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，特别是大陆内部。 火山岩化学提供了一种最有力的方法来探测这种活动的来源和熔融机制，同时也可以深入了解大陆的当前结构和动力学。 这笔赠款支持一项国际合作，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内对大陆及其底层地幔进行采样。 根据这些结果作出的解释将在目前地球镜等以地球化学为基础的努力的范围内加以完善，以便为与科罗拉多高原及其过渡区有关的火山活动建立内部一致的模型。尽管人们努力了解美国西南部大陆玄武岩的起源，对于融化是如何以及在何处发生的，存在着不同的观察和解释。 在许多情况下，现有的数据过于零碎或过于笼统，无法确定地幔是否以及在何处活跃地上涌，熔体分离的深度，以及地幔岩石圈在熔体生成中所起的化学和物理作用。 该项目将对来自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。 根据成对的微量元素和同位素特征以及主要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化源的相对贡献。 这些限制，以及对熔融分数的大小的限制，将允许更好地了解美国西南部岩石圈的结构和演化与熔融动力学之间的关系。

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.