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

该项目将拍摄、描述和整理来自两个超低扩展脊的大量海洋地壳岩石——北冰洋的Gakkel脊（GR）和南部非洲周围海洋的西南印度洋脊（SWIR）。这些隆起代表了两个明显不同的超低扩张中心，其中SWIR有大量的断裂带和热点活动，而GR没有转换断层和热点证据。岩石收集将与以前收集的地球物理数据（磁学、重力、多波束图和地震数据）以及从代表性样品子集中新获得的电子显微探针数据相结合，以估计地壳和地幔岩石的化学成分。这些数据将被用来估计海洋地壳的厚度和结构，并评估它们与海水和下面的地幔相互作用的程度。这项工作为未来的研究人员提供了在线访问过去50年来收集的所有缓慢扩散的地壳岩石的机会。这个项目是一个为期三年的研究项目，有几个重要的目标。首先，它将提供以前收集并保存在伍兹霍尔海洋研究所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该地区可用的地球物理、磁和地球化学数据档案综合起来。通过对西南印度脊（SWIR）和Gakkel脊这两个超低扩展脊的代表性地壳岩石进行电子探针分析，将增加新的化学成分数据。该研究还将整合岩石学和地球化学数据、广泛收集的SWIR多波束图和现有的地震、磁力和重力数据，以及沿山脊轴和裂谷山脉进行的独特的综合岩石采样。其目的是验证这样一种假设，即沿洋脊扩散的中心不是由深层地幔柱支撑的，而是由新元古代莫桑比克海洋封闭时期的古岛弧和弧后盆地下含水地幔融化的耗尽残留物支撑的。它进一步试图确定相关热点的起源，以及它们如何与SWIR相互作用，这可以通过现代脊的地球化学和岩石学，以及海底到热点及其共轭位置的离轴测深和磁学来证明。此外，将完成超低扩展Gakkel Ridge的平行合成，根据AMORE远征期间沿其绘制的1000公里长的190个成功的清浚和岩石岩心站，提供对山脊地质的第一次详细分析。目前对AMORE数据的分析，包括测深，主要局限于熔岩和橄榄岩的同位素、主要元素和微量元素的地球化学分析。这个山脊与超低SWIR形成了近乎完美的对比。Gakkel Ridge没有转换断层（SWIR有很多），因此提供了一个独特的机会，可以在没有转换断层的情况下研究地球化学变异和岩浆分割的原因和程度，以及哪些特征是由超低扩展引起的，哪些是由转换引起的。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、缓慢和超低扩展脊的脉岩-辉长岩转变，为前者脉岩-辉长岩转变处存在浅层熔融透镜体，而后者脉岩-辉长岩转变处普遍不存在熔融透镜体提供直接证据。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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.