protoliths of these rocks.

Metamorphosed mafic-ultramafic complexes in the SW section of the terrane (Buck Creek, Carroll Knob, Lake Chatuge) share similar lithologies and lithologic relationships, interpreted as metamorphosed mafic cumulate sequences; and bulk chemistries and REE signatures consistent with igneous origins as Type 1 (oceanic) ophiolite sequences. In the NE part of the terrane amphibolites and ultramafic rocks occur as distinct and often separated podiform bodies enclosed by metasedimentary schists and gneisses. Geochemically many of the amphibolites are consistent with andesitic protoliths, and the ultramafic rocks include locally abundant pyroxene. Such rocks are similar to those seen in the upper plates of subduction systems, and are incorporated into accretionary melanges via subduction erosion. The occurrence of upper-plate block lithologies in the NE and lower-plate ophiolitic rocks to the SW may indicate different modes of development and emplacement for these segments of the Cartoogechaye terrane.