Cenozoic Magmatism of the Colorado Plateau

对科罗拉多高原渐新世至中新世Henry和La Sal山脉的泥质岩脉，以及中新世至上新世San Rafael的玄武岩岩脉进行全面的地球化学分析，被认为对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，俯冲作用是否产生了科罗拉多高原渐新世-中新世岩浆活动？如果是这样，那么哪些不寻常的俯冲特征导致了距离板块边缘约1000 km的克拉通地壳中稀疏的表向岩体侵位？第二，最近的断言，从地球化学的角度来看，从内华达州里诺延伸到圣胡安山脉的一个广泛的同时期东西岩浆带（Sullivan, 1987; Best, 1988）的时间和空间联系是否有效？青藏高原两侧的岩浆历史在许多方面惊人地相似。在已知的地质历史中，一条几乎垂直于俯冲带的宽（1500公里）岩浆带将是前所未有的。第三，在非裂谷环境下，幔源岩浆与克拉通地壳如何相互作用？长期以来，地壳-地幔相互作用一直被认为是大陆弧的原因，但这些漆膜岩提供了一个在独特环境下考虑岩石形成过程的机会。也许世界上很少有其他地区有望提供如此广泛的关于构造和相关岩石成因过程的关键信息。

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.