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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.