Windows into MORB Petrogenesis: Measuring U-Series Disequilibria in MORB from Transforms

这一建议为分析大洋中脊玄武岩样品中铀系列(U系列)不平衡提供了资金，这些玄武岩样品是在偏离大洋中脊的转换断层内喷发的。由于地幔熔体的混合在这个构造背景下相对于山脊轴不那么明显，来自变形的样品提供了一个窗口，可以观察到地球地幔熔融产生的玄武岩的多样性。U系列不平衡数据通过限制岩浆在地幔中的形成和上升的速度，包括定量固体上涌的速度，提供了研究熔融过程的能力。这笔赠款将用于从考克斯、布兰科、加勒特和西奎罗斯变换的25-30个样品中测定(230)/(238U)、(226Ra)/(230)和(231PA)/(235U)。这些数据将与来自大洋中脊相邻部分的补充性U系列数据以及常量和微量元素数据结合起来，以评估以下问题。1)转换位错引起的地幔冷却对地幔熔融有何影响？2)230~238U不平衡量与原始玄武岩的主要元素特征之间是否存在明显的关系？3)转换下的固体上涌速率是否与邻近的山脊轴有显著差异？对这些问题的回答将导致对大洋中脊玄武岩成因的综合看法的目标。

This proposal funds the analysis of uranium series (U-series) disequilibria in mid-ocean ridge basalt samples erupted within transform faults that offset mid-ocean ridges. Because mixing of mantle melts is less pronounced at this tectonic setting relative to the ridge axis, samples from transforms provide a window to observe the diversity of basalts produced by melting of the earth's mantle. U-series disequilibria data provide the ability to study the melting process by constraining the rate of formation and ascent of magmas through the mantle including quantification of the rate of solid upwelling. This grant will fund the determination of (230Th)/(238U), (226Ra)/(230Th) and (231Pa)/(235U) in 25-30 samples from the Cox, Blanco, Garrett and Siqueiros Transforms. These data will in turn be combined with complementary U-series data from adjacent portions of mid-ocean ridge and major and trace element data in order to evaluate the following questions. 1) What is the effect of mantle cooling due to transform offsets on how the mantle melts? 2) Is there an observable relationship between the amount of 230Th-238U disequilibria and the major element characteristics of primitive basalts? 3) Does the solid upwelling rate beneath the transform differ significantly from the adjacent ridge axis? Answers to these questions will lead toward the goal of providing an integrated view of the genesis of mid-ocean ridge basalt.