ABR: A Deeper Investigation of Oceanic Spreading Center Magmatic Processes

海洋地壳占我们地球的三分之二？与更古老的大陆地壳形成对比的是，它不断地在大洋中脊产生，然后在所谓的俯冲带的海沟处循环回到地球深处。 地球的形成和循环系统？海洋地壳不断地向生物圈提供维持生命的热量和元素。 记录这些过程和通量是我们理解地球的核心？海洋的物理和化学演变，对海洋和大气的组成以及生态系统的可持续性产生深远影响。 海洋地壳本身的组成和构造非常重要，由于其位于海洋之下，因此特别难以研究。 该项目将使用海洋地球物理工具，特别是现代地震方法，成像地球？利用以往海洋考察中收集的高质量地震资料，研究大洋地壳的形成和结构，揭示大洋地壳形成的板块边界岩浆系统和冷却岩浆系统的海底热液系统的性质。该项目将支持一名初级女研究员，并培训和指导一名女博士。地震成像和解释技术以及专业发展学生。夏威夷大学的本科生将与PI一起学习地球物理数据收集的基础知识，以及如何制作自己的地球断层图像？的内部。 外联活动将利用海洋和地球科学与技术学院的开放日。大洋扩张中心科学中最不为人所知和最有争议的话题之一是大洋下地壳的形成。 虽然上地壳通常是通过筑堤和喷发而就位的，但下地壳是如何形成的还没有普遍的共识。 二十多年来，人们一直试图将来自活跃扩张中心的地球物理观测结果与来自构造窗口的岩石学和构造观测结果相协调。 这项工作导致了各种各样关于下地壳形成的相互竞争的模型。 这场辩论的核心是下地壳和上地幔中熔体的数量和分布，这些地区的温度结构，以及可能有助于下地壳原位结晶的离轴冷却程度。 现代地震测量的相对缺乏阻碍了进展。 大多数以前对活跃扩张中心下地壳的地震研究主要是在多年前进行的，所用的数据和方法现在已经过时。 最近的高分辨率有源和共定位宽带地震实验沿着东刘扩展中心提供了一个极好的机会，重新检查熔体供应和下地壳的形成。 使用超过500，000个P和S波形观测的大型数据集，我们将进行地震层析成像和全波形分析，包括岩浆系统和周围地壳和地幔的全三维各向异性成像。 拟议的研究将成像下地壳和上地幔，并提供急需的限制熔体分布和热结构内的亚轴向岩浆系统。 该项目将解决熔体供应的基本问题，并在内部存储，地壳岩浆系统，以及告知我们的脊轴的冷却和从下地壳提取热量的理解。 高分辨率成像将使我们能够对熔体分数、熔体分布以及下地壳和地幔的热结构进行定量约束。 利用这些新的结果，我们将检验与沿着扩张中心的地壳成因有关的特定假设的预测。

Oceanic crust comprises two-thirds of our planet?s surface and, in contrast to the much older continental crust, is being continually created at mid-ocean ridges and then recycled back into the deep earth at ocean trenches at what are called subduction zones. This formation and recycling system of Earth?s oceanic crust continually replenishes life-sustaining heat and elements to the biosphere. Documenting these processes and fluxes is central to our understanding of the Earth?s physical and chemical evolution, with profound impacts on ocean and atmospheric composition, and the sustainability of ecosystems. Of significant importance is the composition and construction of the oceanic crust itself, which is uniquely difficult to study given its location under the oceans. The project will use marine geophysical tools, in particular modern seismic methods that image Earth?s interior, to investigate ocean crust formation and structure of a high quality seismic dataset collected during prior oceanographic expeditions, to reveal the properties of both the plate-boundary magmatic system where ocean crust forms and the seafloor hydrothermal systems that cool the magmatic systems. The project will support a junior female researcher and train and mentor a female Ph.D. student in seismic imaging and interpretation techniques as well as professional development. University of Hawaii undergraduate students will work with the PI to learn the basics of geophysical data collection and how to make their own tomographic images of the Earth?s interior. Outreach will take advantage of the School of Ocean and Earth Science and Technology open house. One of the least understood and most controversial topics of oceanic spreading center science is the formation of lower oceanic crust. While the upper crust is typically emplaced via diking and eruption, there is no general agreement how the lower crust forms. For over two decades there have been many attempts to reconcile geophysical observations from active spreading centers with petrologic and structural observations from tectonic windows into the lower crust. This work has led to a variety of competing models on lower crustal formation. Central to this debate are the amount and distribution of melt in the lower crust and uppermost mantle, the temperature structure of those areas, and the extent of off-axis cooling that could assist the in situ crystallization of the lower crust. The relative lack of modern seismic measurements impedes progress. Most previous seismic studies of the lower crust at active spreading centers were largely performed many years ago with data and methods that are now outdated. Recent high-resolution active-source and co-located broadband seismic experiments along the Eastern Lau Spreading Center present an excellent opportunity to re-examine melt supply and lower crustal formation. Using a large dataset of over 500,000 observations of P and S waveforms, we will perform seismic tomography and full waveform analyses, including full three-dimensional anisotropic imaging of the magmatic system and surrounding crust and mantle. The proposed research will image the lower crust and upper mantle, and provide much-needed constraints on melt distribution and thermal structure within the sub-axial magmatic system. This project will address fundamental questions of melt supply to, and storage within, the crustal magmatic system, as well as inform our understanding of the cooling of the ridge axis and the extraction of heat from the lower crust. The high resolution imaging will allow us to place quantitative constraints on melt fraction, melt distribution, and the thermal structure of the lower crust and mantle. With the new results we will test predictions of specific hypotheses related to crustal genesis along spreading centers.