ABR: A Deeper Investigation of Oceanic Spreading Center Magmatic Processes

洋壳占地球表面的三分之二，与更古老的陆壳不同，洋壳在大洋中脊不断形成，然后在大洋海沟的俯冲带循环回到地球深处。地球的这个形成和再循环系统？S洋壳不断地向生物圈补充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-S物理和化学演化，对海洋和大气组成以及生态系统的可持续性产生深远影响。非常重要的是洋壳本身的组成和结构，考虑到它在海洋下的位置，研究洋壳本身是特别困难的。该项目将使用海洋地球物理工具，特别是成像地球S内部的现代地震方法，研究洋壳的形成和先前海洋考察期间收集的高质量地震数据集的结构，以揭示形成洋壳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性研究人员，并在地震成像和解释技术以及专业发展方面培训和指导一名女性博士生。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内部断层图像？S。外展将利用海洋与地球科学与技术学院的开放日。海洋扩张中心科学中最不了解也最具争议的话题之一就是下部洋壳的形成。虽然上地壳通常是通过堤防和喷发侵位的，但对于下地壳是如何形成的，人们并没有普遍的共识。二十多年来，人们曾多次尝试将来自活动扩张中心的地球物理观测与从构造窗口到下地壳的岩石学和构造观测相一致。这项工作导致了关于下地壳形成的各种相互竞争的模型。这场争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。以前对活动扩张中心的下地壳进行的大多数地震研究大多是在许多年前用现在已经过时的数据和方法进行的。最近沿着东部刘扩展中心进行的高分辨率活动震源和共址的宽带地震实验为重新检查熔体供应和下部地壳形成提供了一个极好的机会。利用50多万个P波和S波的观测数据集，我们将进行地震层析成像和全波形分析，包括对岩浆系统及其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，并提供次轴向岩浆系统内熔体分布和热结构方面亟需的约束。这个项目将解决向地壳岩浆系统供应熔体和在其中储存熔体的基本问题，并使我们了解脊轴的冷却和从下地壳中提取热量的情况。高分辨率成像将使我们能够对熔体分数、熔体分布和下地壳和地幔的热结构施加定量限制。利用新的结果，我们将沿着扩张中心检验与地壳成因有关的特定假说的预测。

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.