Heat Flow and Tectonic Implications: Appalachian Ultradeep
Core-Hole
Site Area
J. K. Costain, E. R. Decker, L. Glover, III
Heat-flow determinations from four continuously cored shallow holes sampled
various rock types to be encountered in the ultradeep hole
, which will terminate
in Grenville basement. The heat flow in Grenville basement will be compared with
q*, which is believed to be the flux from the lower crust and upper
mantle. The deepest (400 m) shallow
hole
sampled biotite granite gneiss near
surface exposures of Grenville basement. Preliminary conductivity determinations
and geothermal gradients in the holes indicate an average heat flow of about 60
mW/m2 (1.4 HFU). The temperature at 10 km is not expected to exceed
180°C. Excellent reflections were recorded on regional seismic lines from the
crystalline rocks of the Inner Piedmont in the site area southeas of
Westminster. In addition, to the southeast in the crystalline Inner Piedmont, a
linear relation, q = q* + DA, between heat flow, q, and heat
generation, A, has been determined from cored holes in synmetamorphic and
postmetamorphic granitoids (slope, D = 7.8 km). Therefore, the heat-flow and
seismic data sets offer a unique opportunity to investigate the physical
significance of the linear relation and the possibility that granitoids are
tectonically truncated at a depth of about 8 km.
AAPG Search and Discovery Article #91043©1986 AAPG Annual Convention, Atlanta, Georgia, June 15-18, 1986.