Collaborative Research: Thin Crust Over the Marion Rise: Remelting the Gondwanan Mantle

合作研究：马里恩海隆上的薄地壳：冈瓦纳地幔的重熔

• 批准号: 1657983
• 负责人: Masako Tominaga
• 金额: $ 63.98万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-10-01 至 2024-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1657983&HistoricalAwards=false
• 关键词: Collaborative; Research; Thin; Crust; Over

It has long been assumed that the Earth consists of a thin, outer, silica-rich, hardened crust overlying a thick layer of silica-poor, magnesium-rich, mantle rock known as peridotite and an inner, nickel-iron core. Compared to Earth's ~40 kilometer thick continental crust, ocean crust is generally considered to be relatively thin (i.e., 6-7 km thick). One of the most exciting discoveries in ocean sciences over the last 15 years has been the discovery that parts of the seafloor do not have normal ocean crust, but rather Earth's mantle is exposed directly on the seafloor over large regions of the Arctic, Indian, and Atlantic Oceans. Just how much of the seafloor is exposed mantle not presently known, although estimates have been made that predict up to 25%. This research comprises the US portion of a two-ship, US-German, collaborative project designed to map, collect gravity and magnetic geophysical data, and sample a large areas of the seafloor along the Southwest Indian Ridge in the western Indian Ocean to determine how much mantle rock is exposed there. Geophysical data and geochemical analysis of major and trace elements and various isotopes will be carried out post-cruise at shore-based laboratories. The results of this work, combined with ongoing French studies on the eastern portion of the southwest Indian Ridge will allow, for the first time, an accurate estimate of how much mantle is exposed along an entire mid-ocean ridge. More than 80% of this region has never been mapped and sampling has been largely restricted to a few sections of a narrow 3-mile-wide rift valley that forms the southwest Indian Ridge mid-ocean ridge spreading center. This work is important because mantle rock is very unstable at the Earth's surface, particularly on the seafloor where it is exposed to and extensively reacts with seawater. These reactions produce hydrogen and methane, which, in turn, provide energy for bacterial life in the deep sea and support what could be an extensive biomass below the seafloor that is presently not accounted for in the inventory of life supported by our planet. The reactions between seawater and mantle rock also potentially sequester carbon in the form of carbonate minerals that form by the removal of CO2 from seawater, thereby affecting global and atmospheric carbon budgets at different time scales. Broader impacts of the work include training of graduate students at three institutions, support of an early career scientist from a gender under-represented in the sciences, outreach to elementary and high schools, and public outreach. This project takes to sea a high school teacher and a scientific blogger, who will conduct live interaction sessions with students during the oceanographic expedition and who will prepare age-appropriate educational materials and radio documentaries of the research and oceanographic cruise. There is also a significant component of international collaboration with German, Italian, and Chinese scientists some of whom will participate in the expedition and interact closely with the students and US faculty, further building international relations with these scientific communities.This research consists of an oceanographic expedition to the crest of the Marion Rise on the Southwest Indian Ridge to test the hypothesis that that the Marion Rise is supported by lateral mantle heterogeneity produced by the recycling different Gondwanan mantle provinces beneath the modern ocean ridge, as opposed to a thermal anomaly due to a mantle plume. This is the first leg of a two-leg US-German-Chinese international program to study the Marion platform, a little studied part of the seafloor, and its origin. The cruise will use multibeam sonar to map the seafloor in the area, will dredge rocks for later shore-based laboratory analysis, collect gravity and magnetic geophysical data, and carry out geochemical analyses of select samples. Sea surface magnetics will be used to locate central magnetic anomalies to identify spreading centers and determine spreading rate asymmetries. Regions of a amagmatic seafloor spreading will be determined by their weak magnetic signal and lack of easily definable magnetic lineations. Gravity surveys will allow calculation of residual mantle Bouguer anomalies from which magmatically robust regions can be identified on the basis of their characteristic negative lows. In addition to on-axis work, the expedition will include extensive off-axis dredging to help delineate mantle domains and major magmatic centers. Post-cruise research includes petrographic and geochemical analysis of collected seafloor basalts and peridotites to determine the nature and origin of the mantle source in the Marion Rise area. Chinese collaborators will conduct major and trace element analyses of dredged rocks and US laboratories will analyze the isotopes and isotopic ratios of Hf, and Os as well as radiogenic isotopes of Sr, Nd, and Pb. Calculation of the mantle using geochemically determined mantle density gradients will estimate the extent of serpentinization in the exposed mantle sections. This, together with processed magnetization data, lithologic analysis of collected rock samples, and multi-channel sonar bathymetry will be used to construct a geologic map of the area to determine the tectonic evolution and crustal architecture of the Platform. This work fills a significant sampling gap on mid-ocean ridges and will enhance significantly our understanding of global mantle variability as well as provide new insights into the nature of shallow mantle convection and on the origin of mantle hotspots.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.

