AMPHIBOLITE FACIES METAMORPHISM OF TREMOLITE/ACTINOLITE-BEARING ULTRAMAFIC ROCKS FROM ROCKY RIDGE AND PEDEN ULTRAMAFIC BODIES OF THE ASHE METAMORPHIC SUITE, NC

The Blue Ridge Mountains of the Appalachian Range host a diverse selection of metamorphic rocks, including ultramafic rocks of ophiolite origin. The northeast-striking Rocky Ridge and Peden ultramafic bodies are part of the Ashe Metamorphic Suite, a disrupted ophiolite emplaced during the Taconic Orogeny, located in Northwest North Carolina.

The most common mineral assemblage is tremolite/actinolite, anthophyllite, and chlorite plus pyrite, ilmenite, or magnetite. Anthophyllite indicates amphibolite facies (<6 kbar and at least 650° C). Smaller matrix minerals are tremolite, chlorite, and anthophyllite while porphyroclasts are tremolite. Anthophyllite is typically euhedral and unaltered while tremolite is breaking down to chlorite. Anthophyllite grains are randomly oriented at high angles to the foliation defined by tremolite. Strain shadows of chlorite surround some tremolite porphyroclasts and fill in boudinaged tremolite. Large chlorite pseudomorphs formed after amphibole porphyroclasts, indicating a greenschist facies overprint. Some chlorite is crenulated and forms an S-C fabric with fine-grained amphiboles. These textures indicate multiple deformation events perhaps linked with different orogenies.

The surrounding mafic rock consists of schistose to gneissic hornblende, quartz, plagioclase, and epidote. This assemblage indicates amphibolite facies (>550° C) with a greenschist facies overprint (250°-500° C); these ranges suggest that the ultramafic and mafic bodies were subject to the same metamorphic events. These assemblages are present in both bodies and do not indicate a clear pattern of compositional layering.

The mineralogy and textural evidence within the Rocky Ridge and Peden bodies points towards multiple deformation events. The first event was Taconic emplacement into the continental crust, followed by Acadian and perhaps Alleghenian deformation events. This work more tightly constrains the deformation and metamorphism in the lower crust during orogeny.