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

海底热液沉积物的形成时间从几分钟到几千年不等，是海洋地壳向海洋大量热量和质量传递的产物，它的形成与深海中支持重要生命的活动相结合。了解这些沉积物形成的时间尺度，以及它们是连续形成还是偶然形成，可以提供以下重要信息：(1)海洋和地壳之间的能量和质量传递；(2)热液生物群落的环境、物种形成率、幼虫扩散、能量和营养来源；(3)热液结构、地壳结构与地壳内部传热的关系。不幸的是，目前还没有可靠的方法来确定海底热液沉积的年代，以帮助我们限制这些主要过程中的一些。最有希望的方法是测量238U-和232Th-衰变链中同位素的放射性衰变。目标同位素（238U-234U-230Th-226Ra-210Pb-210Po; 232Th-228Ra-228Th）的半衰期从138天到75年不等，并允许对样品进行1至105年不等的调查。这些时间尺度适用于地质上较年轻的海底热液矿床。此外，这些同位素的应用特别适合于测定海底热液矿床中形成的矿物的年代，因为地球化学过程在U-和Th-系列中分离出特定的父女对，可以利用这些父女对获取年龄信息。这项研究的动机是基于科学需要一种可靠的海底热液矿床测年方法，并测试实现238U-和232Th-方法的全部潜力所需的假设。本研究结合了对热液过程的深刻理解和高精度同位素测量，严格检验了对分析方法和结果解释及其在海底热液喷口烟囱沉积物中的应用的全面发展至关重要的假设。目标将是确定该方法的实用性和局限性，并希望能够对年龄未知的热液喷口沉积物进行可靠的定年。对已知年龄的样品所产生的数据，连同对未知年龄的额外样品的测量，将用于研究三个不同地点的热液过程的时间尺度。选择用于分析的样品来自(1)跨大西洋Geotraverse热液系统（即TAG）；(2)新几内亚附近太平洋马努斯盆地PACMANUS热液区；(3)西太平洋劳盆地的东劳扩张中心/ value Fa Ridge。这项研究的更广泛影响包括开发新的分析技术和地质应用的年龄对，对矿床形成的影响，公众宣传，以及向K-12教师、学生和一般公众广泛传播结果。对EPSCoR州（怀俄明州）的研究生和机构的支持是额外的影响。

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.