Determining the origin of Haxby lineaments using magnetotelluric and bathymetric data

深海海底的一个未解之谜是海底上方地球重力强度存在规则的波浪状波动。这些特征会定期重复出现，可以被绕地球运行的卫星清楚地探测到。形成重力波动的过程有三种理论：海洋地壳远离洋中脊并冷却时的海底破裂，地幔对流细胞或地壳下的熔融通道。该项目将通过在太平洋一个重力特征特别突出的地区获取地球物理数据，找出这些理论中哪一个是正确的--或者可能发现答案是完全出乎意料的。无论是什么引起的重力波动，答案将揭示更多关于我们的地球在海洋下面的动力学和板块构造如何工作。这项研究的目的是确定哈克斯比线性构造的起源，这是海洋岩石圈上方重力场的小，周期性波动，尽管几十年的研究，仍然是神秘的。该项目将在太平洋海盆马克萨斯群岛东北部200公里乘600公里的区域部署40台海底宽带大地电磁仪器，以测量岩石圈和软流圈地幔传导率的变化，并绘制海底地形图和声纳后向散射图。通过将电导率、水深测量和重力相关联，该项目将能够区分试图解释哈克斯比线性构造的多个竞争模型。拟议中的实验将有效区分三种假设：岩石圈的热收缩，软流圈中的小规模对流和软流圈回流通道。热收缩模型预测，水深测量应与重力滚动呈正相关，而不包括软流圈分量。小规模的对流和回流通道模型表明，重力线性的软流圈源-热，低密度地幔可探测的大地电磁数据-但不同的电导率异常与地形和重力。研究结果将有助于确定远离海脊或俯冲带的岩石圈-软流圈动力学的性质，包括较老岩石圈（42 Ma）下是否存在部分熔融。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

An unsolved mystery of the deep ocean seafloor is the presence of regular, wave-like fluctuations in the strength of Earth’s gravity above the seafloor. These features repeat over regular intervals and can be clearly detected by satellites orbiting the Earth. There are three theories for the processes forming the gravity fluctuations: seafloor cracking as ocean crust moves away from mid-ocean ridges and cools, mantle convection cells, or melt channels beneath the crust. This project will find out which of these theories is correct - or perhaps discover the answer is something altogether unexpected - by acquiring geophysical data at a region in the Pacific Ocean where the gravity features are particularly prominent. Regardless of what is causing the gravity fluctuations, the answer will reveal more about the dynamics of our planet beneath the oceans and how plate tectonics works.The objective of this study is to determine the origin of Haxby lineaments which are small, periodic undulations in the gravity field above oceanic lithosphere that, despite decades of study, remain mysterious. This project will deploy 40 ocean-bottom broadband magnetotelluric instruments to measure variations in mantle conductivity in the lithosphere and asthenosphere, and will map the seafloor topography and sonar backscatter, in a 200 km by 600 km area northeast of the Marquesas Islands in the Pacific Ocean basin. By correlating conductivity, bathymetry, and gravity, the project will be able to distinguish between multiple competing models attempting to explain the Haxby lineaments. The proposed experiment would effectively discriminate between three hypotheses: thermal contraction of the lithosphere, small-scale convection in the asthenosphere, and asthenospheric return flow channels. The thermal contraction model predicts that bathymetry should be positively correlated with the gravity rolls without an asthenospheric component. The small-scale convection and return flow channels models suggest an asthenospheric source of the gravity lineaments - hot, low-density mantle detectable by magnetotelluric data - but differ in how the conductivity anomalies correlate to topography and gravity. The results will help determine the nature of lithosphere-asthenosphere dynamics far from ridges or subduction zones, including whether there is partial melt beneath older lithosphere (42 Ma).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.