CRUSTAL STRUCTURE BENEATH THE CENTRAL NORTH CAROLINA-TENNESSEE BLUE RIDGE MOUNTAINS

The longevity of ancient orogenic features has been a geological conundrum for decades. Early papers (i.e. Ahnert, 1970) suggested that even accounting for isostatic uplift, orogenic relief should be reduced to 1 percent of its initial value in as little as 60 million years. The southern Appalachians last experienced tectonic uplift some 270 Ma, but still exhibit mean elevations of over 1 km, with the highest point (Mt. Mitchell) reaching slightly over 2 km. More recent work suggests that erosion rates on the order of 30 mm/Ky over the past 200 Ma have resulted in some 6 to 7 km of unroofing in the North Carolina-Tennessee mountains (Matmon et al, 2003). An important component to understanding how the southern Appalachians have maintained their topography over such extended time periods is the underlying crustal structure. While there have been a number of studies looking at crustal thickness in the southern Appalachians (i.e. Cook and Vesudevan, 2002, and references therein), none have succeeded in imaging the Moho across the entire range. We have deployed a small transect of six broadband seismometers across the Blue Ridge Mountains in North Carolina in order to constrain crustal and mantle lithospheric structures in the area. Of particular interest is the relationship between Moho depth and elevation: is the Appalachian orogen isostatically compensated or is there evidence for Cenozoic doming and dynamic uplift in the area. Preliminary receiver function results indicate a relatively thick crust (~45 km) beneath average elevations of ~1000 m. Further work modeling crustal structures and Vp/Vs ratios will help determine the nature of the support for the southern Appalachian orogen.