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。 洋脊轴下上涌地幔减压产生的岩浆形成洋壳，岩浆侵位产生的热量驱动生物活动和热液循环。这反过来又调节了海洋和岩石圈之间的化学交换。本研究开发了大洋中脊下融化的模型和建模软件，以预测（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的通量（例如，CO2从地球？地幔进入浅地壳，海洋和大气。 拟议的项目将为麻省理工学院/WHOI联合项目研究生和几个WHOI本科暑期学生研究员提供支持。此外，将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）熔融模型，具有增强的预测能力，捕获熔融的关键物理/热力学，并将该模型与其他3-D地球动力学模型相结合，以解决MORB成因中的突出问题。新模型将包括：（1）cpx-出附近的熔融，（2）铬铝尖晶石熔融反应，（3）少量的H2O对地幔熔融的影响，（4）在石榴石存在下的熔融，（5）作为压力函数的可变熔体生产率，和（6）跟踪微量元素浓度。 这些模型将用于利用过去二十年来发表的广泛的实验数据。 与地球动力学模型相结合，熔融模型将用于调查地幔潜在温度、地幔成分以及洋中脊熔融物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的相对作用（包括挥发物）对洋中脊下融化的影响;探讨融化区几何形状的影响（受轴向热结构控制）和熔体迁移模式对地壳厚度和主要及微量元素化学等关键观测量的影响;探讨了高压分离结晶和熔体-围岩反应在控制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.