Collaborative Research: U and Th decay series dating of seafloor hydrothermal deposits

合作研究：海底热液矿床的 U 和 Th 衰变系列测年

• 批准号: 1260079
• 负责人: Kenneth Sims
• 金额: $ 20.91万
• 依托单位: University of Wyoming
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-08-01 至 2017-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1260079&HistoricalAwards=false
• 关键词: Collaborative; Research; Th; decay; series

Seafloor hydrothermal deposits form on time-scales of minutes to thousands of years, are products of significant heat and mass transfer from the oceanic crust to the oceans, and form in conjunction with activity that supports significant life in the deep-sea. Understanding time-scales over which these deposits form and whether they form continuously or episodically can provide important information about (1) energy and mass transfer between the ocean and crust; (2) environments, speciation rates, larvae dispersal, energy, and nutrient sources for hydrothermal biological communities; and (3) relationships between hydrothermal structure, crustal structure, and heat transfer within the crust. Unfortunately, there are currently no dependable methods to confidently date seafloor hydrothermal deposits to help us constrain some of these major processes. The most promising method involves measuring the radioactive decay of isotopes in the 238U- and 232Th- decay chains. The half-lives of target isotopes (238U-234U-230Th-226Ra-210Pb-210Po; 232Th-228Ra-228Th) range from 138 days to 75 kyrs, and allow investigation of samples ranging from ~1 to 105 years. These time-scales are appropriate for geologically young seafloor hydrothermal deposits. In addition, application of these isotopes is uniquely suited for dating minerals formed in seafloor hydrothermal deposits because geochemical processes isolate specific parent-daughter pairs in the U- and Th- series that can be exploited for age information. The motivation for this research is based on scientific need for a reliable method for dating seafloor hydrothermal deposits and to test the assumptions required for realization of the full potential of the 238U- and 232Th- method. This research combines a solid understanding of hydrothermal processes with high-precision isotopic measurements to rigorously test the assumptions that are central to full development of the analytical method and interpretation of the results and their application to seafloor hydrothermal vent chimney deposits. Goals will be to define the utility and limitations of the method and, hopefully, enable reliable dating of hydrothermal vent deposits of unknown age. The data produced on samples of known age, together with measurements of additional samples of unknown age, will be used to investigate the time-scales of hydrothermal processes at three distinct locations. Samples selected for analysis are in-hand and from (1) the Trans-Atlantic Geotraverse hydrothermal system (i.e., TAG); (2) the PACMANUS hydrothermal field in the Manus Basin in the Pacific Ocean near New Guinea; and (3) the Eastern Lau Spreading Center/Valu Fa Ridge in the Lau Basin of the western Pacific. Broader impacts of the study include the development of new analytical techniques and age pairs for geological applications, implications for ore deposit formation, public outreach, and broad dissemination of results to K-12 teachers, students, and the general public. Support of a graduate student and support of an institution in an EPSCoR stated (Wyoming) are additional impacts.

海底水热沉积物是在数分钟到数千年的时间尺度上形成的，是从海洋地壳到海洋的大量热量和质量转移的产物，并与支持深海寿命的活动结合形成。了解这些沉积物形成的时间尺度以及它们是否连续或情节形成可以提供有关（1）海洋与地壳之间的能量和传质的重要信息； （2）水热生物群落的环境，物种率，幼虫分散，能量和营养来源； （3）地壳内的水热结构，地壳结构和传热之间的关系。 不幸的是，目前没有可靠的方法可以自信地与海底热液沉积物约会，以帮助我们限制其中一些主要过程。最有前途的方法涉及测量238U-和232衰减链中同位素的放射性衰减。目标同位素的半衰期（238U-234U-230th-230th-226ra-210pb-210po; 232th-228ra-228th）范围从138天到75 kyrs，并允许研究〜1至105年的样品。这些时间尺度适用于地质年轻的海底水热沉积物。此外，这些同位素的应用非常适合在海底热液沉积物中形成的约会矿物，因为地球化学过程隔离了可以利用年龄信息的U-和TH系列中特定的父母成对。这项研究的动机基于科学需求对可靠的约会海底水热沉积物的可靠方法，并测试实现238U-和232th方法的全部潜力所需的假设。 这项研究结合了对水热过程的扎实理解与高精度的同位素测量，以严格测试对分析方法充分发展的核心和对结果的解释及其在海底水热烟囱沉积物中的应用。目标将是定义方法的效用和局限性，并希望能够对未知年龄的水热矿床进行可靠的日期。在已知年龄样本上产生的数据，以及对未知年龄的其他样品的测量，将用于研究三个不同位置的热液过程的时间量表。选择进行分析的样品是手中的，并且来自（1）跨大西洋地理水热系统（即标签）； （2）在新几内亚附近的太平洋曼努斯盆地的Pacmanus热液场； （3）在西太平洋劳盆地的东部劳扩散中心/Valu Fa Ridge。该研究的更广泛的影响包括开发新的分析技术和用于地质应用的年龄对，对矿石存款形成的影响，公共宣传以及对K-12教师，学生和公众的结果广泛传播。在EPSCOR所说的（怀俄明州）中对研究生的支持和机构的支持是其他影响。