Collaborative Research: Combined Cathodoluminescence Microscopy and Silicate Microsample Sr Isotopic Studies of Paleogroundwater Hydrology in the Western United States

合作研究：结合阴极发光显微镜和硅酸盐微样品锶同位素研究美国西部古地下水水文

• 批准号: 0537997
• 负责人: Lang Farmer
• 金额: $ 11万
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-03-15 至 2009-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0537997&HistoricalAwards=false
• 关键词: Collaborative; Research; Combined; Cathodoluminescence; Microscopy

Intellectual merit: This project aims to evaluate the utility of Sr isotopic data from low-T silicate alteration phases in continental igneous and sedimentary rock as tracers for paleogroundwater hydrology, specifically tracking the distribution and timing of paleogroundwater flow. Cathodoluminescence petrography, physical microsampling, TIMS Sr isotopic, and oxygen isotope analyses will be combined to characterize secondary adularia formed during Tertiary low-T (200 C) fluid flow events in the western U.S. Two Tertiary volcanic suites were selected for study: the K-metasomatized Lemitar Tuff in southern New Mexico and K-metasomatized Tertiary volcanic rocks in the Harcuvar Mountains in western Arizona. The data for adularia precipitated from migrating fluids will be used to identify fluid events, and to understand the origin the fluids and the geometry of their pathways (e.g., whether they were density driven and related to the formation of closed basin brines, or meteoric fluids driven and related to the formation of surface topography during early Basin and Range extension). Preliminary studies of the Upper Lemitar tuff reveal that the metasomatizing fluids were isotopically distinct both from the phenocryst feldspars replaced by secondary adularia and from the tuff matrix, and so must have been derived from sources external to the tuff. Sr isotopic data are consistent with local Precambrian granitic source rocks and support models in which K-metasomatizing fluids were topographically driven meteoric waters. Further studies will test this hypothesis through Sr and O isotopic analyses of local Precambrian basement rocks, evaporitic minerals, and microsample analyses of adularia, matrix and other primary mineral phases within the Upper Lemitar Tuff. Lateral variations in fluid Sr isotopic compositions due to rock/water interactions along fluid pathways will be evaluated by sampling transects. Similar studies are planned for the Harcuvar Mountains. A third project involves microsampling and analysis of secondary cements and diagenetic phases within surface and well samples of arkoses from the Penn/Permian Fountain Formation (central Colorado); the goal is to investigate fluid interactions with these sediments. Broader impacts: This project involves a novel use of Sr isotopic data for paleohydrologic investigations, that if successful, could have wide applicability in many regions. This project will also provide an introduction to research methodology to undergraduates at Beloit College, who will conduct research activities both at their home institution and at the University of Colorado, Boulder. The project is planned as a joint research activity between the two institutions, with undergraduates being introduced to various laboratory techniques and their applications.

智力优势：本项目旨在评估大陆火成岩和沉积岩低t硅酸盐蚀变相Sr同位素数据作为古地下水水文示踪剂的效用，特别是跟踪古地下水流动的分布和时间。将结合阴极发光岩石学、物理显微采样、TIMS Sr同位素和氧同位素分析来表征美国西部第三纪低t（200℃）流体流动事件中形成的次生adularia，选择两个第三纪火山套进行研究：新墨西哥州南部的k -交代Lemitar凝灰岩和亚利桑那州西部Harcuvar山脉的k -交代第三纪火山岩。从迁移流体中析出的次生流体数据将用于识别流体事件，并了解流体的起源及其通道的几何形状（例如，它们是由密度驱动的，与封闭盆地盐水的形成有关，还是由盆地早期和山脉伸展期间的大气流体驱动的，与地表地形的形成有关）。对上莱米塔尔凝灰岩的初步研究表明，交代流体在同位素上既不同于次生adularia取代的斑晶长石，也不同于凝灰岩基质，因此可能来源于凝灰岩外源。Sr同位素数据与当地前寒武纪花岗质烃源岩和支持模式一致，其中钾交代流体为地形驱动的大气水。进一步的研究将通过对当地前寒武纪基底岩石、蒸发矿物的Sr和O同位素分析，以及对上莱米塔尔凝灰岩中adularia、基质和其他初级矿物相的微样品分析来验证这一假设。沿流体路径的岩石/水相互作用导致的流体Sr同位素组成的横向变化将通过采样样条进行评估。计划对哈库瓦尔山脉进行类似的研究。第三个项目涉及对宾夕法尼亚/二叠纪喷泉组（科罗拉多州中部）地表和油井样品中的次生胶结物和成岩阶段进行微观取样和分析；目的是研究流体与这些沉积物的相互作用。更广泛的影响：该项目涉及将Sr同位素数据用于古水文调查的新方法，如果成功，将在许多地区广泛适用。该项目还将为伯洛伊特学院的本科生介绍研究方法，他们将在自己的学校和科罗拉多大学博尔德分校进行研究活动。该项目计划作为两所院校的联合研究活动，向本科生介绍各种实验室技术及其应用。