Collaborative Research: Developing New Models of Oceanic Magmatism and Source Heterogeneity Using the 8 degree 20' N Seamounts as Windows into the Sub-Ridge Mantle

合作研究：利用北纬 8 度 20 英尺海山作为进入亚脊地幔的窗口，开发大洋岩浆作用和源异质性的新模型

• 批准号: 2001331
• 负责人: Virginia Dorsey Wanless
• 金额: $ 16.21万
• 依托单位: Boise State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2020
• 资助国家: 美国
• 起止时间: 2020-05-01 至 2025-04-30
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2001331&HistoricalAwards=false
• 关键词: Collaborative; Research; Developing; New; Models

Eruptions of lava form submarine volcanoes, known as seamounts, near mid-ocean ridge spreading centers. These lavas can provide important information about what Earth’s uppermost (~ 120 miles) mantle is composed of and how it melts to form the majority of Earth’s crust. At present no studies have examined long chains of seamounts adjacent to mid-ocean ridges to address these fundamental questions. In this study, we plan to analyze over 400 well located lava samples from the 8°20'N seamount chain. The chain was previously sampled and mapped in 2016 and 2018 using the submersible Alvin and autonomous vehicle Sentry. The geochemical, mineralogical, and age data to be obtained under this project will allow us to determine the origin of the magmas that feed the seamounts and nearby ridge. The data will also tell us how those magmas evolve to form oceanic lavas, and how the volcanism is related to regional tectonic processes. The study will promote advances in the field of geochemistry, marine geology, and geodynamics. This project will provide significant mentorship and training for students at a variety of levels. It will fully or partially support three graduate students at Florida and Boise State and will provide training for several undergraduates in geochemical techniques and interpretation, and support senior research projects. The project will also support education and diversity by funding two female scientists, one a first-generation college graduate, toward obtaining their PhDs in geochemistry. Both principal investigators are heavily involved in outreach and education at the K-12 levels in Florida and Idaho.Sparse sampling and geochemical analyses of seamounts scattered throughout the northeastern Pacific suggest the sub-ridge mantle associated with the East Pacific Rise (EPR) has far greater compositional variability then is preserved in lavas erupted on-axis. While the relative homogeneity of axial lavas has resulted in intriguing generalizations about magma differentiation and mixing processes at mid-ocean ridges (MOR), seamount studies have had a significant impact on our understanding of the source compositions for oceanic basalts, the scales of mantle heterogeneity, and mantle melting systematics at MOR. However, many of these studies have focused on dredged lavas from individual seamounts with very few combining in situ sampling and high-resolution mapping from a single chain oriented perpendicular to the ridge axis. To fill this gap in knowledge about the sub-ridge mantle, two research cruises in 2016 and 2018 investigated the 8°20’N seamount chain that extends ~200km west of the EPR. The 8°20’N seamount chain was unexplored and virtually unsampled before our highly successful OASIS cruises. Geophysical, observational, and preliminary geochemical data from this nearly continuous chain of volcanoes led us to unexpected discoveries about their construction and revealed extreme compositional variability in the near MOR mantle that was previously only surmised from regional seamount studies in the northeast Pacific. The location, orientation, and preliminary data from the 8°20'N seamount chain make it an ideal a natural laboratory to investigate source heterogeneity and melting systematics in the near-ridge mantle. We propose to study the petrologic processes and mantle sources feeding MOR and near-axis volcanoes though comprehensive geochemical analyses of lavas and melt inclusions from the 8°20’N seamounts. Site-specific sampling using HOV Alvin and extensive, fine-scale mapping with AUV Sentry along the seamount chain, coupled with our previous comprehensive investigations of the 8°- 10°N EPR provide an exceptional opportunity to constrain geodynamic and geochemical models of mantle melting near MOR and determine the extent and length scales of mantle heterogeneity. We propose to collect a wide spectrum of petrologic and geochemical data including Sr, Nd, Pb, and Os isotopes, melt inclusion compositions, volatile contents, and 40Ar/39Ar age dates of lavas from the extensive collection of samples we have from the 8°20’N seamount chain. These results will be combined with numerical models to produce a petrologic model of mantle melting and magmatic processes in the near-ridge mantle. This extensive off-axis seamount chain provides a rare opportunity to probe the compositions of the mantle near MOR and to understand how magmas are spatially and temporally distributed in the shallow mantle and crust. Results from this research have implications for the generation of the majority of Earth’s crust.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.

