SOUTHERN APPALACHIAN BLUE RIDGE (AND INNER PIEDMONT) GEOLOGY IN PRE- AND SYN-RAYMOND TIME

The modern era of understanding parts of the southern Appalachian Blue Ridge (BR) began in the 1960s to 1971 with publication of USGS Professional Papers 311, 349, and 615, based on high quality geologic mapping. The 1970 Cloos volume papers reflect the variable state of knowledge in different parts of the BR and Piedmont, particularly noticeable in syntheses and maps of large areas. Late 1960s–present-day detailed mapping projects have built large islands of knowledge of field relationships that, coupled with high quality geochemical data and modern age dates on monazite and zircons in basement, plutons, and metasedimentary rocks, have provided important knowledge about ages of different rock units, timing of metamorphism, and crucial detrital zircon data on the provenance of different terranes and recognition of new ones. Several terranes previously thought exotic are now known to be suspect or even “acquitted.” Without detailed mapping and modern geochronology, the Cat Square terrane and its timing of accretion and emplacement along the Brindle Creek fault would not be known; Tugaloo, Cartoogechaye, Milton, and others would not be confirmed as Laurentian. The oceanic-arc nature of the highly deformed and metamorphosed mafic-ultramafic complexes in the BR and Inner Piedmont would not be known without careful mapping and geochemical studies, to which Loren Raymond has made major contributions. Today, these new data have permitted us more precisely understand the southern Appalachian internides, but they also have defined new problems and fomented new controversies that should be resolved and additional new problems identified in the future, during post-Raymond time.