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Igneous and Metamorphic Petrology

Thin section of an olivine mineral. Olivine is one of the main constituents of the upper mantle.

Conventional field, petrological and mineralogical studies of igneous and metamorphic rocks need to be supplemented by major and trace element geochemistry and by isotope tracer studies (see Geochemistry and Geochronology subsections) to provide an adequate chemical description of the rocks.
With these additional geochemical data, it is possible to characterize the geochemistry of the tectonic setting in which the granitic and volcanic rocks were formed. It is particularly important to capitalize on exposures of lower crustal rocks by undertaking petrological and geochemical studies to elucidate lower crustal petrogenesis (i.e., the processes by which rocks in the lower crust formed).

Pressure and temperature data from metamorphic mineral assemblages and their fluid inclusions are being used to estimate rates of uplift and erosion. This may be achieved by comparing P-T (pressure-temperature) data for the time the rocks were originally metamorphosed with P-T data for the time the same rocks were known to be at a higher crustal level (calibrated, for example, from the time when subsequent granitic plutons or basic dykes intruded them) and finally from the time the rocks were brought to the surface and made available to erosion. Complicated? You bet! But, this kind of information not only reveals the rate at which crustal thickening and subsequent uplift took place but also suggests further lines of inquiry regarding the subsidence histories of sedimentary basins which received the products of erosion related to the uplift of the metamorphic terranes.

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