SGER: Dating Volcanic Rocks Using Syngenetic Non-Silicate Minerals

在这一小笔勘探研究拨款(SGER)中，有人提议测试一种新的地质年代学技术，该技术基于共生非硅酸盐矿物的U系列不平衡来确定年轻熔岩流的年龄。由于硅酸盐晶体具有不同的岩浆停留时间，而且在许多情况下，没有必要的铀浓度和U/Th比率，以前用U系列同位素技术测定熔岩年龄的尝试一直是有问题的。拟议的分析计划将集中在矿物石膏上。石膏是玄武岩中常见的共生矿物，常见于熔岩管中。它们具有所需的高U和低Th浓度。关于石膏晶体的初步数据给出了令人鼓舞但喜忧参半的结果。这个SGER的最终目的将是制定一套标准，通过在适当的野外区域使用锶、硫以及在某些情况下的镭同位素数据来区分可测定日期的物质和不能测定日期的物质。这些最终将被用来记录和确定这种新技术对许多不同类型的岩石可行的可能性。如果成功，该项目的成果将在地球科学中具有广泛的适用性。

In this Small Grant for Exploratory Research (SGER), it is proposed to test a new geochronological technique based on U-series disequilibrium of cogenetic non-silicate minerals to date young lava flows. Previous attempts to dating lavas with U-series isotopic techniques have been problematic due to the fact that silicate crystals have variable magma residence times and, in many cases, do not have the requisite U concentration and U/Th ratios. The proposed analytical plan will be focused on the mineral gypsum. Gypsum is a common cogenetic mineral in basalts often found in lava tubes. They have the required high U and low Th concentrations. Preliminary data on gypsum crystals give encouraging but mixed results. The ultimate purpose of this SGER will be to develop a set of criteria to distinguish datable materials from those that are not by using strontium, sulfur and in some cases radium isotopic data in a suitable field area. These will be used eventually to document and establish the likelihood that this new technique is feasible for a number of different rock types. If successful, results from this project will have broad applicability in the Earth Sciences.