Two Buttes, CO., Mantle Evolution and Potassic Magmas

钾质火成岩的成因和次大陆地幔的演化将通过研究美国西部最东部的新生代火成岩侵入岩——科罗拉多州Two Buttes的钾质基性岩石来研究。这些岩石位于一个极端的地理位置，具有不寻常的成分，似乎位于厚厚的大陆根之上。将完成实地研究，确定年龄，并进行岩石学、电子探针、主要元素和微量元素以及同位素分析。主要元素和微量元素以及Nd和Sr同位素丰度将与不同构造背景下的岩石丰度进行比较，以检验岩浆成因、大陆岩石圈交代作用以及熔体生成与俯冲之间关系的理论。辉石的结构类似于岩浆混合的结构，同位素和化学研究将被用来调查在双Buttes和其他地方产生不同岩石类型的过程的重要性。

The genesis of potassic igneous rocks and the evolution of the subcontinental mantle will be investigated by studying the potassic, mafic rocks at Two Buttes, Colorado, the easternmost Cenozoic igneous intrusives in the western U.S. These rocks are at an extreme geographic position, have unusual compositions, and appear to be above a thick continental root. Field studies will be completed, ages will be determined, and petrographic, electron probe, major and trace element, and isotopic analyses will be made. Major and trace element and Nd and Sr isotope abundances will be compared with those of rocks in contrasting tectonic settings to test theories for magma genesis, for metasomatism of continental lithosphere, and for relationships between melt generation and subduction. Pyroxene textures resemble those ascribed to magma mixing, and isotopic as well as chemical studies will be used to investigate the importance of the process in producing the diverse rock types at Two Buttes and elsewhere.