SGER: Melt Generation and Transport During Basalt Petrogenesis: Constraints from Measurements of 227Ac-231Pa Activity Ratios

铀系同位素为研究地幔玄武质岩浆成因的地球化学速率和过程提供了独特的视角。具体来说，最近的测量寿命较长的同位素的U-衰变系列放置了重要的限制熔化速率（与固体地幔上涌速率）和熔体分数。然而，有相对较少的测量寿命较短的铀衰变系列玄武岩样品中的同位素。因此，与时间相关的参数，如熔体传输速率和岩浆储存时间并不为人所知。为了更好地限制这些参数，在这个SGER奖，PI建议测量短寿命的227 Ac（t1/2 =21.8 y）在年轻的玄武岩样品从海洋中部扩张中心和板内火山，如夏威夷。这套地质年代学系统有可能成为一个重要的计时器，用于测定年轻洋中脊玄武岩的年龄，时间范围为10-100年。一种新的227 Ac计数技术的发展简化了其分析，使这项研究首次成为可能。

Uranium-series isotopes have provided unique insight into geochemical rates and processes during genesis of basaltic magma from the earth's mantle. Specifically, recent measurements of the longer-lived isotopes of the U-decay series have placed important constraints on melting rates (related to solid mantle upwelling rates) and melt fractions. However, there have been relatively few measurements of the shorter-lived isotopes of the U decay series in basaltic samples. As a result, time-dependant parameters such as melt transport rates and magma storage times are not well known. To better constrain these parameters, under this SGER award, the PIs propose to measure short-lived 227Ac (t1/2 =21.8 y) in young basaltic samples from mid-ocean spreading centers and intraplate volcanoes like Hawaii. This geochronologic system has the potential to be an important chronometer for dating of young mid-ocean ridge basalts in the time range of 10-100 years. Development of a new counting technique for 227Ac has simplified its analysis making this research possible for the first time.