Near Solidus Partial Melting of Garnet Peridotite and the Origin of Alkali Olivine Basalt

碱性玄武岩和相关岩石（碧玄岩、霞石）是大洋岛屿和海山下岩浆作用的常见产物，但对它们的起源知之甚少。 由于这些岩石包含有关地球地幔中地球化学和地球动力学过程的关键信息，因此对这些岩石起源的限制对于更广泛地了解地球内部至关重要。解决有关板内玄武岩的动力学起源的争论需要限制岩浆成分与温度、压力和来源成分之间的关系。以往的实验研究未能再现的主要元素组成的碱性洋岛玄武岩（OIB）的橄榄岩+/-CO2的部分熔体。这意味着实验没有在正确的条件下进行，或者在OIB的来源中需要额外的（辉石岩或交代橄榄岩）岩性。 对这些可能性的评估需要新的实验来确定石榴石橄榄岩+/-CO2初始部分熔融过程中产生的液体的成分和比例。如果碱性玄武岩起源于石榴石橄榄岩的小程度熔融，并且如果熔融的温度和压力可以受到可能的母体液体的主要元素化学的限制，实验将把OIB的岩石学特征与熔融深度和源区地幔位温联系起来。本项目的目标是确定富产石榴石橄榄岩在其固相线处及其附近的部分熔体的成分，范围为0 - 5%。在3至7 GPa的压力下熔化。 计划采用改进的迭代三明治实验（MISE），其目的是准确地确定非常低的熔体分数熔体的组成。 这些技术将允许测定石榴橄榄岩的小程度熔体，这可能是板内岩浆活动的重要来源，但由于难以分析高温，高MgO部分熔体，实验数据很少。该团队还将使用MISE方法，通过对CO2浓度（0.1重量%）的橄榄岩进行实验，确定CO2对石榴石橄榄岩近固相线熔融的影响。接近于天然碱性玄武岩源区的那些。

Alkali basalts and related rocks (basanites, nephelinites) are common products of magmatic processes beneath oceanic islands and seamounts, but their origin is poorly understood. Because such rocks hold key information about geochemical and geodynamical processes in Earth's mantle, constraints on the origins of such rocks are critical to a broader understanding Earth's interior. Resolving debate regarding the dynamical origin of intraplate basalts requires constraints on the relationship between the compositions of magmas and the temperatures, pressures, and compositions of their sources. Previous experimental studies have failed to reproduce major element compositions of alkalic oceanic island basalts (OIB) from partial melts of peridotite+/-CO2. This means either that experiments have not been conducted under the right conditions or that an additional (pyroxenitic or metasomatized peridotitic) lithology is required in the source of OIB. Evaluation of these possibilities requires new experiments to determine the compositions and proportions of liquids generated during incipient partial melting of garnet peridotite+/-CO2 If alkali basalts originate from small-degree melting of garnet peridotite, and if the temperature and pressure of melting can be constrained by major element chemistry of plausible parental liquids, the experiments will relate the petrologic character of OIB to the depth of melting and mantle potential temperature in their source.This project has a goal to determine the compositions of partial melts of fertile garnet peridotite at and near its solidus from 0 to 5% melting at pressures of 3 to 7 GPa. It is planned to employ modified iterative sandwich experiments (MISE), which are designed to determine accurately the composition of very low melt fraction melts. These techniques will allow determination of small-degree melts of garnet peridotite, which may be important sources of intraplate magmatism, but for there are few experimental data, owing to difficulties in analyzing high temperature, high MgO partial melts. The team will also use the MISE method to determine the influence of CO2 on near-solidus melting of garnet peridotite by conducting experiments with peridotite with CO2 concentrations (0.1 wt.%) close to those likely in natural alkali basalt source regions.