Chlorine Isotope Geochemistry of Altered Oceanic Crust: Empirical and Experimental Observations

改变的洋壳的氯同位素地球化学：经验和实验观测

• 批准号: 0946686
• 负责人: Jaime Barnes
• 金额: $ 24.89万
• 依托单位: University of Texas at Austin
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-03-15 至 2014-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0946686&HistoricalAwards=false
• 关键词: Chlorine; Isotope; Geochemistry; Altered; Oceanic

Intellectual Merit. Because of its strong partitioning into aqueous fluids, Cl and its isotopes (37Cl and 35Cl) are potentially powerful tracers of volatile and fluid migration in the crust and subduction zones, as well as the interaction between oceanic lithosphere and seawater derived hydrothermal fluids. To advance the utility of these tracers knowledge of its distribution and isotopic fractionation within various reservoirs is required. Recent work has begun to define the d37Cl values of various global Cl reservoirs (sediments, pore fluids, serpentinites), but isotopic data is very limited for one of the largest reservoirs, altered oceanic crust (AOC). AOC hosts ~2.5-3 x 10^12 g of Cl subducted worldwide, yet only three d37Cl values are published. Also, calculations and laboratory experiments imply minor fractionation between Cl-bearing phases, so it is commonly assumed that Cl faithfully records the isotopic composition of the hydration source. However, theoretical calculations use partition function ratios for divalent chlorides as analogues for silicates and fractionation experiments are limited to coexisting vapor, liquid, and precipitated salts in the H2O-NaCl and HCl systems. To properly address isotopic fractionation in systems for which Cl is a fluid tracer, experiments are needed for the common Cl-bearing silicate minerals in AOC (e.g., hornblende, actinolite, chlorite). Such information will enable better assessment of isotopic fractionation during fluid-rock and fluid-melt interactions and aid in interpreting Cl isotope data in general. The proposed research includes [1] a survey of d37Cl values for altered basalt and gabbro samples from DSDP/ODP/IODP drill cores, and [2] experimental determination of Cl isotope fractionation factors between the aforementioned hydrous silicate minerals and aqueous chloride solutions (seawater and brine). These complementary efforts are needed to fingerprint chlorine sources and accurately interpret data from natural samples. Ultimately, Cl isotope data will be incorporated into mass balance calculations to better understand material recycling at subduction zones.Broader impacts. PI Barnes is a first year assistant professor at UT-Austin. This proposal will partially fund one Ph.D. and one M.S. student. The proposed research will provide a foundation as Barnes begins her faculty career and will be integrated into the development of her new stable isotope lab. Two undergraduates will be partnered with the graduate students involved in this project, resulting in two honors theses. Co-PI Gardner is an associate professor at UT-Austin and will serve as a mentor to the newly hired Barnes. Both PIs will oversee and mentor students with laboratory work and data interpretation.

智力优点。由于其强大的分配到水性流体中，CL及其同位素（37CL和35CL）是地壳和俯冲区域中挥发性和液体迁移的潜在强大示踪剂，以及海洋岩石圈和海水衍生的水热液的相互作用。为了促进这些示踪剂的效用，需要在各种储层内进行分布和同位素分馏。最近的工作已经开始定义各种全球CL储层的D37CL值（沉积物，孔隙流体，蛇纹石），但同位素数据在最大的储层之一中受到了限制，它改变了海洋壳（AOC）。 AOC在全球范围内托管〜2.5-3 x 10^12 g的Cl俯冲，但仅发表了三个D37Cl值。 同样，计算和实验室实验意味着含Cl的阶段之间的分馏很小，因此通常假定CL忠实地记录了水合源的同位素组成。然而，理论计算使用分区功能比例作为硅酸盐的类似物，分馏实验仅限于H2O-NACL和HCL系统中的蒸气，液体和沉淀盐。为了正确地解决CL是流体示踪剂的系统中的同位素分馏，需要实验AOC中常见的Cl含硅酸盐矿物质（例如，Hornblende，statlenlite，statolite，氯酸盐）。 这样的信息将在流体岩石和流体融合相互作用期间更好地评估同位素分馏，并有助于解释CL同位素数据。拟议的研究包括[1]对DSDP/ODP/IODP钻核改变的D37CL值的调查，以及[2]在上述液态硅酸盐矿物质和水溶液溶液（海水和碳水化合物）之间的CL同位素分馏因子的实验确定[2]。需要这些互补的努力来指纹氯的来源，并准确解释天然样品的数据。最终，CL同位素数据将被纳入质量平衡计算中，以更好地了解俯冲带的材料回收。 Pi Barnes是UT-Austin的第一年助理教授。该提案将部分资助一家博士学位。和一米学生。拟议的研究将在Barnes开始她的教职生涯时为基金会提供基础，并将融入她新的稳定同位素实验室的发展。两名本科生将与参与该项目的研究生合作，从而获得两个荣誉论文。 Co-Pi Gardner是UT-Austin的副教授，将担任新雇用的Barnes的导师。 PI都将监督和指导学生实验室工作和数据解释。