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

铀系列同位素为地球化学速率和地幔玄武岩岩浆形成过程提供了独特的见解。具体来说，最近对u衰变系列的长寿命同位素的测量对熔化速率（与固体地幔上涌速率有关）和熔体分数提出了重要的限制。然而，对玄武岩样品中铀衰变系列的短寿命同位素的测量相对较少。因此，与时间有关的参数，如熔体输送速率和岩浆储存时间，并不为人所熟知。为了更好地约束这些参数，在SGER的授奖下，PIs们提议测量来自洋中扩张中心和像夏威夷这样的板内火山的年轻玄武岩样本中的短寿命227Ac （t1/2 =21.8 y）。该年代学体系有可能成为10-100年洋中脊年轻玄武岩定年的重要时计。一种新的227Ac计数技术的发展简化了它的分析，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.