Melt Generation Beneath the Colorado Plateau and its Transition Zones

地球科学家面临的一个基本挑战是了解与板块边界无关的火山活动的起源，特别是与大陆内部无关的火山活动。火山岩化学提供了一种最有力的方法来探索这种活动的来源和融化机制，同时，对大陆目前的结构和动力学有深入的了解。这笔拨款支持了一项国际合作，该合作将对美国西南部的岩浆生成产生新的地球化学限制，那里有许多年轻的火山，在广阔的地理区域对大陆及其下层地幔进行采样。基于这些结果的解释将在以地球物理学为基础的持续努力（如Earthscope）的背景下得到完善，以获得与科罗拉多高原及其过渡带相关的火山活动的内部一致模型。尽管人们努力了解美国西南部大陆玄武岩的起源，但对于熔融发生的方式和地点，不同的观察和解释仍然存在。在许多情况下，现有的数据要么太零碎，要么太笼统，无法确定地幔是否在积极上涌，以及在哪里上涌，熔体分离的深度，以及地幔岩石圈在熔体产生中所起的化学和物理作用。该项目将对科罗拉多高原及其过渡带的年轻玄武岩进行全面的化学和Th-Hf-Nd同位素表征。基于配对的微量元素和同位素特征以及主元素数据反演的推断将划定熔融的深度和深度间隔以及富集和贫源的相对贡献。这些限制，以及对熔体组分大小的限制，将使我们更好地理解美国西南部岩石圈的结构和演化与熔体动力学之间的关系

A fundamental challenge for earth scientists is to understand the origin of volcanic activity not associated with plate boundaries and especially that interior to the continents. Volcanic rock chemistry provides one of the most powerful ways to probe the sources and melting mechanisms responsible for this activity and, at the same time, to gain insights into the present structure and dynamics of the continents. This grant supports an international collaboration that will produce new geochemical limits on magma generation beneath the southwestern U.S. where numerous young volcanoes sample the continent and its underlying mantle over a broad geographical region. Interpretations based on these results will be refined in the context of ongoing geophysics-based efforts such as Earthscope to arrive at internally consistent models for volcanic activity associated with the Colorado Plateau and its transition zones. Despite efforts to understand the origin of continental basalts in the southwestern U.S., disparate observations and interpretations persist for how and where melting occurs. In many cases, existing data are too piecemeal or too general to determine if and where the mantle is actively upwelling, the depths at which melts segregrate, and the chemical and physical role that mantle lithosphere plays in melt generation. This project will result in a comprehensive chemical and Th-Hf-Nd isotope characterization of young basalts from the Colorado Plateau and its transition zones. Inferences based on paired trace element and isotopic characteristics and from inversion of major element data will delimit the depth and depth interval of melting and the relative contributions of enriched and depleted sources. These constraints, as well as limits on the sizes of melt fractions, will permit a better understanding of the relationship between the structure and evolution of lithosphere and melting dynamics in the southwestern U.S.