Accomplishment Based Renewal: The Architecture and Tectonics of the Ultraslow Spreading SW Indian and Gakkel Ridges

基于成就的更新：超慢速扩张的西南印度洋山脊和加克尔山脊的建筑和构造

• 批准号: 2114652
• 负责人: Richard Murray
• 金额: $ 99.68万
• 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: 2021
• 资助国家: 美国
• 起止时间: 2021-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2114652&HistoricalAwards=false
• 关键词: Accomplishment; Based; Renewal; Architecture; Tectonics

This project will photograph, describe, and curate a large collection of oceanic crustal rocks from two ultraslow spreading ridges – the Gakkel Ridge (GR) in the Arctic Ocean and the Southwest Indian Ridge (SWIR) in the oceans that surround southern Africa. These ridges represent two distinctly different ultraslow spreading centers with the SWIR having a large number of fracture zones and hot spot activity while the GR has no transform faults and no evidence of hotspots. The rock collection will be integrated with previously collected geophysical data (magnetics, gravity, multibeam maps and seismic data) and newly acquired electron microprobe data from a subset of representative samples to estimate chemical compositions of the crust and mantle rocks. Together these will be used to estimate the thickness and architecture of the ocean crust and assess the amount of interaction they have with seawater and the underlying mantle. This work provides future researchers with on-line access to the entire collection of slow-spreading crustal rocks collected over the past 50 years. This project is a three year research program with several important goals. First, it will provide a photo-archive of thousands of seafloor crustal samples previously collected and housed at Woods Hole Oceanographic Institute. As part of this archival, it will allow researchers to synthesize descriptive data with archives of geophysical, magnetic, and geochemical data available in this region. New chemical compositional data will be added through electron microprobe analysis on a subset of representative crustal rocks from two ultraslow spreading ridges – the SW Indian Ridge (SWIR) and the Gakkel Ridge. This study will also integrate petrological and geochemical data with the extensive collection of multibeam maps of the SWIR and existing seismic, magnetics, and gravity data, and the uniquely comprehensive rock sampling performed along the ridge axis and rift mountains. The goal is to test the hypothesis that spreading centers along the Ridge are not supported by deep mantle plumes, but by the depleted residues of hydrous mantle melting beneath ancient island arcs and back arc basins related to the closure of the Mozambique Ocean in the Neoproterozoic. It further attempts to determine the origin of the associated hotspots, and how they are interacting with the SWIR as evidenced by the geochemistry and petrology of the modern ridge, and the off-axis bathymetry and magnetics across the seafloor to the hotspots and their conjugate positions. In addition, a parallel synthesis of the ultraslow spreading Gakkel Ridge will be completed providing the first detailed analysis of the geology of the ridge based on the 190 successful dredge and rock core stations along the 1,000 km stretch mapped along it during the AMORE Expedition. At present analysis of the AMORE data, including the bathymetry, has been largely limited to the isotopic, major and trace element geochemistry of the lavas, and peridotites. This ridge is a near perfect contrast to the Ultraslow SWIR. The Gakkel Ridge has no transform faults (the SWIR has many) thus providing a unique opportunity to examine the causes and extent of geochemical variability and magmatic segmentation in their absence, and what features are due to ultraslow spreading and which to transforms. Finally, the funding will allow the researcher to finish a detailed manuscript comparing the dike-gabbro transitions at fast, slow and ultraslow-spreading ridges, providing direct evidence for a shallow melt lens at the dike-gabbro transition at the former, and its general absence at the latter.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.

该项目将拍摄、描述和整理来自两个超慢扩张脊的大量海洋地壳岩石——北冰洋的加克尔海脊（GR）和环绕非洲南部的海洋中的西南印度海脊（SWIR）。两个截然不同的超慢速扩张中心，其中 SWIR 具有大量断裂带和热点活动，而 GR 没有转换断层，也没有热点证据。岩石收集将与之前收集的地球物理数据相结合。 （磁力、重力、多波束图和地震数据）以及从代表性样本子集中新获取的电子探针数据，以估计地壳和地幔岩石的化学成分，这些数据将一起用于估计海洋地壳和地幔的厚度和结构。评估它们与海水和底层地幔的相互作用程度。这项工作为未来的研究人员提供了在线获取过去 50 年来收集的所有缓慢扩张的地壳岩石的信息。一些首先，它将提供先前在伍兹霍尔海洋研究所收集和保存的数千个海底地壳样本的照片档案，作为该档案的一部分，它将允许研究人员将描述性数据与地球物理、磁力和地质学档案进行综合。本研究将通过对两个超慢扩张脊（SWIR）和加克尔海脊（Gakkel Ridge）的代表性地壳岩石子集进行电子探针分析，添加该地区现有的地球化学数据。还将岩石学和地球化学数据与广泛收集的短波红外多波束图以及现有的地震、磁学和重力数据以及沿山脊轴和裂谷山进行的独特的综合岩石采样相结合，目标是检验扩散的假设。洋脊沿线的中心并非由深部地幔柱支撑，而是由与莫桑比克洋闭合有关的古代岛弧和弧后盆地下方熔化的含水地幔的耗尽残留物支撑。它进一步尝试确定相关热点的起源，以及它们如何与现代海脊的地球化学和岩石学以及从海底到热点及其它们的离轴测深和磁学所证明的相互作用。此外，超慢速扩张的 Gakkel 山脊的并行合成也将完成，基于 190 个成功的山脊地质情况进行首次详细分析。 AMORE 探险期间沿线绘制的 1,000 公里范围内的挖泥站和岩心站 目前，对 AMORE 数据（包括测深）的分析主要限于熔岩和橄榄岩的同位素、主量和微量元素地球化学。该山脊与超慢短波红外形成了近乎完美的对比，加克尔山脊没有转换断层（短波红外有很多），因此提供了一个独特的机会来检查转换断层的原因和程度。最后，这笔资金将使研究人员能够完成一份详细的手稿，比较快速、慢速和超慢速扩张山脊的岩脉-辉长岩转变。 ，为前者的岩脉-辉长岩过渡处存在浅熔体透镜体以及后者普遍不存在提供了直接证据。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准。