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

该提案为分析大洋中脊玄武岩样本中铀系列（U系列）不平衡提供了资金，这些样本是在偏移大洋中脊的转换断层内喷发的。 由于地幔熔体的混合是不太明显的，在这个构造环境相对于脊轴，样品从变换提供了一个窗口，观察地球的地幔熔融所产生的玄武岩的多样性。U系列不平衡数据提供了通过限制岩浆通过地幔的形成和上升速率（包括固体上涌速率的量化）来研究熔融过程的能力。 这笔赠款将资助测定来自考克斯、布兰科、加勒特和西凯罗斯变换的25-30个样品中的（230 Th）/（238 U）、（226 Ra）/（230 Th）和（231 Pa）/（235 U）。 这些数据又将与大洋中脊相邻部分的补充U系列数据以及主元素和微量元素数据相结合，以评价下列问题。1)转换偏移引起的地幔冷却对地幔熔化有什么影响？2)原始玄武岩的~（230）Th-~（238）U不平衡量与主量元素特征之间是否存在可观测的关系？3)转换层下的固体上涌速率与相邻脊轴有显著差异吗？ 这些问题的答案将导致对大洋中脊玄武岩的成因提供一个综合的看法的目标。

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.