SEISMIC REFLECTIONS AND ELECTRICAL-CONDUCTIVITY - A CASE OF HOLMES CURIOUS DOG

In the Purcell anticlinorium of the Canadian Cordillera, prominent upp er-crustal seismic reflectors and areas of high electrical conductivit y coincide over a wide area. Reflective layers traceable to outcrop an d to drill hole are caused mostly by impedance contrasts between Prote rozoic gabbroic sills and metasedimentary rocks. Layers with high elec trical conductivity are zones enriched in magnetic sulfide (probably p yrrhotite) within the sedimentary rocks. Attempts to interpret reflect ivity and high conductivity in terms of a single geologic process, alt hough tempting and certainly satisfying by appealing to Ocam's razor, must be done with care. We speculate that some explanations for crusta l reflectors and conductors may be unrealistic and propose an alternat ive paradigm of interlayered sills and (meta) sedimentary rocks rich i n high-conductivity minerals to explain both.