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

地球上80%的火山活动都发生在洋脊上。这些特征释放二氧化碳，并通过深海温泉对海洋的化学成分施加重要控制。火山沿着6万公里长的洋脊系统排列，在那里板块分开形成了海底。对这些火山的研究仅限于最近的火山活动，因为随着板块分开，火山被沉积物覆盖，变得难以接近。由于这个原因，现在有一个海洋山脊火山活动的快照，但几乎没有可能研究它如何随着地球科学中最重要的参数之一——时间的变化而变化。地质现象的许多方面，如果不知道它们随时间的变化，就无法理解，这种变化被称为“时间序列”。例如，气候的时间序列表明，地球进入和走出冰河时代，全球变暖正在发生。新的发现现在允许沿垂直于洋脊的横断面提取沉积物岩心来构建洋脊的时间序列。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，时间序列将允许检验冰期周期可能影响洋脊火山活动周期和相关热液活动周期的假设。乘船前往俄勒冈州和华盛顿州海岸附近的胡安·德·富卡山脊，将首次获得100万年或更长时间的时间序列。本项目将为本科生参加研游提供支持。此外，该项目将支持一个国际会议，并为哈佛自然历史博物馆的博物馆展览做出贡献。欧洲研究委员会（ERC）已经为科学分析提供了一笔研究经费，通过一个系统的取心程序，沿着垂直于胡安德富卡山脊的横断面调查山脊过程的时间序列。ERC给四位主要研究者（三位在德国GEOMAR，一位在哈佛）的拨款不包括在海上收集沉积物岩心的资金。该提案为获取必要样品的装船时间提供资金。在为期11天的初步测试中，AUV SENTRY将获得沉积物厚度和高分辨率测深数据，以指导取心。然后，一个为期21天的项目将在三个横断面上进行70个核心，两个在山脊的西部，距离山脊变换交叉点不同的距离，一个在东部。这次巡航将产生第一个连续的、共同记录的时间序列，包括玻璃成分、热液活动和深度测量，时间跨度为0到1Ma。由于海底被沉积物迅速覆盖，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组成的时间序列，这使得测年变得困难。104-106年的时间尺度对于检验一系列关于洋中脊的假设尤其重要，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与洋中脊过程之间的可能关系。脊轴附近岩心的初步数据显示，每个岩心可能保存了50-100ka时间序列的新鲜玻璃，具有有趣的变化。将使用紧密间隔的岩心来获得重叠时间序列，目的是构建一个长达一百万年的连续时间序列。Juan de Fuca地区得益于以前的岩心，这些岩心表明，可靠的年龄模型是可能的。该项目包括用于年龄模型和热液活动的沉积物地球化学，玻璃的主要和微量元素，放射性同位素分析，火山学评估，地幔融化建模，以及定量统计和时间序列建模。该计划有望开辟时间和方法的新领域，这可能对海洋脊的调查和理解产生深远的影响。更广泛的影响包括培养多名研究生和博士后掌握最先进的技术，教育和参与哈佛本科生的游轮，关于冰川循环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，每年接待超过25万名游客，其中包括许多K-12学生。该奖项反映了美国国家科学基金会的法定使命，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.