Cocorp and the continental crust

Abstract

This is a speculative paper on the continental crust, a major frontier of modern earth science. Seismic reflection profiling data from the COCORP project, coupled with other kinds of geophysical and geological observations, suggest some fresh perspectives on the crust. For example, there is evidence for great differences within the basement at a single site and from one COCORP site to another. A simple layered model is surely not an adequate representation of the crust in most areas. There is, however, the puzzling and rather common occurrence of limited zones of parallel, though not always flat, layered features at various depths in certain parts of the crust. Are the corresponding rocks metasedimentary? Or igneous? Or both? There are transparent zones from which little or no coherent reflected seismic energy is detected. Are the corresponding rocks intrusions? Or highly deformed metasediments? Can degree of deformation suggest whether rocks were deformed in the hanging wall or footwall of a thrust? There is evidence for large‐scale thrusting and related features that emphasizes the great importance of the Wilson cycle to continental tectonics and that raises the possibility that water and rocks of sedimentary origin are trapped deep in the crust by the thrusting process and remain there for long periods with a variety of possible rheological and petrological consequences. In some places the modern Moho and adjacent rocks may correspond to parts of former oceanic or continental margin sections that have been emplaced at depth as a result of thrusting. The widely held concept of the Moho as a consistent boundary that is everywhere similar and that always separates the same kinds of rocks may be a major barrier to further progress in understanding the continental crust.