Exposed cross-sections through the continental crust: implications for crustal structure,petrology, and evolution |
| |
| Authors: | David M Fountain Matthew H Salisbury |
| |
| Institution: | 1. Deep Sea Drilling Project, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093 U.S.A.;2. Geological Research Division, Scripps Institution of Oceanography, University of California at San Diego, La Jolla, CA 92093 U.S.A. |
| |
| Abstract: | The continental crust is exposed in cross-section at numerous sites on the earth's surface. These exposures, which appear to have formed by obduction along great faults during continental collision, may be recognized by exposures of deep crustal rocks exhibiting asymmetric patterns of metamorphic grade and age across the faults and by distinctive Bouguer anomaly patterns reflecting dipping basement structure and an anomalously deep mantle. From an examination of five complexes which meet these criteria, it is concluded that the most prominent layering in the crust is not compositional but metamorphic. The lower crust consists of granulite facies rocks of mafic to intermediate composition while the intermediate and shallow levels consist predominantly of amphibolite facies gneisses and greenschist facies supracrustal rocks, respectively. Post-metamorphic granitic intrusions are common at intermediate to shallow levels. Position of discontinuities in refraction velocity, where present, commonly correspond to changes in composition or metamorphic grade with depth. The continental crust is characterized by lateral and vertical heterogeneities of varying scale which are the apparent cause of the complex seismic reflections recorded by COCORP. Field observations, coupled with geochemical data, indicate a complex evolution of the lower crust which can include anatexis, multiple deformation, polymetamorphism and reworking of older crustal material. The complexity of the crust is thus the result of continuous evolution by recycling and metamorphism through time in a variety of tectonic environments. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
