CHALLENGES PRESENTED BY THE ASHE METAMORPHIC SUITE FOR RECONSTRUCTING THE TECTONIC HISTORY OF THE WESTERN NORTH CAROLINA SECTION OF THE SOUTHERN APPALACHIAN OROGEN

The Ashe Metamorphic Suite (AMS) of the Blue Ridge Belt consists of pelitic, quartzofeldspathic, metamafic, and metaultramafic rocks that underwent metasomatic metamorphism during Appalachian Orogenesis. The mafic-ultramafic rocks are most likely dismembered ophiolites as indicated by a number of petrochemical studies. Resolution of the petrotectonic history of western southern Appalachian Orogen in a way that accounts for Blue Ridge ophiolites and the enclosing AMS has remained enigmatic because of metamorphism, tectonic fragmentation of both the original stratigraphy and the metaultramafic bodies, and conflicting petrochemical and age data. Various types of data suggest that the AMS contains arc, back-arc, MORB, and slope to basinal sedimentary rocks. Mafic petrochemistries suggest MORB to OIB protoliths. Reconstructed sections of the ophiolitic rocks, data on spinel chemistries, and petrochemical data on metamafic rocks are consistent with the hypothesis that Blue Ridge ophiolites are fragmented, metamorphosed, very slow spreading ridge, Xigaze-type ophiolites, formed in a suprasubduction zone, back-arc setting. Deconstructing the orogen does not resolve the conflicts. To the west, Laurentia and the Sherwood, Grandfather, and Mars Hill terranes were sutured by the time of the Grenville Orogeny. To the east, the Cat Square and Carolina terranes were telescoped (perhaps repeatedly) and/or sutured with Laurentia during the Paleozoic Era. The intervening Toe (arc-back arc), Dahlonega (arc), and Inner Piedmont Tagaloo terranes were amalgamated with Laurentia during the Taconic Orogeny. Strike-slip faulting associated with transpression contributed to terrane amalgamation. The Ashe -Dahlonega relationship, the AMS petrotectonic setting, and the details of AMS deformation and metamorphism remain to be fully resolved. Clearly, the Allegheny Orogeny imposed large scale transport, uplift, and retrograde metamorphism, followed by broad scale folding of thrust faults and rock units, culminating that orogeny in North Carolina.