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首页> 外文期刊>Contributions to Mineralogy and Petrology >Differentiation and crystallization conditions of basalts from the Kerguelen large igneous province: an experimental study
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Differentiation and crystallization conditions of basalts from the Kerguelen large igneous province: an experimental study

机译：Kerguelen大火成岩省玄武岩的分化和结晶条件：实验研究

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Phase relations of basalts from the Kerguelen large igneous province have been investigated experimentally to understand the effect of temperature, fO2, and fugacity of volatiles (e.g., H2O and CO2) on the differentiation path of LIP basalts. The starting rock samples were a tholeiitic basalt from the Northern Kerguelen Plateau (ODP Leg 183 Site 1140) and mildly alkalic basalt evolved from the Kerguelen Archipelago (Mt. Crozier on the Courbet Peninsula), representing different differentiation stages of basalts related to the Kerguelen mantle plume. The influence of temperature, water and oxygen fugacity on phase stability and composition was investigated at 500 MPa and all experiments were fluid-saturated. Crystallization experiments were performed at temperatures between 900 and 1,160°C under oxidizing (log fO2 ~ ΔQFM + 4) and reducing conditions (log fO2 ~ QFM) in an internally heated gas-pressure vessel equipped with a rapid quench device and a Pt-Membrane for monitoring the fH2. In all experiments, a significant influence of the fO2 on the composition and stability of the Mg/Fe-bearing mineral phases could be observed. Under reducing conditions, the residual melts follow a tholeiitic differentiation trend. In contrast, melts have high Mg# [Mg2+/(Mg2+ + Fe2+)] and follow a calk-alkalic differentiation trend at oxidizing conditions. The comparison of the natural phenocryst assemblages with the experimental products allows us to constrain the differentiation and pre-eruptive conditions of these magmas. The pre-eruptive temperature of the alkalic basalt was about 950–1,050°C. The water content of the melt was below 2.5 wt% H2O and strongly oxidizing conditions (log fO2 ~ ΔQFM + 2) were prevailing in the magma chamber prior to eruption. The temperature of the tholeiitic melt was above 1,060°C, with a water content below 2 wt% H2O and a log fO2 ~ ΔQFM + 1. Early fractionation of clinopyroxene is a crucial step resulting in the generation of silica-poor and alkali-rich residual melts (e.g., alkali basalt). The enrichment of alkalis in residual melts is enhanced at high fO2 and low aH2O. Keywords Large igneous provinces - Basalt - Oxygen fugacity - Liquid lines of descent - Phase relations - Crystallization experiments Communicated by T. L. Grove.
机译：通过实验研究了克格伦大火成岩省的玄武岩的相关系，以了解温度，fO 2 和挥发物（例如H 2 O和CO）逸度的影响 2 ）在LIP玄武岩的分化路径上。起始岩样是来自北克尔格伦高原（ODP Leg 183 Site 1140）的胆统玄武岩和由克尔格伦群岛（库尔贝半岛的克罗齐尔山）演化出的轻度碱性玄武岩，代表了与克尔格伦地幔有关的玄武岩的不同分化阶段羽。在500 MPa下研究了温度，水和氧逸度对相稳定性和组成的影响，所有实验均处于流体饱和状态。在900到1,160°C的温度下在内部进行氧化（log fO 2 〜ΔQFM+ 4）和还原条件（log fO 2 〜QFM）进行结晶实验加热的气压容器，配有快速淬火装置和用于监测fH 2 的Pt膜。在所有实验中，都可以观察到fO 2 对含Mg / Fe矿物相的组成和稳定性的显着影响。在还原条件下，残余熔体遵循塑性分化趋势。相反，熔体具有较高的Mg＃[Mg 2 + /（Mg 2 + + Fe 2 + ）]，并且遵循小碱度在氧化条件下的分化趋势。天然表晶组合与实验产品的比较使我们能够限制这些岩浆的分化和喷发前的条件。碱性玄武岩的喷发前温度约为950–1,050°C。熔体中的水含量低于2.5 wt％H 2 O，喷发前岩浆室内普遍存在强氧化条件（log fO 2 〜ΔQFM+ 2） 。热塑性熔体的温度高于1,060°C，水含量低于2 wt％H 2 O，log fO 2 〜ΔQFM+ 1。亚油基吡啶是导致贫硅和富碱残渣（例如碱玄武岩）生成的关键步骤。在高fO 2 和低aH 2 O下，残余熔体中碱的富集得以增强。关键词大火成岩省-玄武岩-氧逸度-下降液体线-相关系-结晶实验由T. L. Grove通讯。

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