Low Crustal Fluid Reservoirs in Ultramafic Cumulates of Kamchatka

IF 1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
A. G. Simakin, O. Yu. Shaposhikova
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Abstract

Based on published geophysical and petrological data, lower crustal fluid reservoirs have been proposed below the Klyuchevskoy Volcano, expressed as a low Vp/Vs anomaly. A high Vp/Vs anomaly under the proposed fluid reservoir is interpreted as a zone of magma accumulation. The localization of fluids in these reservoirs in the ductile lower crust can vary from isolated inclusions to filling of microfractures over a time scale of several months. Using a simplified poroelastic model, it is shown that the transition in the topology of pore space filled with fluid or melt can provide the observed changes in Vp/Vs in the anomalies of high and low values at a melt content of several vol % and fluid content less than 1 vol %, respectively. In zones of active volcanism, such as the Klyuchevskaya group of volcanoes (KGV), fluid reservoirs are localized in ultramafic cumulates formed during the early high-temperature stage of magma fractionation. Ultramafic xenoliths in the products of eruptions of the KGV and Avachinsky volcanoes, often interpreted as mantle rocks, formed at pressures of about 5 kbar or depths of about 18–20 km in accordance with two-pyroxene geo-thermobarometry and the content of volatiles in melt inclusions in olivine and spinel. When crossing by ascending magmas, the fluid-containing reservoir experiences mechanical failure and injects a certain amount of fluid into the magma, which then captures pieces of crushed magmatic cumulates. The composition of melt inclusions in olivine can reveal records of the magma-fluid interaction.

Abstract Image

堪察加半岛超镁铁质堆积中的低地壳流体储层
根据已发表的地球物理和岩石学资料,在克柳切夫斯基火山下方提出了下地壳流体储层,表现为低Vp/Vs异常。流体储层下的高Vp/Vs异常被解释为岩浆聚集带。在几个月的时间尺度上,这些韧性下地壳储层中流体的定位可能从孤立的包裹体到微裂缝的充填。利用简化的孔隙弹性模型,研究了流体或熔体填充孔隙空间拓扑结构的转变,可以分别在熔体含量为几vol %和流体含量小于1 vol %时观测到高、低值异常的Vp/Vs变化。在活火山带,如克柳切夫斯卡亚火山群(KGV),流体储层定位于岩浆分选早期高温阶段形成的超镁铁质堆积。根据双辉石地温压测量和橄榄石和尖晶石熔体中挥发物的含量,KGV和Avachinsky火山喷发产物中的超镁铁质包体通常被解释为地幔岩石,形成于约5 kbar的压力或约18-20 km的深度。当通过上升的岩浆穿越时,含流体的储层经历机械故障,并向岩浆中注入一定量的流体,然后将破碎的岩浆堆积物捕获。橄榄石中熔体包裹体的组成可以揭示岩浆-流体相互作用的记录。
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来源期刊
Petrology
Petrology 地学-地球科学综合
CiteScore
2.40
自引率
20.00%
发文量
27
审稿时长
>12 weeks
期刊介绍: Petrology is a journal of magmatic, metamorphic, and experimental petrology, mineralogy, and geochemistry. The journal offers comprehensive information on all multidisciplinary aspects of theoretical, experimental, and applied petrology. By giving special consideration to studies on the petrography of different regions of the former Soviet Union, Petrology provides readers with a unique opportunity to refine their understanding of the geology of the vast territory of the Eurasian continent. The journal welcomes manuscripts from all countries in the English or Russian language.
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