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

该项目将拍摄、描述和管理来自两个超低扩张海脊的大量大洋地壳岩石--北冰洋的Gakkel海脊(GR)和南部非洲周围海洋的西南印度洋海脊(SWIR)。这些海脊代表了两个明显不同的超低扩张中心，其中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。岩石收集将与以前收集的地球物理数据(磁学、重力、多波束地图和地震数据)和新获得的从一组代表性样品中获得的电子显微数据相结合，以估计地壳和地幔岩石的化学成分。这些都将被用来估计洋壳的厚度和结构，并评估它们与海水和下伏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年收集的缓慢扩张的地壳岩石的整个集合的机会。这个项目是一个为期三年的研究计划，有几个重要的目标。首先，它将提供以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。作为这一档案的一部分，它将允许研究人员将描述性数据与该地区现有的地球物理、磁学和地球化学数据档案相结合。通过对两个超低扩张海脊-西南印度海脊(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，将增加新的化学成分数据。这项研究还将结合岩石学和地球化学数据，广泛收集SWIR的多波束地图和现有的地震、磁学和重力数据，以及沿山脊轴线和裂谷山脉进行的独特的全面岩石采样。其目的是验证这样的假设，即沿海脊的扩张中心不是由深部地幔柱支持的，而是由与新元古代莫桑比克大洋关闭有关的古岛弧和弧后盆地下的含水地幔熔融的枯竭残留物支持的。它还试图确定相关热点的来源，以及它们如何与西南红外海相互作用，现代海脊的地球化学和岩石学证明了这一点，以及从海底到热点及其共轭位置的离轴水深测量和磁学。此外，还将完成超低扩展Gakkel山脊的平行合成，首次详细分析该山脊的地质情况，该分析基于阿莫尔探险期间沿其绘制的1,000公里路段的190个成功的疏浚和岩石核心站。目前，对Amore数据的分析，包括水深测量，在很大程度上局限于熔岩和橄榄岩的同位素、主量元素和微量元素地球化学。这条脊线与超低的SWIR形成了近乎完美的对比。Gakkel海脊没有转换断层(SWIR有许多)，因此提供了一个独特的机会，在没有它们的情况下研究地球化学变化和岩浆分段的原因和程度，以及哪些特征是超低扩展所致，哪些特征需要转换。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、慢和超低扩散脊处的岩脉-辉长岩转变，为前者的岩脉-辉长岩转变处的浅熔透镜以及后者的普遍缺失提供直接证据。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.