Constructing a 1.5-million-year time series of magmatic and hydrothermal activity at the Juan de Fuca ridge

洋脊是地球上80%的火山活动的场所。这些特征排放二氧化碳，并通过深海温泉对海洋的化学成分施加重要控制。这些火山沿着6万公里长的洋脊系统排列，在洋脊系统中，板块分开形成海底。 对这些火山的研究一直局限于最近的火山活动，因为随着板块的扩张，火山被沉积物覆盖，变得难以接近。由于这个原因，现在有一个洋中脊火山活动的快照，但几乎没有可能研究它如何随着地球科学最重要的参数之一-时间而变化。 如果不了解地质现象随时间的变化，即所谓的"时间序列"，就无法理解地质现象的许多方面。 例如，气候的时间序列表明，地球进入和退出冰河时代，全球变暖正在发生。 新的发现现在允许通过沿垂直于洋脊的剖面沿着取沉积物芯来构建洋脊的时间序列。这些岩芯将用于研究沉积物中保存的火山玻璃。 特别是，时间序列将允许测试的假设，冰河时代的周期可能会影响到海洋中脊火山活动和相关的热液活动的周期。前往俄勒冈州和华盛顿海岸附近的胡安·德富卡海岭（Juan de Fuca ridge）的巡航将首次获得一百万年或更长时间的时间序列。该项目将为本科生参加研究巡航提供支持。此外，该项目将支助一次国际会议，并为在哈佛自然历史博物馆举办的一次博物馆展览作出贡献，欧洲研究理事会已为科学分析提供研究赠款，以便通过一项系统的取样方案，沿垂直于胡安·德富卡海岭的沿着进行取样，调查海岭过程的时间序列。ERC向四名主要调查人员（三名在德国的GEOMAR，一名在哈佛）提供的赠款不包括收集海上沉积物岩心的资金。该提案为获取必要样品的运输时间提供资金。使用自主式潜水器SENTRY进行的初步11天航程将获得沉积厚度和高分辨率测深数据，以指导取芯工作。 然后，21天的行程将在三个断面上进行70次取样，两次在山脊以西，距离山脊转换交叉点不同的距离，一次在东边。这次航行将产生第一个连续的、共同登记的0至1Ma时间尺度的玻璃成分、热液活动和水深测量的时间序列。由于海底迅速被沉积物覆盖，玄武岩被改变或钾含量低，因此无法获得洋脊玄武岩和沉积物成分的时间序列，从而造成测年问题。特别是104 - 106年的时间尺度对于检验大洋中脊的一系列假设至关重要，从构造/岩浆循环的存在和时间尺度，到岩浆房和热液系统的连续性，再到更新世以来冰川循环和海脊过程之间的可能关系。来自脊轴附近的岩心的初步数据表明，每个岩心可能保存50 - 100ka的时间序列的新鲜玻璃有趣的变化。将使用间隔紧密的岩心来获得重叠的时间序列，目的是构建一个长达100万年的连续时间序列。Juan de Fuca地区受益于以前的岩心，这些岩心显示出强大的年龄模型是可能的。该计划包括年龄模型和热液活动的沉积物地球化学，玻璃的主要和微量元素，放射性同位素分析，火山学评价，地幔熔融建模，以及定量统计和时间序列建模。 该方案有望开辟新的时间和方法学领域，可能对调查和了解洋脊产生深远影响。更广泛的影响包括培训多名研究生和博士后的最先进的技术，教育和参与哈佛大学本科生的邮轮，国际会议之间的相互作用冰川周期和固体地球过程，并在哈佛自然历史博物馆，收到250多个展览，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Ocean ridges are the sites of 80% of Earth’s volcanism. These features emit carbon dioxide and exert an important control on the chemical composition of the oceans through deep sea hot springs. The volcanoes are aligned along the 60,000 kilometer long ocean ridge system, where plates spread apart to create the sea floor. Studies of these volcanoes have been restricted to recent volcanic activity, because as the plates spread apart the volcanoes are covered by sediment and become inaccessible. For this reason, there is a present day snapshot of ocean ridge volcanism, but little possibility to study how it varies with one of the most important parameters of Earth science—time. Many aspects of geological phenomena cannot be understood without knowledge of their variations through time, called “time series”. For example, time series of climate show that that Earth passes into and out of ice ages, and that global warming is happening. New discoveries now permit the construction time series for ocean ridges by taking sediment cores along transects perpendicular to ocean ridges. The cores will be used to study volcanic glass that is preserved in the sediment. In particular, the time series will allow tests of the hypothesis that ice age cycles may influence cycles of ocean ridge volcanism and associated hydrothermal activity. Cruises to the Juan de Fuca ridge just off the coasts of Oregon and Washington will permit time series of one million years or more to be obtained for the first time. This project will provide support for undergraduate students to participate in the research cruise. In addition, the project will support an international conference and contribute to a museum exhibit at the Harvard Museum of Natural History.The European Research Council (ERC) has awarded a research grant for the scientific analyses to investigate time-series of ridge processes through a systematic coring program along transects perpendicular to the Juan de Fuca Ridge. The ERC grant to four principle investigators (three at GEOMAR in Germany and one at Harvard) did not include funding for collecting the sediment cores at sea. This proposal funds the ship time to obtain the necessary samples. A preliminary 11 day leg with the AUV SENTRY will obtain sediment thickness as well as high resolution bathymetry to guide the coring. Then, a 21 day leg will carry out 70 cores on three transects, two to the west of the ridge at different distances from the ridge transform intersection, and one to the east. The cruise would produce the first continuous, co-registered time series of glass compositions, hydrothermal activity and bathymetry over the 0 to 1Ma time scales. Time-series of basalt and sediment compositions at ocean ridges have been inaccessible because sea floor is rapidly covered by sediment and basalts are altered or have low potassium contents, making dating problematic. The 104-106 year time scale in particular is central for testing a host of hypotheses for mid-ocean ridges, from the existence and time scales of tectonic/magmatic cycles, to the continuity of magma chambers and hydrothermal systems, to possible relationships between glacial cycles and ridge processes since the Pleistocene. Preliminary data from cores near the ridge axis show that each core is likely to preserve 50-100ka time series of fresh glasses with interesting variations. Closely spaced cores will be used to obtain overlapping time series with the aim of constructing a long a continuous time series back to one million years. The Juan de Fuca region has the benefit of previous cores that show robust age models are possible. The program includes sediment geochemistry for age models and hydrothermal activity, major and trace elements of glasses, radiogenic isotope analyses, volcanological evaluation, modeling of mantle melting, and quantitative statistical and time-series modeling. This program holds the promise of opening new frontiers of time and methodology that may have far-reaching implications for the investigation and understanding of ocean ridges. Broader impacts include training multiple graduate students and post-docs in state of the art techniques, education and participation of Harvard undergraduates on the cruises, an international conference on interactions between glacial cycles and solid earth processes, and an exhibit at the Harvard Natural History Museum which receives more than 250,000 visitors per year including many K-12 students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.