Geochemical and pressure-temperature evolution of the continental lithosphere

点击翻译按钮获取中文摘要

The history of the Earth's interior involves transfer of energy and matter between the interior and the surface. Some of the evidence for this history is found in metamorphic rocks that formed at the margins of the continents where the plates collide, e.g, eclogites and blueschists. Other sources of evidence include pieces of rock (xenoliths) brought up from depth by volcanic eruptions and large scale granitic intrusions. My studies in the Canadian Cordillera and elsewhere involve field mapping and sampling of these rocks with laboratory studies including microscopy and chemical analyses of the rocks and minerals. The data are used in combination with calculations based upon experimental data to estimate the pressure and temperature at which the rocks formed. The estimation of the pressure and temperature at which these rocks form provides information on: (1) the depth in the Earth at which the rocks formed; (2) the amount of uplift and erosion required to get the rocks to the surface; and (3) the variation of temperature with depth in the Earth at the time of metamorphism. Some of the matter transferred from the interior includes hot, water-rich fluids and igneous melts. Estimation of the composition of these fluids and melts is part of the study. Thermodynamic calculations and stable isotope studies can be used to estimate the composition of these fluids and melts. Another important part of this study is the timing of the metamorphic and igneous events and this is accomplished by dating the minerals using radioactive isotopes. All of these studies can be integrated and produce a comprehensive interpretation of the geologic history of large volumes of the Earth's crust and upper mantle.