HR: 0830h
AN: GP21A-0242 INVITED
TI: Lithospheric Architecture And Anisotropy Below The Southern Appalachians Compressional Orogen From Electrical Conductivity Structure
AU: * Wannamaker, P E
EM: pewanna@egi.utah.edu
AF: University of Utah/EGI, 423 Wakara Way, Ste 300, Salt Lake City, UT 84108
AU: Chave, A D
EM: alan@whoi.edu
AF: Woods Hole Oceanographic Inst., Dept of Geology and Geophysics, Woods Hole, MA
AU: Booker, J R
EM: booker@geophys.washington.edu
AF: University of Washington, Geophysics AK-50, Seattle, WA
AU: Jones, A G
AF: Geological Survey of Canada, 600 Booth St., Ottawa, ON Canada
AU: Unsworth, M J
AF: University of Alberta, Inst. of Geophysics, Edmonton, AB Canada
AU: Evans, R L
AF: Woods Hole Oceanographic Inst., Dept of Geology and Geophysics, Woods Hole, MA
AU: Ogawa, Y
AF: Tokyo Inst. of Technology, Volcanic Fluid Res. Center, Tokyo, Japan
AB: Fossil compressional terranes exhibit seismic shear-wave anisotropy with the fast direction typically parallel to strike. Anisotropy in electrical conductivity is being resolved also in such regimes, with the higher conduction direction usually parallel to strike as well. The Southern Appalachian orogen is a classical setting of diachronous terrane accretion, culminating in extensional collapse and finally opening of the modern Atlantic Ocean. In addition to anisotropy, basic tectonic issues here include the degree of transport of previous terranes by subsequent compressional events, the domain of underthrust sedimentary rocks, and the depth extent and physico-chemical state of fossil suture zones. The electrical conductivity structure of this orogen has been resolved to depths of 300-400 km in an MT transect extending from 600 km inland in the Cumberland Basin of eastern Kentucky to the Atlantic Ocean abyssal plain 1500 km offshore. This complements investigations here using potential fields and passive and active seismology. The Central Piedmont Suture (CPS) stands out as a strong conductor dipping steeply SE-ward to at least the middle crust caused probably by underthrust graphitic metasediments. Essentially no low-grade sedimentary rocks are evident below the Alleghanian thrust to the NW end of the transect. Conductivity along strike of the deep crust and upper mantle under the NW half of the transect is much higher than the minimun conductivity required across strike. The higher conduction direction also parallels the regional fast S-wave direction similar to other study areas. The greatest anisotropy in the NW underlies the New York-Alabama lineament, correlatable perhaps with the Grenville suture, and suggested to be due to deeply underthrust graphitic metasediments. The ocean bottom and SE-most land MT sites reveal a conductive electrical asthenosphere beneath the old ocean basin at a depth ~150 km, similar to seismic estimates, which persists landward to approximately the Carolina terrane. The uppermost mantle of the Paleozoic oceanic terranes on land SE of the CPS is much more resistive than corresponding Precambrian upper mantle to the NW of the CPS, and is interpreted as due to a Late Alleghanian delamination event. This area exhibits negligible seismic anisotropy.
DE: 0905 Continental structures (8109, 8110)
DE: 1515 Geomagnetic induction
SC: GP
MN: 2001 AGU Fall Meeting