刚果民主共和国尼拉贡戈火山的水管系统结构和分化过程

IF 3.5 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
Sander M Molendijk, Olivier Namur, Ephrem Kamate Kaleghetso, Paul R D Mason, Benoît Smets, Jacqueline Vander Auwera, David A Neave
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引用次数: 0

摘要

尼拉贡戈火山(Nyiragongo volcano)是地球上碱含量最高的火山中心之一(一般为 Na2O + K2O >10 wt.%,琼脂指数高达 1.34),其特点是有一个半永久性的活跃熔岩湖,湖中有硅不饱和(SiO2 <40 wt.%)、低粘度的熔岩。为了增进我们对这一独特岩浆系统的了解,我们展示了一组在 2017 年至 2021 年期间新的实地考察中采集的 291 个样本。我们测量了所有样本的主要元素和痕量元素成分,揭示了从寄生锥喷出的原始皮孔岩(Mg# 82)到最近于 2002 年、2016 年和 2021 年从主火山口喷出的各种高度演化的辉长岩、白云岩和熔长岩的岩性范围。我们测量了所有取样岩性中矿物的主要和微量元素成分。根据这些数据,我们推算出尼拉贡戈的主要岩浆储层位于大约 9 - 15 千米和 21 - 33 千米深处,这与最近的地震观测结果一致。利用观测到的矿物成分和比例进行了分馏结晶建模,假定从橄榄石-麦饭石母熔体演化而来,将岩性与特定的残余液体组分定量联系起来。我们的建模表明,在深腔中形成的分馏积聚物将剩余的熔体部分减少到约60%,之后熔体被注入上部以液体为主的岩浆腔,在那里倩辉石、麦饭石和长石的分馏和积聚占主导地位。矿物纹理和地球化学特征显示,在一个反复充注的管道系统中,晶体具有很高的流动性,该系统分为液态为主的演化岩浆室和固态为主的原始岩浆室,液态成分随着深度的增加而减少。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Plumbing system architecture and differentiation processes of the Nyiragongo volcano, DR Congo
The Nyiragongo volcano is one of the most alkali-rich volcanic centres on the planet (Na2O + K2O generally >10 wt.%, agpaitic index up to 1.34), characterized by a semi-permanently active lava lake which hosts silica-undersaturated (SiO2 <40 wt.%), low viscosity lavas. To improve our understanding of this unique magmatic system, we present a set of 291 samples, acquired during new field excursions between 2017 and 2021. The major and trace element composition of all samples was measured, revealing a lithological range extending from primitive picrites (Mg# 82) erupted from parasitic cones to a variety of highly evolved nephelinites, leucitites, and melilitites erupted from the main edifice as recently as 2002, 2016, and 2021. We measured major and trace element compositions from the full spectrum of minerals present in all sampled lithologies. From these we calculated that the main magma reservoirs feeding Nyiragongo are at approximately 9 – 15 and 21 – 33 km depth, in agreement with recent seismic observations. Fractional crystallization modelling using observed mineral compositions and proportions was performed to quantitatively link the lithologies to specific residual liquid fractions assuming evolution from an olivine-melilite parental melt. Our modelling indicates that fractionation cumulate formation in deep chambers reduces the melt fraction remaining to ~60%, after which melts are injected into upper, liquid dominated magma chambers where fractionation and accumulation of clinopyroxene, melilite, and feldspathoids dominate. Characterisation of mineral textures and geochemistry reveals high crystal mobility in a repeatedly recharging plumbing system split between liquid-dominated, evolved magma chambers and more solid-dominated, primitive mushes, decreasing in liquid fraction with depth.
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来源期刊
Journal of Petrology
Journal of Petrology 地学-地球化学与地球物理
CiteScore
6.90
自引率
12.80%
发文量
117
审稿时长
12 months
期刊介绍: The Journal of Petrology provides an international forum for the publication of high quality research in the broad field of igneous and metamorphic petrology and petrogenesis. Papers published cover a vast range of topics in areas such as major element, trace element and isotope geochemistry and geochronology applied to petrogenesis; experimental petrology; processes of magma generation, differentiation and emplacement; quantitative studies of rock-forming minerals and their paragenesis; regional studies of igneous and meta morphic rocks which contribute to the solution of fundamental petrological problems; theoretical modelling of petrogenetic processes.
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