长期以来，人们一直认为地球是由薄的，外部，富含二氧化硅的硬皮组成的，上面覆盖了一层厚的二氧化硅，富含镁的岩石，地幔岩石，被称为橄榄岩和内部的镍铁核。 与地球约40公里厚的大陆壳相比，海壳通常被认为是相对较薄的（即6-7 km厚）。在过去15年中，海洋科学中最令人兴奋的发现之一是发现，海底的部分地区没有正常的海壳，而是地球的地幔直接在北极，印度和大西洋的大型地区的海底暴露在海底上。尽管已经预测到高达25％的估计，但目前尚不清楚多少海底的海底。这项研究包括一个两架美国 - 德国，合作项目的美国部分，旨在绘制，收集重力和磁地球物理数据，并在印度洋西部的西南印度山脊沿着海底的大片海底进行采样，以确定那里暴露了多少地幔岩。主要和微量元素以及各种同位素的地球物理数据和地球化学分析将在基于岸的实验室进行裁缝进行。这项工作的结果以及对西南印度山脊东部地区的法国研究的持续研究将首次允许对整个海山山脊沿着整个中山山脊暴露的地幔进行准确的估计。该地区的80％以上从未被绘制过，并在很大程度上仅限于狭窄的3英里宽裂谷谷的几个部分，该部分构成了西南印度山脊中山脉中山山脊传播中心。这项工作很重要，因为地幔岩石在地面的表面非常不稳定，尤其是在海底暴露于海水并与海水反应广泛的海底上。这些反应会产生氢和甲烷，从而为深海中的细菌寿命提供了能量，并支持在海底下方的广泛生物量，目前在我们地球支持的生命库存中尚未考虑。 海水和地幔岩之间的反应也有可能以碳酸盐矿物质形式隔离碳，这些碳矿物质是通过从海水中去除二氧化碳而形成的，从而影响了不同时间尺度的全球和大气碳预算。这项工作的更广泛的影响包括在三个机构的研究生中培训研究生，这是从科学领域的性别不足的早期职业科学家的支持，对小学和高中的宣传以及公共宣传。该项目将成为一名高中老师和科学博客作者，他们将在海洋探险期间与学生进行实时互动，并准备适合年龄的教育材料以及研究和海洋巡游的广播纪录片。国际与德国，意大利语和中国科学家的国际合作也有很大的组成部分不同的冈瓦南地幔省在现代海洋山脊下方，而不是由于地幔羽流而导致的热异常。这是研究Marion平台，一部研究的一部分海底及其起源的两腿美国 - 中国国际计划的第一站。该巡航将使用多束声纳来绘制该地区的海底，将挖出岩石，以进行以后的基于海岸的实验室分析，收集重力和磁地球物理数据，并对精选样品进行地球化学分析。海面磁化剂将用于定位中央磁异常，以识别扩散中心并确定扩散速率不对称。陷入困境的海底扩散区域将取决于它们的弱磁信号和缺乏易于定义的磁线。重力调查将允许计算残留的地幔布格异常情况，可以根据其特征性负低点识别岩浆稳健区域。除轴上的工作外，该探险还将包括大量的离轴疏g，以帮助划定地幔域和主要岩浆中心。灌溉后的研究包括对收集的海底玄武岩和橄榄岩的岩石学和地球化学分析，以确定马里恩崛起区域中地幔源的性质和起源。中国合作者将对疏岩石进行重大和痕量元素分析，美国实验室将分析HF的同位素和同位素比，以及OS以及SR，ND和PB的放射异位素。使用地球化地幔密度梯度计算地幔的计算将估计暴露的地幔切片中蛇形化的程度。这与加工后的磁化数据，收集的岩石样品的岩性分析以及多通道声纳测深度法将用于构建该区域的地质图，以确定平台的构造演化和地壳结构。这项工作填补了中端脊的显着抽样差距，将大大增强我们对全球地幔变异性的理解，并提供有关浅层对流性质以及地幔热点本质的新见解。该奖项奖反映了NSF的法定任务，并通过使用基金会的智力效果和广泛的影响来评估NSF的法定任务。

项目成果

Plate-Driven Micro-Hotspots and the Evolution of the Dragon Flag Melting Anomaly, Southwest Indian Ridge

板块驱动的微热点和西南印度洋中脊龙旗融化异常的演化

• DOI: 10.1016/j.epsl.2019.116002
• 发表时间: 2020
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Yu Xing;Dick H.J.B.
• 通讯作者: Dick H.J.B.