Collaborative Research: Petrology and Geochemistry of Gakkel Ridge Basalts

合作研究：Gakkel 岭玄武岩的岩石学和地球化学

• 批准号: 0425686
• 负责人: Steven Goldstein
• 金额: --
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-08-15 至 2008-02-29
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0425686&HistoricalAwards=false
• 关键词: Collaborative; Research; Petrology; Geochemistry; Gakkel

Intellectual Merits: The Gakkel Ridge provides rich research opportunities as the slowest spreading end member of the global system of ocean ridges, with the spreading rate decreasing progressively towards the east. As the spreading rate decreases, the thickness of the overlying lithosphere increases. This phenomenon permits examination and possibly resolution of two major questions pertinent to the formation of the ocean crust. First, is what the relative importance of lithospheric thickness and mantle temperature on the genesis of ocean ridge basalts? If ocean ridge basalts record mantle temperature, they will provide a valuable record of current and past mantle temperature variations. Second, are ocean ridge basalt isotope and trace element compositions controlled by preferential sampling of a "veined mantle" component at small extents of melting? Resolution of this question has implications for interpretations of the entire trace element and isotope record of oceanic volcanics. The Arctic Mid-Ocean Ridge Expedition (AMORE) in 2001 produced the first high resolution map of the ridge and basement rocks from over 200 stations. Preliminary analyses for major elements, trace elements, and strontium, neodymium, and lead isotopes demonstrate the importance of an unexpected discovery-the existence of a mantle domain boundary that occurs in a "sparsely magmatic zone" part way along the ridge, where magmatism drops to zero and peridotites are emplaced at the spreading axis. Samples to the west are similar to the Indian Ocean, while those to the east are similar to the Pacific. Despite these complexities, the predicted signal of low extents of melting in the eastern region is clear in both major and trace elements. Coherent data sets on the large suite of samples available will permit a separation of variables-the relative roles of mantle composition, spreading rate, and mantle temperature. The Principal Investigators will undertake a major analytical and modeling program: to complete the geochemical program to precisely define the location and sharpness of the mantle domain boundary, to model the melting process using existing and new major and trace element data, to model the trace element and isotope evolution of both domains, and to make detailed comparisons of the Arctic Basin signal to other ocean basins. The new data and modeling will permit a clear comparison between the effects of increasing lithospheric thickness and the global variations observed elsewhere. Are they distinguishable, and do these differences accord with model predictions? Important new approaches will include using hafnium isotopes to evaluate the importance of garnet in the melting process, and laser ablation ICP-MS analysis of melt inclusions to gain insights into processes of melting and melt segregation and how they vary along the ridge. The new maps and well located samples also give the opportunity to test models of magmatic segmentation, and whether clearly defined and isolated volcanic centers are the result of mantle heterogeneity, focusing of mantle flow, or melt focusing of uniform flow. This work will continue the collaboration with Dr. Peter Michael, University of Tulsa, who will also do analytical work on volatile elements, with Dr. David Graham, Oregon State University, who is measuring noble gasses, and with colleagues working on the peridotite samples recovered from this region. Broader Implications: This work addresses two of the most significant issues pertinent to the ocean crust and mantle-the distribution of mantle temperature and the nature of mantle heterogeneity, which have broad importance across many disciplines. It has had, and will continue, to have an important component of education and outreach. Students were involved in the sea-going expedition, the work will involve participation by both graduate and undergraduate students at two institutions, and there will be a series of public lectures to expose more of the community to the historic discoveries made possible by the new U. S. ice-breaking capability.

智力优势：加克尔海岭作为全球洋脊系统中扩张速度最慢的端部成员，向东扩张速度逐渐降低，提供了丰富的研究机会。当扩张速率降低时，上覆岩石圈的厚度增加。这一现象使人们得以研究并可能解决与洋壳形成有关的两个主要问题。第一，岩石圈厚度和地幔温度对洋中脊玄武岩成因的相对重要性是什么？如果洋中脊玄武岩记录了地幔温度，它们将为现在和过去的地幔温度变化提供有价值的记录。第二，洋中脊玄武岩的同位素和微量元素组成是否受“脉状地幔”成分在小范围熔融时的优先取样控制？这个问题的解决对解释大洋火山岩的整个微量元素和同位素记录具有重要意义。 2001年的北极大洋中脊考察（AMORE）制作了第一张高分辨率的海脊和基底岩石图，来自200多个观测站。 对主元素、微量元素和锶、钕、铅同位素的初步分析证明了一个意外发现的重要性--地幔域边界的存在，它发生在沿着洋脊的“稀疏岩浆区”，在那里岩浆活动降至零，橄榄岩侵位在扩张轴上。西部的样品与印度洋相似，而东部的样品与太平洋相似。尽管存在这些复杂性，但东部地区融化程度低的预测信号在主要和微量元素方面都是明确的。 现有大量样品的相干数据集将允许分离变量地幔成分、扩展速率和地幔温度的相对作用。主要研究人员将进行一项主要的分析和建模计划：完成地球化学计划，以精确定义地幔域边界的位置和锐度，使用现有和新的主要和微量元素数据模拟熔融过程，模拟两个域的微量元素和同位素演变，并将北极盆地信号与其他海洋盆地进行详细比较。新的数据和模型将允许在岩石圈厚度增加的影响与其他地方观察到的全球变化之间进行清晰的比较。它们是可区分的吗？这些差异是否与模型预测雅阁？重要的新方法将包括使用铪同位素来评估石榴石在熔化过程中的重要性，以及对熔体夹杂物进行激光烧蚀ICP-MS分析，以深入了解熔化和熔体偏析的过程以及它们如何沿沿着脊变化。新的地图和定位良好的样品也提供了机会，以测试岩浆分割模型，以及是否明确界定和孤立的火山中心是地幔不均匀性的结果，地幔流的聚焦，或熔体集中的均匀流动。这项工作将继续与塔尔萨大学的Peter Michael博士合作，他也将对挥发性元素进行分析工作，与俄勒冈州州立大学的大卫格雷厄姆博士合作，他正在测量惰性气体，并与同事合作研究从该地区回收的橄榄岩样品。 更广泛的影响：这项工作解决了与洋壳和地幔相关的两个最重要的问题--地幔温度的分布和地幔不均匀性的本质，这在许多学科中具有广泛的重要性。它已经并将继续具有教育和外联的重要组成部分。学生们参与了这次航海探险，这项工作将涉及两个机构的研究生和本科生的参与，并将有一系列的公开讲座，以使更多的社区接触到新的美国科学家的历史发现。S.破冰能力。