Abstract

“Is there any other point to which you wish to draw my attention?”

“To the curious incident of the dog in the night time.”

“The dog did nothing in the night time.”

“That was the curious incident,” remarked Sherlock Holmes.—Arthur Conan Doyle

In the Purcell anticlinorium of the Canadian Cordillera, prominent upper-crustal seismic reflectors and areas of high electrical conductivity coincide over a wide area. Reflective layers traceable to outcrop and to a drill hole are caused mostly by impedance contrasts between Proterozoic gabbroic sills and metasedimentary rocks. Layers with high electrical conductivity are zones enriched in magnetic sulfide (probably pyrrhotite) within the sedimentary rocks. Attempts to interpret reflectivity and high conductivity in terms of a single geologic process, although tempting and certainly satisfying by appealing to Occam's razor, must be done with care. We speculate that some explanations for crustal reflectors and conductors may be unrealistic and propose an alternative paradigm of interlayered sills and (meta)sedimentary rocks rich in high-conductivity minerals to explain both.

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