Probing the Structure of the Deep Continental Crust

Old, buried, deformed, crystalline rocks apparently make up most of the 40-kilometer-thick continental crust. This part of the earth is poorly explored and constitutes a major frontier of modern earth science. Two techniques, seismic reflection profiling and drilling, which were developed by industry for other purposes, offer special potential for such exploration. Seismic profiling of the deep crust by COCORP (the Consortium for Continental Reflection Profiling) has already produced important information, including evidence for extensive thin-skinned thrusting of older rocks over a continental margin as the corresponding ocean basin closed. Deep drilling of crystalline rocks of the continents for scientific purposes is so far relatively unexploited in the United States but is already being carried on elsewhere. In general, big science is likely to become more important in basic geology as this frontier is explored.