Scientific Drilling into the San Andreas Fault: Rare Gas 'Ages' of Matrix Fluids in Drill Core and Fluid Dynamics

该项目分析了SAFOD第三阶段岩心运行期间收集的基质流体样品，以使用Osenbrueck（1996年）开创并由该小组证明的已建立的惰性气体方法确定流入/流出断层带的流体[Stute等人，2005，2007，Ali等人，2007年，AGU和EarthScope摘要]。在SAFOD第三阶段取芯计划（2007年）期间，利用先前的NSF支持从岩心中采集了17个基质流体样品，将对这些样品的孔隙流体年龄、年龄梯度和基质流体的3 He/4 He同位素剖面进行评价。 这些结果将被解释为表明流入/流出SAFZ的流体的大小和方向。 基质流体的4 He和40 Ar“年龄”是水/岩石比、固相中的生产速率和释放到孔隙流体中的所产生的气体的分数的函数。本研究中测量的一套惰性气体同位素将用于分离非大气（产生和积累）和大气惰性气体成分。基本上，在岩心回收后，立即在现场去除回收岩心的外皮，并将中心的一小部分样品置于真空容器中。然后从容器中除去大气气体并密封容器。 稀有气体和基质流体目前正在从回收的样品中扩散出来。 在本项目执行过程中，将用质谱法确定释放到顶部空间的惰性气体，并按重量确定基质流体的总体积。固体中的稀有气体浓度也用于确定基质孔隙流体中过量稀有气体丰度的源函数和稀有气体从岩石中的释放。逐步加热实验将用于确定固相的扩散损失。 基质流体“年龄”和“年龄”梯度的计算将用于估计断层带内/附近流体输送的时间尺度和方向（输送时间尺度为10秒至100秒）。

This project analyzes matrix fluid samples collected during SAFOD Phase III core runs to determine the flow of fluids into/from the fault zone using established noble gas methodologies pioneered by Osenbrueck (1996) and demonstrated by this group [Stute et al.,2005, 2007, Ali et al., 2007, AGU and EarthScope abstracts]. The 17 matrix fluid samples obtained from drillcore collected with previous NSF support during the SAFOD Phase III coring program (2007) will be evaluated with regard to pore fluid ages, age gradients and 3He/4He isotopic profiles of matrix fluids. These results will be interpreted to indicate the magnitude and direction of fluid flow into/from the SAFZ. The 4He and 40Ar "age" of the matrix fluid is a function of the water/rock ratio, production rates in the solid phase and the fraction of produced gases released to the pore fluid. The suite of noble gas isotopes to be measured in this study will be used to separate non-atmospheric (produced and accumulated) and atmospheric noble gas components. Essentially, the outer rind of the recovered drillcore was removed on site immediately after core recovery and a small subsample from the center was placed in a vacuum container. Atmospheric gases were then removed from the container and the container was sealed. Noble gases and matrix fluids are currently diffusing out of the recovered sample. During the course of this project, the noble gases released to the headspace will be determined mass spectrometrically and the total volume of matrix fluid will be determined by weight. Noble gas concentrations in solids are also used to determine the source function for excess noble gas abundances in matrix pore fluids and the release of noble gases from the rock. Step heating experiments will be used to determine the diffusive loss from the solid phase. The calculation of the matrix fluid "age" and "age" gradient will be used to estimate the time scale and direction of fluid transport in/near the fault zone on the time scale of the transport (10s to 100s of years).