Fully three-dimensional numerical models for along-axis variations in magmatic and tectonic processes at slow-spreading mid-ocean ridges

大洋核复合体（oceancorecomplex，OCCs）是近年来发现的一个有趣的现象。 当断层不断滑动并最终将下地壳和地幔岩石挖出到海底时，就会形成OCC。OCC不仅通过揭示深层岩石提供了对地球地幔的一瞥，而且它们通常有与之相关的热液喷口，这些喷口拥有大型生态系统。当首次发现时，OCC被认为主要形成于岩浆供应较低的缓慢扩张的洋中脊段的末端附近。然而，它们也被发现在远离传播段末端的位置。 此外，在某些地方，OCC的形成与正常的海底扩张交替发生，从而产生短暂的断层。目前还不清楚是什么控制着交替断层的样式。该项目将制作一个三维力学模型，以了解大洋中脊OCC形成的控制因素。 总体目标是了解断层在海洋盆地形成和演化中的作用。该项目将招募本科生参与研究，优先确定传统上在科学领域代表性不足的群体的参与者。将制作解释模型和模型结果的电影，并将用于研究生课程，并适用于K-12学校。在缓慢扩张的洋中脊，筑堤频率和断层样式变化很大，在某种程度上彼此相关。 然而，我们对相关性背后的机制以及控制断裂样式的其他因素的理解仍然是不完整的。本项目的目标是建立机制，确定断层风格的空间和时间变化的脉频率在缓慢扩张的山脊，并量化的机制的灵敏度断层润滑过程和岩浆挤出和底镀扩张中心。该项目提议通过扩展现有的二维方法来开发一种三维建模方法，该方法已成功地解释了洋中脊横轴部分筑堤频率方面的主要形态和结构特征。全三维数值模型纳入沿轴的机械负荷所产生的变化，在筑堤和断层。此外，该建模方法还考虑了影响断层类型的其他重要因素，如断层面上形成的弱矿物的润滑作用。 四套数值实验将进行的顺序增加的复杂性。

The recent observations of oceanic core complexes (OCCs) are intriguing. OCCs are formed when faults keep slipping and eventually exhume lower crust and mantle rocks onto the seafloor. OCCs not only provide a glimpse into Earth's mantle by uncovering deep-seated rocks, but they commonly have hydrothermal vents associated with them which host large ecosystems. When first discovered, OCCs were assumed to form primarily near the ends of slow-spreading mid-ocean ridge segments where magma supply is low. However, they also have been found at locations far from spreading segment ends. Moreover, in some place the formation of OCCs alternates with normal seafloor spreading which produces short-lived faults. It is unclear what controls the alternating faulting styles. This project will produce a three-dimensional mechanical model to understand the controls on the formation of OCCs at mid-ocean ridges. The overarching goal is to understand the role of faulting in the formation and evolution of the ocean basins. The project will recruit undergraduate students to participate in the research with a priority on identifying participants from groups traditionally underrepresented in the sciences. Movies will be generated explaining the model and model results and will be used in graduate courses and adapted for use in K-12 schools.Diking frequencies and faulting styles are highly variable at slow-spreading mid-ocean ridges and correlated with each other to some degree. However, our understanding of the mechanism behind the correlation and other factors controlling faulting styles is still incomplete. The objectives of this project are to establish the mechanism that determines faulting styles in response to spatially and temporally varying diking frequencies at slow-spreading ridges and to quantify the sensitivity of the mechanism to fault-lubricating processes and magma extrusion and under-plating at spreading centers. The project proposes to develop a three-dimensional (3D) modeling approach by extending an existing two-dimensional (2D) method that has been successful in explaining the main morphological and structural features in across-axis sections of mid-ocean ridges in terms of diking frequencies. The fully 3D numerical models incorporate the along-axis mechanical loading arising from variability in diking and faulting. Furthermore, the modeling method will consider other important factors affecting faulting styles such as lubrication effects of frictionally weak minerals forming on fault surfaces. Four suites of numerical experiments will be conducted in the order of increasing complexity.