Deciphering the Origin of Intra-Plate Volcanism in the Pacific Northwest Using Geodynamic Models with Data Assimilation

我们建议探讨太平洋西北部板内火山岩省的成因，包括中中新世斯蒂恩斯-哥伦比亚河泛滥玄武岩以及随后的黄石和纽贝里热点轨迹。我们将测试的可能机制包括起源于核-地幔边界的地幔热柱，以及来自浅地幔过程的火山作用，如板片驱动的上升流。除了地质观测外，我们还强调更好地约束深部地幔动力学，包括地幔流动的模式和太平洋西北下方缓慢地震异常的性质。我们的方法是数据同化的四维地球动力学模拟，它包括高分辨率的正向俯冲模拟和重建过去地幔状态的伴随对流计算。重要的模型约束来自于USArrow揭示的大幅改善的地幔结构和北美西部地下众所周知的新生代俯冲历史。这一提议试图解决科学界长期争论的一个问题：远离活动构造板块边界的火山活动的形成。由于存在1600万年前哥伦比亚河泛滥玄武岩的大规模喷发和正在进行的黄石-纽伯里热点火山等火山活动，太平洋西北部是一个理想的研究区域。这些火山事件的起源仍然难以捉摸，因为我们对这些火山活动起源的深部地幔结构的了解很差。现在，随着美国阵列地震实验最终描绘出次大陆地幔的三维图像，更好地了解太平洋西北火山活动的形成成为可能。为了解决这个看似复杂的问题，我们将依靠基于强大的超级计算机的复杂的数值模型。这些模型不仅将考虑地表地质记录，还将考虑地下的地幔结构，最重要的是自遥远的过去以来该系统的时间演化。从科学上讲，这项拟议的工作几乎影响到固体地球研究的所有领域。这项研究的另一个重要意义是增进对自然灾害的形成及其对气候和环境的影响的认识。

We propose to investigate the origin of the intra-plate volcanic province in Pacific Northwest, with features including the mid-Miocene Steens-Columbia River flood basalt and subsequent Yellowstone and Newberry hotspot tracks. Possible mechanisms we will test include a mantle plume originating from the core-mantle boundary, and volcanism from shallow mantle processes such as slab-driven upwelling flow. Besides geological observations, we emphasize on better constraining deep mantle dynamics including the pattern of mantle flow and the nature of slow seismic anomalies beneath the Pacific Northwest. Our approach is 4-D geodynamic modeling with data assimilation, which involves both high-resolution forward subduction simulations and adjoint convection calculations reconstructing past mantle states. Important model constraints come from the much improved mantle structure revealed by USArray and the well understood Cenozoic subduction history beneath western North America. This proposal attempts to solve for a long-debated issue in the scientific community: formation of volcanisms far away from active tectonic plate boundaries. The Pacific Northwest represents an ideal study region due to the existence of such volcanisms as the voluminous eruption of Columbia River flood basalt ~16 million years ago and the ongoing Yellowstone-Newberry hotspot volcanoes. Origin of these volcanic events has remained elusive because of our poor understanding on the configuration of deep mantle where these volcanisms originate. Now with the USArray seismic experiment finally delineating a 3-dimentional picture of the sub-continental mantle, a better understanding on the formation the Pacific Northwest volcanism becomes possible. To solve this apparently complex problem, we will rely on sophisticated numerical models based on powerful supercomputers. These models will take into account not only surface geologic records, but also the mantle structures underneath, and most importantly the time-evolution of the system since the remote past. Scientifically, the proposed work has impacts on almost every field of solid Earth research. Another important implication of this research is to improve knowledge on the formation of natural hazards and their effects on climate and environment.