Cenozoic Magmatism of the Colorado Plateau

对科罗拉多高原渐新世至中新世Henry和La Sal山熔岩以及中新世至上新世San Rafael粗面玄武岩岩脉进行全面的地球化学分析，对于了解美国西部第三纪岩浆活动的构造背景和可能的壳幔相互作用至关重要。首先，俯冲作用是否在科罗拉多高原产生了渐新世-中新世岩浆作用？如果是的话，是什么不寻常的俯冲作用特征导致了稀疏的表层深成岩浆在距离板块边缘约1000公里的克拉通地壳中侵位？第二，最近的断言，从内华达州里诺延伸到圣胡安山脉(Sullivan，1987；Best，1988)的一条宽广的同时代东西岩浆带的时空连接的熔岩是否从地球化学基础上有效？青藏高原两侧的岩浆史在许多方面惊人地相似。一条宽阔的(1500公里)岩浆带几乎垂直于俯冲带，这在已知的地质史上将是前所未有的。第三，地幔岩浆和克拉通地壳如何在非裂谷环境中相互作用？长期以来，壳幔相互作用一直被认为是大陆弧的作用，但熔岩提供了一个在独特的背景下考虑岩石成因过程的机会。也许世界上很少有其他地区能够提供如此广泛的关于构造和相关成岩过程的关键信息。

A thorough geochemical analysis of the Oligocene to Miocene Henry and La Sal Mountains laccoliths, and Miocene to Pliocene San Rafael trachybasalt dikes of the Colorado Plateau is believed to be vital in understanding the tectonic setting and possible crust-mantle interactions of Tertiary magmatism in the western U.S. In particular, this study seeks support to address three key questions. First, did subduction produce the Oligocene-Miocene magmatism in the Colorado Plateau, and if so, what unusual characteristics of subduction resulted in the emplacement of sparse epizonal plutons in cratonic crust ~1000 km from the plate margin? Second, is the recent assertion that the laccoliths from a time space link for a broad, contemporaneous east-west magmatic belt extending from Reno, Nevada to the San Juan Mountains (Sullivan, 1987; Best, 1988) valid from a geochemical basis? The magmatic history of both sides of the Plateau is strikingly similar in many respects. A broad (1500 km) magmatic belt nearly perpendicular to the subduction zone would be unprecedented in known geologic history. Third, how do mantle derived magmas and cratonic crust interact in a non-rift environment? Crust-mantle interactions have long been considered for continental arcs, but the laccoliths provide an opportunity to consider petrogeneic processes in a unique setting. Perhaps few other areas in the world promise to yield such a wide range of critical information regarding tectonics and associated petrogenetic processes.