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

海底热液沉积在几分钟到数千年的时间尺度上形成，是从洋壳到海洋的大量热量和质量转移的产物，并与支持深海重要生命的活动一起形成。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间断形成，可以提供关于以下方面的重要信息：(1)海洋和结壳之间的能量和质量转移；(2)环境、物种形成率、幼虫扩散、能量和营养来源；以及(3)热液结构、地壳结构和结壳内热转移之间的关系。不幸的是，目前还没有可靠的方法来确定海底热液矿床的年代，以帮助我们限制其中一些主要过程。最有希望的方法包括测量238U和232Th衰减链中的同位素的放射性衰变。靶同位素(238U-234U-230Th-226Ra-210Pb-210Po；232Th-228Ra-228Th)的半衰期为138天至75kyr，样品的研究年限为~1~105年。这些时间尺度适用于地质上年轻的海底热液矿床。此外，这些同位素的应用特别适合于海底热液矿床中形成的矿物的年龄测定，因为地球化学过程分离出U系列和Th系列中的特定母子对，可利用这些母子对来获得年龄信息。进行这项研究的动机是，科学上需要一种可靠的方法来确定海底热液矿床的年代，并检验实现238U和232Th方法全部潜力所需的假设。这项研究将对热液过程的扎实了解与高精度的同位素测量结合在一起，以严格检验对充分开发分析方法和解释结果及其应用于海底热液喷口烟囱矿床至关重要的假设。目标将是确定该方法的实用性和局限性，并有望对未知年龄的热液喷口沉积物进行可靠的测年。对已知年龄的样品产生的数据，以及对未知年龄的其他样品的测量，将用于调查三个不同地点的热液作用的时间尺度。被选中进行分析的样品来自(1)跨大西洋地热系统(即TAG)；(2)新几内亚附近太平洋马努斯盆地的PACMANUS热液场；(3)西太平洋刘盆地的东刘扩张中心/瓦卢法脊。这项研究的更广泛影响包括为地质应用开发新的分析技术和年龄配对，对矿床形成的影响，公众宣传，以及向K-12教师、学生和普通公众广泛传播结果。对研究生的支持和对EPSCoR规定的机构(怀俄明州)的支持是其他影响。

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.