Magma Differentiation, Contamination/Mixing and Eruption Modulated by Glacial Load—The Volcanic Complex of The Pleiades, Antarctica

IF 2.9 2区 地球科学 Q2 GEOCHEMISTRY & GEOPHYSICS Geochemistry Geophysics Geosystems Pub Date : 2024-07-22 DOI:10.1029/2024GC011509
Samuele Agostini, Noemi Leone, John L. Smellie, Sergio Rocchi
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Abstract

The Pleiades Volcanic Field is made up of some 20 monogenetic, partly overlapping scoria and spatter cones, erupted in the last 900 ka, cropping out from the ice close to the head of the Mariner Glacier in northern Victoria Land, Antarctica. Erupted products vary from hawaiite to trachyte, defining a complete mild Na-alkaline differentiation trend. Mafic samples are characterized by multi-elemental patterns typical of OIB magmas, moderately low 87Sr/86Sr (0.7037) and high 143Nd/144Nd (0.51284), with a clear within-plate affinity, indicating a subcontinental lithospheric source. With increasing SiO2, 87Sr/86Sr ratios increase up to 0.7052 and 143Nd/144Nd decrease to 0.51277, supporting the hypothesis of open-system evolution, with significant crustal assimilation during fractional crystallization. The erupted volume of most evolved products (∼7 km3), according to fractionation models, suggests that primitive magmas should have been more than 10 times larger, indicating the occurrence of a large magma plumbing system, unexpected for a volcanic field of monogenetic scoria cones. The occurrence of a complete fractionation trend with large magma chambers and large assimilation rate is unusual, if not unique, among the alkali basaltic volcanic fields and it is matched by a climax of activity during the last glacial maximum (30 ka), as indicated by new 40Ar-39Ar ages (30 ± 3 ka and 25 ± 2 ka) for samples from the two most prominent edifices. Therefore, we hypothesize a role of a thick ice cap in suppressing eruptions and ultimately leading to prolonged magma residence time in the subsurface, favoring significant fractionation coupled with unusual high rates of crustal assimilation.

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岩浆分异、污染/混合和喷发受冰川负荷调节--南极洲昴宿星团火山群
昴宿星团火山区由大约 20 个单源、部分重叠的焦岩和喷溅锥组成,在过去 900 ka 年间喷发,从南极洲维多利亚陆地北部水手冰川头附近的冰层中喷发出来。喷发产物从哈威岩到闪长岩不等,形成了完整的温和钠碱分化趋势。镁质样品具有典型的 OIB 岩浆多元素模式,87Sr/86Sr(0.7037)和 143Nd/144Nd(0.51284)含量适中偏低,具有明显的板块内亲缘关系,表明其来源于次大陆岩石圈。随着二氧化硅的增加,87Sr/86Sr 比值上升到 0.7052,143Nd/144Nd 下降到 0.51277,这支持了开放系统演化的假说,在碎裂结晶过程中地壳同化显著。根据分馏模型,大部分演化产物的喷发体积(∼7 km3)表明,原始岩浆的体积应该是其10倍以上,这表明出现了一个大型岩浆管道系统,这对于一个由单源焦圆锥组成的火山区来说是意想不到的。在碱性玄武岩火山群中,出现具有大岩浆室和大同化率的完整分馏趋势即使不是独一无二的,也是不寻常的,与之相匹配的是最后一个冰川最盛时期(30 ka)的活动高潮,两个最突出火山口样本的新 40Ar-39Ar 年龄(30 ± 3 ka 和 25 ± 2 ka)表明了这一点。因此,我们假设厚厚的冰盖在抑制火山爆发方面发挥了作用,并最终导致岩浆在地下停留时间延长,有利于显著的分馏和不寻常的高地壳同化率。
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来源期刊
Geochemistry Geophysics Geosystems
Geochemistry Geophysics Geosystems 地学-地球化学与地球物理
CiteScore
5.90
自引率
11.40%
发文量
252
审稿时长
1 months
期刊介绍: Geochemistry, Geophysics, Geosystems (G3) publishes research papers on Earth and planetary processes with a focus on understanding the Earth as a system. Observational, experimental, and theoretical investigations of the solid Earth, hydrosphere, atmosphere, biosphere, and solar system at all spatial and temporal scales are welcome. Articles should be of broad interest, and interdisciplinary approaches are encouraged. Areas of interest for this peer-reviewed journal include, but are not limited to: The physics and chemistry of the Earth, including its structure, composition, physical properties, dynamics, and evolution Principles and applications of geochemical proxies to studies of Earth history The physical properties, composition, and temporal evolution of the Earth''s major reservoirs and the coupling between them The dynamics of geochemical and biogeochemical cycles at all spatial and temporal scales Physical and cosmochemical constraints on the composition, origin, and evolution of the Earth and other terrestrial planets The chemistry and physics of solar system materials that are relevant to the formation, evolution, and current state of the Earth and the planets Advances in modeling, observation, and experimentation that are of widespread interest in the geosciences.
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