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

洋脊是地球80%火山活动的发源地。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6万公里长的大洋山脊系统排列，在那里板块分开形成海底。对这些火山的研究仅限于最近的火山活动，因为随着板块的分散，火山被沉积物覆盖，变得无法进入。出于这个原因，现在有一张洋脊火山活动的快照，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。如果不知道地质现象随时间的变化，就无法理解地质现象的许多方面，这就是所谓的“时间序列”。例如，气候时间序列表明，地球进入和退出冰河时代，全球变暖正在发生。现在，新的发现允许沿垂直于洋脊的横断面采集沉积物岩心，从而建立洋脊的建造时间序列。这些岩心将被用来研究保存在沉积物中的火山玻璃。特别是，时间序列将允许对冰期周期可能影响洋脊火山活动和相关热液活动周期的假设进行测试。前往俄勒冈州和华盛顿州海岸附近的胡安德富卡海脊的邮轮将首次获得100万年或更长时间的时间序列。该项目将为本科生参与研究邮轮提供支持。此外，该项目将支持一个国际会议，并为哈佛大学自然历史博物馆的一个博物馆展览做出贡献。欧洲研究理事会(ERC)已经为科学分析提供了一项研究拨款，以通过沿胡安德富卡山脊垂直横断面的系统取芯计划来调查山脊过程的时间序列。环境研究中心向四名首席调查员(三名在德国GEOMAR，一名在哈佛)提供的赠款不包括在海上收集沉积物岩心的资金。这项提议为获得必要样品的船运时间提供了资金。与AUV哨所进行的初步11天航程将获得沉积物厚度以及指导取心的高分辨率水深测量。然后，21天的路段将在三个横断面上进行70个岩心，其中两个在山脊以西，距离山脊变换交叉口不同距离，一个在东面。这次巡航将在0至1 mA的时间尺度上产生第一个连续的、共同登记的玻璃成分、热液活动和水深测量的时间序列。洋脊玄武岩和沉积物成分的时间序列一直无法获取，因为海底很快被沉积物覆盖，玄武岩被改变或钾含量低，这使得测年成为问题。从构造/岩浆旋回的存在和时间尺度，到岩浆室和热液系统的连续性，再到更新世以来冰川旋回和海脊过程之间的可能关系，104-106年的时间尺度对于检验大洋中脊的一系列假说尤为重要。来自山脊轴线附近岩心的初步数据显示，每个岩心可能保存了50-100ka具有有趣变化的新鲜玻璃的时间序列。近距离的岩心将被用来获得重叠的时间序列，目的是构建一个长的、可追溯到100万年前的连续时间序列。胡安德富卡地区受益于以前的岩心，这表明建立稳健的年龄模型是可能的。该方案包括用于年龄模型和热液活动的沉积物地球化学、玻璃的主要元素和微量元素、放射性同位素分析、火山学评价、地幔熔融模型以及定量统计和时间序列模型。这一计划有望开辟新的时间和方法前沿，可能对洋脊的调查和理解产生深远影响。更广泛的影响包括对多名研究生和博士后进行最先进技术的培训，哈佛本科生在邮轮上的教育和参与，关于冰川周期和固体地球过程之间相互作用的国际会议，以及在哈佛自然历史博物馆举办的展览，该展览每年接待超过25万名参观者，其中包括许多K-12学生。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.