加拿大不列颠哥伦比亚省米格火山群全新世玄武岩爆发前历史的橄榄石时间胶囊约束

IF 3.5 2区 地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS
S M Aufrère, G Williams-Jones, S Moune, D J Morgan, N Vigouroux, J K Russell
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引用次数: 0

摘要

卡斯卡特火山弧加拿大段(即加里波第火山带)由 100 多个喷发中心组成,跨越整个第四纪(更新世到全新世),沉积物的成分从碱性玄武岩到流纹岩不等。目前至少有一座火山是活火山;米格山(Mount Meager / Q̓welq̓welústen)曾于公元前 2360 年爆发,目前仍有炽热活动。对火山爆发频率和方式的长期预测取决于对以前火山爆发前岩浆过程的历史和时间尺度的重建。利用扩散年代测定法,我们对米格火山群进行了研究,重点是全新世橄榄石-斑岩玄武岩(利卢埃特冰川玄武岩),这些玄武岩是由利卢埃冰川退缩暴露出来的。我们在淬火玻璃质玄武岩熔岩样本中发现了两种不同的橄榄石群,它们记录了不同的岩浆过程和历史。由Fo83橄榄石表晶组成的团晶,由热的岩浆输入所夹带和搬运,形成族群1。这些岩浆表现出重吸收和 Fo76-78 最外缘成分的正常分带;其中三分之一的岩浆还表现出内部反向成分分带。第二组骨架微晶的成分与表晶边缘(即 Fo76-78)相同,并与邻近的基质玻璃处于平衡状态。我们估计,对于 H2O 含量为 0.5-1 wt.%的熔体,浅层储层(100 兆帕;约 3 千米)的爆发前温度-FO2 条件分别为约 1097-1106°C (± 30°C)和 NNO + 0.5 (±1.1)。利用这些输入参数,我们报告了来自 81 个橄榄石表晶的 234 个正常分带剖面的铁镁扩散计时结果。定向晶体中成分剖面的扩散模型表明,爆发前岩浆的停留时间为 1 到 3 个月。喷发前在浅储层中的停留时间极短,这表明未来喷发前可能会出现极短的动荡期。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Olivine Time-Capsules Constrain the Pre-Eruptive History of Holocene Basalts, Mount Meager Volcanic Complex, British Columbia, Canada
The Canadian segment of the Cascade Volcanic Arc (i.e. the Garibaldi Volcanic Belt) comprises more than 100 eruptive centres, spanning the entire Quaternary period (Pleistocene to Holocene in age), and with deposits ranging in composition from alkaline basalt to rhyolite. At least one of the volcanoes is currently active; Mount Meager / Q̓welq̓welústen erupted explosively 2360 years BP and has ongoing fumarolic activity. Long-term forecasting of eruption frequency and style depends on reconstruction of the history and timescales of magmatic processes preceding previous volcanic eruptions. Utilising diffusion chronometry, we investigate the Mount Meager Volcanic Complex focusing on Holocene olivine-phyric basalts (Lillooet Glacier basalts) exposed by the retreat of the Lillooet Glacier. We identify two distinct olivine populations in samples of quenched, glassy basalt lavas that record different magmatic processes and histories. Glomerocrysts of Fo83 olivine phenocrysts, entrained and transported by a hot mafic input, form Population 1. These exhibit resorption and normally zoned outermost rim compositions of Fo76–78; a third of them also show interior reverse compositional zoning. A second population of skeletal microphenocrysts have the same composition as the phenocryst rims (i.e. Fo76–78) and are in equilibrium with the adjacent matrix glass. We estimate the pre-eruptive temperature-fO2 conditions in a shallow reservoir (100 MPa; ~3 km) for a melt with H2O content of 0.5–1 wt.% as ~1097–1106°C (± 30°C), and NNO + 0.5 (±1.1), respectively. Using these input parameters, we report Fe-Mg diffusion chronometry results for 234 normally zoned profiles from 81 olivine phenocrysts. Diffusion modelling of compositional profiles in oriented crystals indicates pre-eruptive magmatic residence times of 1 to 3 months. These remarkably short residence times in shallow reservoirs prior to eruption suggest very short periods of unrest may precede future eruptions.
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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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