CONSTRAINTS ON THE EVOLUTION AND EMPLACEMENT OF THE BUCK CREEK COMPLEX AND OTHER BLUE RIDGE ULTRAMAFIC ROCKS, WITH IMPLICATIONS FOR OPHIOLITE EMPLACEMENT IN COLLISIONAL OROGENS
Sapphirine-bearing, spinel symplectites in the meta-troctolites suggest that Buck Creek rocks were largely anhydrous to ~800°C and ~0.9-1.1 GPa, conditions atypical of ophiolite emplacement. Limited hydration, mostly along contacts, took place near peak pressure conditions, possibly facilitating ductile disaggregation and emplacement of the body. Comparisons to the Zermatt-Saas ophiolite suggest rapid subduction of Buck Creek rocks to depths of ~ 30 km, where partial hydration, facilitated by prograde dehydration of surrounding rocks, aided in its emplacement into the subduction zone hanging wall.
Similar lithologies and prograde metamorphic assemblages in the nearby Lake Chatuge and Carroll Knob complexes point to comparable igneous origins and metamorphic histories, suggesting deep emplacement of oceanic rocks in a pre-Taconic subduction setting. By contrast, ultramafic and amphibolite bodies to the northeast in the Central Blue Ridge Cartoogechaye and Mars Hill terranes, including the Webster-Addie complex, differ compositionally, and record different metamorphic histories.