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: 0425785
• 负责人: Charles Langmuir
• 金额: $ 19.85万
• 依托单位: Harvard 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 2007-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0425785&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.

知识分子的优点：Gakkel Ridge作为全球海洋山脊体系中最慢的最终成员提供了丰富的研究机会，其传播速度逐渐向东方降低。随着扩散率的降低，上层岩石圈的厚度增加。这种现象允许检查，并可能解决了与海壳形成有关的两个主要问题。首先，岩石圈厚度和地幔温度对海岭玄武岩起源的相对重要性是什么？如果海脊玄武岩记录地幔温度，它们将提供当前和过去地幔温度变化的宝贵记录。其次，海洋脊玄武岩同位素和痕量元件组成是否通过在熔化的小扩散量下的“脉壁套”组件的优先采样来控制？解决这个问题的解决方案对海洋火山的整个痕量元素和同位素记录具有影响。 2001年，北极中部山脊探险队（Amore）生产了来自200个以上车站的山脊和地下岩石的第一台高分辨率地图。 对主要元素，痕量元素和锶，肾近米和铅同位素的初步分析证明了意外发现的重要性 - 存在着在“稀疏的岩浆区域”沿着山脊的部分中发生的地幔域边界的存在，在山脊上，岩浆症下降到零件和巨人处于巨大的位置，并在巨大的位置散布在范围内。西方的样本与印度洋相似，而东方的样本类似于太平洋。尽管有这些复杂性，但在主要元素和痕量元素中，东部区域熔化量较低的预测信号仍然很明显。 可用的大型样品套件上的相干数据集将允许变量分开 - 地幔组成，扩散速率和地幔温度的相对作用。首席研究人员将进行一项重大的分析和建模计划：完成地球化学计划，以精确定义地幔域边界的位置和清晰度，以使用现有和新的主要元素数据和新的主要元素数据对熔融过程进行建模，以对两个域的跟踪元素和同位素的演变进行建模，并与其他海洋基础的详细相比，并比较其他海洋基础。新的数据和建模将可以清楚地比较岩石圈厚度的增加与在其他地方观察到的全球变化的影响之间。它们是否可以区分，并且这些差异是否与模型预测相符？重要的新方法将包括使用Hafnium同位素来评估石榴石在熔化过程中的重要性，以及对熔体夹杂物的激光消融ICP-MS分析，以了解融化和融化分离的过程以及它们如何在山脊上变化。新的地图和位置良好的样品还提供了测试岩浆分割模型的机会，以及明确定义和孤立的火山中心是地幔异质性，聚焦地幔流量或均匀流动的融化的结果。这项工作将继续与塔尔萨大学的彼得·迈克尔（Peter Michael）博士合作，他还将与俄勒冈州立大学的戴维·格雷厄姆（David Graham）博士进行分析，他正在衡量贵族气体，并与从该地区收回的橄榄岩样品的同事。 更广泛的含义：这项工作解决了与海壳和地幔有关的两个最重要的问题 - 地幔温度的分布以及地幔异质性的性质，这些问题在许多学科中具有广泛的重要性。它已经并且将继续是教育和推广的重要组成部分。学生参与了海上探险，这项工作将涉及两家机构的研究生和本科生的参与，并且将有一系列的公开演讲，以使更多的社区接触到新的美国破冰能力使历史性发现成为可能的历史发现。