Collaborative Research: The four-dimensional distribution of magmatism during the growth of lower oceanic crust: High precision U-Pb dating of IODP Hole U1473A, Atlantis Bank, SWIR

虽然海洋盆地占地球表面的70%以上，但我们对海底地壳的下部是如何随着时间的推移而演变的，在起源于洋中脊喷发的熔岩或通过海洋核复合体的逆冲断层和翻滚之后，它们是如何变厚和冷却的，我们知之甚少。由于这种物质构成了地壳的大部分下沉部分，在俯冲带中被地幔吞噬，这是世界上绝大多数地震和火山的发生地，因此了解这部分地壳岩石圈的结构、组成和演化对科学知识和灾害风险分析都很重要。为了更多地了解这部分海洋地壳，国际海洋发现计划（International ocean Discovery Program）于2015-2016年在西南印度洋山脊的亚特兰蒂斯滩（Atlantis Bank）进行了一项由社区推动的重大努力，在海底岩石岩上钻深孔。来自世界各地的30多名科学家参与了这项工作。本研究的目的是确定构成下洋壳的侵入体的大小、形状和时间，确定它们的空间序列和尺寸。样品来自最近的海洋钻探腿上钻取的岩心。还将分析以前在附近钻取的岩心样本，并将其与新孔的岩心样本进行比较，以了解火成岩侵入体的空间连续性。为了实现研究目标，将利用锆石的高精度铀铅（U-Pb）测年来了解海洋盆地下地壳吸积期间岩浆活动的时间和空间分布。锆石是一种一旦形成就不会发生蚀变的矿物。正如其他最近的研究所显示的那样，这些数据允许识别单个的侵入事件，这些事件可以提供对下部海洋地壳的构造尺寸和历史的限制，并表明侵入体的冷却速度。从亚特兰蒂斯海岸钻取的789米长的岩心中提取的90多个样本将使用同位素稀释热电离质谱法进行分析。关于锆石中铪的其他同位素工作将在爱达荷州的一个姊妹机构（博伊西州立大学）进行。这项工作的广泛影响是多方面的，包括两个EPSCoR州（分别为怀俄明州和爱达荷州）的机构（怀俄明大学和博伊西州立大学）的两名教师和一名研究人员的支持，其中EPSCoR表示与其他州相比，没有显著的联邦支出。其他影响包括研究生培训（其中一名是来自中国的交换生，免费参与该奖项）、怀俄明州和加利福尼亚州的中学和高中推广活动，以及开发用于整合U-PB和微量元素数据的新软件。这项研究也是大型多国海洋钻探计划的一部分，涉及重要的国际合作。

Although ocean basins make up over 70% of the Earth's surface, our knowledge of how the lower portions of the underlying ocean crust evolves over time, thickening and cooling after originating as erupting lavas in mid-ocean ridges or via thrust faulting and roll over in oceanic core complexes is poorly known. Because this material makes up the bulk of the down-going portion of the crust consumed into the mantle in subduction zones, which are the loci of the vast majority of the world's earthquakes and volcanoes, understanding the structure, composition, and evolution of this part of the crustal lithosphere is important for both scientific knowledge and disaster risk analysis. To learn more about this part of the ocean crust, a major community-driven effort to drill deep bore holes into magmatic rocks on the seafloor by the International Ocean Discovery Program, an effort involving more than 30 scientists from around the world, was carried out in 2015-2016 on the Southwest Indian Ridge at a location called the Atlantis Bank. Goals of this research are to determine the size and shape and timing of the intrusive bodies that make up the lower ocean crust, their spatial sequence, and their dimensions. Samples come from the core drilled on the recent ocean drilling leg. Samples from a previously drilled core in the general vicinity will also be analyzed and compared to those from the new hole to get an idea of the spatial continuity of the igneous intrusive bodies. To accomplish research goals, high-precision Uranium-Lead (U-Pb) dating of zircons, a mineral resistant to alteration once it is formed, will be used to provide insights into the time and space distribution of magmatism during lower crustal accretion in the ocean basins. As shown by other recent studies, these data permit the recognition of individual intrusive events that can provide constraints on the constructional dimensions and history of the lower oceanic crust and indicate the cooling rates of the intrusive bodies. Over 90 samples from the 789 meter-long core drilled into the Atlantis Bank will be analyzed using isotope-dilution thermal ionization mass spectrometry. Additional isotopic work on Hafnium in the zircons will be carried out at a sister institution in Idaho (Boise State University). Broader impacts of the work are multi-faceted and include support of two faculty and one researcher at institutions (University of Wyoming and Boise State University) in two EPSCoR states (Wyoming and Idaho, respectively) where EPSCoR indicates a state in which there is no significant federal spending compared to other states. Additional impacts include graduate student training, one of whom is an exchange student from China and involved at no cost to this award, middle and high school outreach in both Wyoming and California, and the development of new software for the integration of U-PB and trace element data. The study is also part of the large, multi-national Ocean Drilling Program and involves significant international collaboration.