Collaborative Research: Developing a New Model to Investigate the Dynamics of Melt Generation beneath Mid-Ocean Ridges

全球洋中脊系统是地球上最大的火山系统。 洋脊轴下方上涌地幔减压产生的岩浆形成了洋壳，与岩浆侵位相关的热量驱动了生物活动和热液循环。这反过来又调节海洋和岩石圈之间的化学交换。这项研究开发了洋中脊下融化的模型和建模软件，以便预测（1）产生的熔体总量和（2）熔体的成分。这些信息对于预测海底火山喷发的类型以及确定元素和挥发物（例如二氧化碳）从地幔进入浅层地壳、海洋和大气的通量非常重要。 拟议的项目将为 MIT/WHOI 联合项目研究生和几位 WHOI 本科暑期学生提供支持。此外，为该项目开发的新软件将通过 NSF 资助的地球动力学计算基础设施 (CIG) 公开获取新软件的源代码，从而最大限度地提高研究的效用。这项研究开发了一种新的开源洋中脊玄武岩 (MORB) 融化模型，该模型具有增强的预测能力，可捕获融化的关键物理/热力学，并将该模型与其他 3D 地球动力学模型结合起来，以解决 MORB 成因中的突出问题。新模型将包括：(1) cpx-out 附近的熔化，(2) Cr-Al 尖晶石熔化反应，(3) 少量 H2O 对地幔熔化的影响，(4) 石榴石存在下的熔化，(5) 作为压力函数的可变熔化生产力，以及 (6) 跟踪微量元素浓度。 这些模型将用于利用过去二十年发表的各种实验数据。 与地球动力学模型相结合，熔化模型将用于研究地幔潜在温度、地幔成分以及大洋中脊熔体迁移的长度尺度和模式的局部和全球变化。由此产生的模型将用于：确定地幔温度、熔体生产力和地幔成分（包括挥发物）对洋中脊下方融化的相对作用；探索熔融区域的几何形状（受轴向热结构控制）和熔体迁移模式对地壳厚度和主量和微量元素化学等关键可观测值的影响；并研究高压分步结晶和熔壁岩石反应在控制 MORB 和深海橄榄岩化学成分中的相对作用。

The global mid-ocean ridge system is the largest volcanic system on Earth. Magma generated by decompression of upwelling mantle beneath the ridge axis creates the oceanic crust and the heat associated with magma emplacement drives biological activity and hydrothermal circulation. This, in turn, modulates chemical exchange between the oceans and the lithosphere. This research develops models and modeling software for melting beneath mid-ocean ridges in order to predict (1) the total amount of melt produced and (2) composition of the melts. Such information is important for predicting the style of volcanic eruption on the seafloor, as well as determining the flux of elements and volatiles (e.g., CO2) from the Earth?s mantle into the shallow crust, oceans, and atmosphere. The proposed project will provide support for an MIT/WHOI Joint Program graduate student and several WHOI undergraduate summer student fellows. In addition, the new software that will be developed for this project will maximize the utility of the research by making the source codes of the new software publicly accessible via the NSF-funded Computational Infrastructure for Geodynamics (CIG). This research develops a new, open-source mid-ocean ridge basalt (MORB) melting model with enhanced predictive capabilities that capture the key physics/thermodynamics of melting, and couples this model with other 3-D geodynamic models to address outstanding questions in MORB genesis. The new model will incorporate: (1) melting near cpx-out, (2) Cr-Al spinel melting reactions, (3) the effects of small amounts of H2O on mantle melting, (4) melting in the presence of garnet, (5) variable melt productivity as a function of pressure, and (6) tracking of trace element concentrations. The models will be used to exploit a wide range of experimental data published over the last two decades. Coupled with geodynamic models, the melting model will be used to investigate local and global variations in mantle potential temperature, mantle composition, and the length-scales and patterns of melt migration at mid-ocean ridges. Resulting models will be used to: determine the relative roles of mantle temperature, melt productivity, and mantle composition (including volatiles) on melting beneath mid-ocean ridges; explore the influence of the geometry of the melting region (as controlled by axial thermal structure) and the patterns of melt migration on key observables such as crustal thickness and major and trace element chemistry; and investigate the relative roles of high-pressure fractional crystallization and melt-wall rock reaction in controlling MORB and abyssal peridotite chemical compositions.