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

该项目将拍摄，描述和策划来自两个超低速扩张脊的大量海洋地壳岩石-北冰洋的Gakkel Ridge（GR）和南部非洲周围海洋的西南印度洋海岭（SWIR）。 这些脊代表了两个明显不同的超低速扩张中心，SWIR具有大量的断裂带和热点活动，而GR没有转换断层，也没有热点的证据。 岩石集将与之前收集的地球物理数据（磁力、重力、多束地图和地震数据）以及从代表性样本子集中新获取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底层地幔的相互作用量。 这项工作为未来的研究人员提供了在线访问过去50年来收集的缓慢扩展的地壳岩石的整个集合。该项目是一个为期三年的研究计划，有几个重要目标。 首先，它将提供以前收集并存放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，它将使研究人员能够将描述性数据与该地区现有的地球物理，磁性和地球化学数据档案相结合。 新的化学成分数据将通过电子探针分析的一个子集的代表性地壳岩石从两个超低速扩张脊-西南印度洋脊（SWIR）和Gakkel脊。 这项研究还将整合岩石学和地球化学数据，广泛收集SWIR的多波束图和现有的地震、磁力和重力数据，以及沿着山脊轴和裂谷山脉进行的独特的综合岩石取样。我们的目标是测试这一假设，即扩张中心沿着的脊不支持深地幔柱，但由耗尽残留物的含水地幔熔融下古老的岛弧和弧后盆地有关的莫桑比克海洋在新元古代关闭。它还试图确定相关热点的起源，以及它们如何与SWIR相互作用，如现代海脊的地球化学和岩石学所证明的那样，以及从海底到热点及其共轭位置的离轴测深和磁力。此外，还将完成对超低速扩展的加克尔海脊的平行综合，根据AMORE考察期间沿沿着1 000公里的地形绘制的190个沿沿着成功的挖掘和岩芯站，对海脊的地质进行首次详细分析。目前，对AMORE数据的分析，包括水深测量，主要限于熔岩和橄榄岩的同位素、主要和微量元素地球化学。这个脊与超低短波红外线形成了近乎完美的对比。Gakkel岭没有转换断层（SWIR有很多），因此提供了一个独特的机会来研究地球化学变化和岩浆分段的原因和程度，以及什么特征是由于超低速扩张和转换。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岩脉-辉长岩过渡，为前者岩脉-辉长岩过渡处的浅熔融透镜提供直接证据，该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的评估来支持。影响审查标准。

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.