熔岩的喷发形成海底火山，称为海山，位于大洋中脊扩展中心附近。这些熔岩可以提供有关地球最上层（约 120 英里）地幔的组成以及它如何融化形成大部分地壳的重要信息。目前还没有研究检查邻近大洋中脊的长海山链来解决这些基本问题。在这项研究中，我们计划分析来自大洋中脊的 400 多个位置良好的熔岩样本。北纬 8°20' 的海山链此前已于 2016 年和 2018 年使用潜水器 Alvin 和自动驾驶车辆 Sentry 进行了采样和测绘。根据该项目获得的地球化学、矿物学和年龄数据将使我们能够确定海山链的起源。这些数据还将告诉我们这些岩浆如何演化形成海洋熔岩，以及火山活动与区域构造的关系。该研究将促进地球化学、海洋地质学和地球动力学领域的进步，该项目将为各个级别的学生提供重要的指导和培训，并将全部或部分支持佛罗里达州和博伊西州立大学的三名研究生。该项目将为几名本科生提供地球化学技术和解释方面的培训，并支持高级研究项目，还将资助两名女科学家（其中一名是第一代大学毕业生）获得地球化学博士学位。积极参与佛罗里达州和爱达荷州 K-12 年级的外展和教育。对分布在整个东北太平洋的海山进行的稀疏采样和地球化学分析表明，与东太平洋隆起 (EPR) 相关的下脊地幔的成分变异性比在东太平洋隆起 (EPR) 中保存的要大得多。虽然轴向熔岩的均匀性导致了对大洋中脊（MOR）岩浆分化和混合过程的有趣概括，但海山研究相对对我们产生了重大影响。然而，许多这些研究都集中在单个海山的疏浚熔岩上，很少将现场采样和高分辨率绘图结合起来。垂直于山脊轴的单链为了填补有关山脊地幔的这一知识空白，2016 年和 2018 年的两次研究巡航对该区域进行了调查。北纬 8°20' 海山链，在 EPR 以西延伸约 200 公里。 在我们从这条几乎连续的链中获得非常成功的地球物理、观测和初步地球化学数据之前，北纬 8°20' 海山链尚未勘探过，也几乎没有进行采样。火山使我们对它们的构造有了意想不到的发现，并揭示了 MOR 地幔附近的极端成分变化，而这一点以前只能通过东北太平洋的区域海山研究推测出来。方向和来自 8°20'N 海山链的初步数据使其成为研究近脊地幔源异质性和熔融系统的理想天然实验室。我们建议研究供给 MOR 和近地幔的岩石学过程和地幔源。通过使用 HOV Alvin 对 8°20'N 海山的熔岩和熔体包裹体进行全面的地球化学分析，并使用 AUV Sentry 沿海山链进行广泛、精细的绘图，对轴火山进行了分析。通过我们之前对 8°- 10°N EPR 的全面调查，我们提供了一个绝佳的机会来约束 MOR 附近地幔熔化的地球动力学和地球化学模型，并确定地幔非均质性的范围和长度尺度。地球化学数据包括 Sr、Nd、Pb 和 Os 同位素、熔体包裹体成分、挥发物含量和熔岩的 40Ar/39Ar 年龄日期，这些数据来自我们从8°20'N 海山链。这些结果将与数值模型相结合，生成近脊地幔中地幔熔化和岩浆过程的岩石学模型。这条广泛的离轴海山链为探测地幔成分提供了难得的机会。 MOR 附近的地幔，并了解岩浆如何在浅地幔和地壳中在空间和时间上分布。这项研究的结果对大部分地壳的形成具有重要意义。该奖项反映了 NSF 的法定使命，并得到了美国国家科学基金会 (NSF) 的认可。通过使用基金会的智力优点和更广泛的影响审查标准进行评估，认为值得支持。