Abstract
Complexes occur in an arcuate chain within the Charlotte Belt of the Carolina Piedmont. Preliminary age dating suggests that metagabbros are 500 to 600 my old. Conditions of metamorphism for metagabbros were approx 500 degrees to 550 degrees C and 5 kb, appropriate to depths of 17 to 18 km. Crystallization ages for most gabbros determined by Sm/Nd are 399 to 407 my, though one petrologically distinctive pluton is older ( approximately 479 my). Gabbroic bodies are thick cylindrical or lopolithic intrusions emplaced at depths of 13 to 17 km. Crystallization sequences for their tholeiitic parental magmas were dominated by fractionation of olivine (or orthopyroxene), plagioclase, and clinopyroxene to produce ortho- and mesocumulates. Syenites are the end fractionation products associated with several gabbros. Irregular distributions and absence of layering may reflect either emplacement as crystal mushes, convective stirring, or multiple intrusive pulses. Tectonic control of the sites of magma generation and/or ascent. Features of these complexes are consistent with their formation at a compressional plate margin.--Modified journal abstract.
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