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

以前对蒙大拿州海伍德山省始新世钾质镁铁质火成岩的野外、岩石学和地球化学研究，已经确定了火山岩和侵入岩类型的分布，岩浆混合、分离结晶和脱气过程在岩浆演化中的重要性，以及在母岩浆的地幔源区存在古老的富集次大陆岩石圈和第三纪俯冲相关成分。该项目将通过对蒙大拿州第三纪各省的原始钾质到钙质岩浆岩进行详细的元素和同位素地球化学研究来扩大和扩大这项工作。重要的补充性研究将侧重于从几个省收集的下地壳和上地幔捕虏体的岩石学和地球化学。通过这项研究，应该可以相当详细地绘制蒙大拿州-怀俄明省下方古老的富集亚大陆岩石圈地幔的范围，直接确定深部地壳和地幔岩石圈的性质及其在岩浆成因中的作用，并批判性地评估有争议的构造模式，这些模式涉及美国西北部早第三纪的浅层俯冲。

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.