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

石榴石橄榄岩近固相线部分熔融与碱橄榄石玄武岩成因

• 批准号: 0609967
• 负责人: Marc Hirschmann
• 金额: --
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-07-01 至 2010-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0609967&HistoricalAwards=false
• 关键词: Near; Solidus; Partial; Melting; Garnet

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.

碱性玄武岩和相关岩石（底石，侄子）是海洋岛屿和封口下的岩浆过程的常见产物，但它们的起源知之甚少。 由于这样的岩石在地球地幔中拥有有关地球化学和地球动力学过程的关键信息，因此对这种岩石起源的限制对于更广泛的理解地球内部至关重要。解决有关板岩内玄武岩的动态起源的辩论需要限制岩浆组成与其来源的温度，压力和组成之间的关系。先前的实验研究未能从橄榄岩+/- CO2的部分熔体中繁殖碱性海洋底层（OIB）的主要元素组成。这意味着要么在正确的条件下尚未进行实验，要么在OIB​​来源中需要额外的（辉石或交代植物植物）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石在初步的部分融化过程中产生的液体的组成和比例，如果碱基质底层碱底层质量小小的碱性质量的小度源于橄榄石的小度融化，以及如果融化的温度和液化的液态均可限制，那么液化的液态性化学效果是可限制的。 OIB到其来源中熔化和地幔电势温度的深度。该项目的目标是确定肥沃的石榴石橄榄岩在其固体菌群和附近的部分融化，其固体矿物质的固体速度从0到5％至5％，在3到7 GPA的压力下熔化。 计划采用经过改进的迭代三明治实验（MISE），该实验旨在准确确定非常低的熔体分数熔体的组成。 这些技术将允许测定小石榴石橄榄石的小度熔体，这可能是板岩内岩浆的重要来源，但由于很少有实验数据，这是由于很难分析高温，高温MGO的部分融化。该团队还将使用MISE方法来确定CO2对石榴石橄榄岩近西甲醇熔化的影响，该实验用橄榄岩具有二氧化碳浓度（0.1 wt。％）的实验，接近天然碱性玄武岩源区域的浓度接近。