Geochemical Characterization of Mantle Sources of Tertiary Potassic to Calcalkaline Volcanics and their Xenoliths Montana

点击翻译按钮获取中文摘要

Previous field, petrologic and geochemical studies of the Eocene potassic mafic igneous rocks of the Highwood Mountains province, Montana have established the distribution f volcanic and intrusive rock types, the importance of magma mixing, fractional crystallization and degassing processes i magma evolution, and the existence of ancient enriched subcontinental lithosphere and Tertiary subduction-related components in the mantle source regions of the parent magmas. This project will amplify and extend this work by detailed elemental and isotopic geochemical studies of primitive potassic to calcalkaline magmatic rocks from throughout the Tertiary provinces of Montana. Important complementary studies will focus on the petrology and geochemistry of lower crustal and upper mantle xenoliths which have been collected from several provinces. From this research it should be possible to map the extent of ancient enriched subcontinental lithospheric mantle beneath the Montana-Wyoming province in considerable detail, to determine directly the nature of the deep crust and mantle lithosphere and their roles in magma genesis, and to critically evaluate controversial tectonic models which involve shallow subduction in the northwestern U.S. during the early Tertiary.