Formation Conditions of Ignimbrites of the Khangar Volcano (Kamchatka)

V. Simonov, A. Kotlyarov, A.A. Kotov, A. Perepelov, N. Karmanov, A. Borovikov
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Abstract

—The study of minerals, melt inclusions, as well as natural glasses showed that two different melts contributed to the formation of ignimbrites of the Khangar Volcano. The first, providing the information on melt inclusions in plagioclase and quartz phenocrysts, represents the state of magma in a deep source. The other type of melt is responsible for the formation of glasses and microcrystals of feldspars in fiamme. Experimental and analytical studies of melt inclusions showed that crystallization of most plagioclase and quartz phenocrysts from ignimbrites of the Khangar Volcano occurred at temperatures of 840–960 °C and pressures up to 1.1 kbar, from the melt with water contents up to 3.23 wt.%, under the conditions of magma chamber. The presence of syngenetic primary melt and fluid inclusions in plagioclase and quartz phenocrysts from ignimbrites of the Khangar Volcano indicates phase separation (“boiling”) of the melt with mass formation of СО2 microbubbles in magma. The other type of melt is secondary relative to magmatic systems of the Khangar Volcano and is formed by sintering and melting of tuffogenic volcanoclastic material. This melt contributed to the formation of fiamme in the examined ignimbrites. Based on the study of glasses and microcrystals of feldspars in fiamme, it was found that crystallization of oligoclase occurred at temperatures of 770–840 °C in the melt between the spherules (with water content up to 2.91 wt.%). Sanidine crystals grew over spherules at lower temperatures, 680–760 °C.
堪察加半岛汉加尔火山点燃岩的形成条件
-对矿物、熔体包裹体以及天然玻璃的研究表明,有两种不同的熔体促成了康加尔火山火成岩的形成。第一种熔体提供了斜长石和石英表晶中熔体包裹体的信息,代表了深源岩浆的状态。另一类熔体是岩浆中玻璃和长石微晶形成的原因。对熔体包裹体的实验和分析研究表明,在岩浆室条件下,康加尔火山火成岩中大部分斜长石和石英表晶的结晶发生在温度为 840-960 °C、压力高达 1.1 千巴的条件下,来自含水量高达 3.23 wt.%的熔体。在康加尔火山火成岩的斜长石和石英表晶中存在共生原生熔体和流体包裹体,这表明熔体相分离("沸腾"),在岩浆中大量形成СО2微气泡。另一种熔体相对于康卡尔火山的岩浆系统是次生的,是由凝灰岩成因的火山碎屑物质烧结熔化形成的。这种熔体在所考察的火成岩中促成了火成岩的形成。根据对 fiamme 中的玻璃和长石微晶的研究,发现在球粒(含水量高达 2.91 wt.%)之间的熔体中,低闪长岩的结晶温度为 770-840 ℃。在较低温度(680-760 °C)下,赛尼丁晶体生长在球状体上。
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