The Colima Volcanic complex, Mexico
The Colima Volcanic complex, Mexico
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DOI：
10.1007/bf00374707
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发表时间：
1980-03
影响因子：
3.5
通讯作者：
J. Luhr;I. Carmichael
中科院分区：
文献类型：
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作者：
J. Luhr;I. Carmichael
Volcán科利马是墨西哥历史上最活跃的安山岩复合火山。它位于墨西哥火山带西端的中美洲海沟以北150公里处，比墨西哥任何其他复合火山都更接近海沟。自从1576年有记载的最早喷发以来，V. Colima火山经历了三个活动周期的演变。每个周期的高潮都是一次大的火山灰喷发，停止活动50年或更长时间。最后一次大规模的火山灰喷发发生在1913年。1961-1962年和1975-1976年的安山岩块状熔岩喷发标志着第四个历史周期活动的开始，这个周期也可能以下个世纪初的一次大的火山灰喷发而结束。本文介绍了一套9个破火山口后角闪岩和橄榄安山岩的全岩样品和所有组成相的主要元素和微量元素分析。该套件包括科利马自1869年以来的四次大喷发的样本，跨越了最后两个喷发周期。科利马的破火山口后安山岩缺乏K和其他不相容元素（Ti、P、Zn、Rb、Y、Zr、Ba、La、Yb、Hf、Th和U），这可能是近海沟安山岩的特征。从1913年的火山灰喷发到第四旋回安山岩，整个岩石的Si、Ba和Cs丰度增加，而Ti、Fe、Mg、Ni、Cr和Sc丰度减少。晶体分选模型可以很好地再现破火山口后组合中主要元素的变化，但系统地不能预测相容的微量元素Cr、Ni和Zn的足够浓度。科利马安山岩中相容微量元素的异常富集可能反映了次火山体系中晶体分选作用和岩浆混合作用的同步发生。角闪石安山岩的喷发前温度估计在940°- 1000°C之间，橄榄石安山岩的喷发前温度估计在1030°- 1060°C之间。角闪安山岩喷发前岩浆含水量为1.0 ~ 3.6 wt.%；橄榄岩-安山岩的斑晶组合计算为在1,000 bar含0.8% H2O时达到平衡。1961年以前所有样品的正辉石岩和某些斜辉石岩呈逆分带，边缘相对富镁。最明显的富镁边缘出现在橄榄岩-安山岩中，被认为反映了爆发前岩浆的混合，包括一种碱性的橄榄石+/-斜辉石质岩浆。1961年后的第四旋回安山岩除了具有正常分带的辉石岩外，还显示出许多其他特征，这些特征使它们与早期的破火山口后的角闪安山岩区别开来。这包括：(1)较高的总晶体含量；(2)较低的模态角闪石含量；(3)较高的喷发前硅活度；(4)较低的喷发前水含量。这些特征都与第四旋回安山岩在喷发前含水较少的解释相一致。1961年前角闪安山岩的微富镁辉石边缘可能记录了岩浆水含量在喷发前晚期的增加，这提高了熔体和所有结晶相中岩浆的fo2和Mg/Fe+2比值。第四旋回安山岩显然没有经历强烈的喷发前水流入，导致岩浆含水量较低，辉石岩通常呈带状分布。
Volcán Colima is Mexico's most historically active andesitic composite volcano. It lies 150 km north of the Middle America Trench at the western end of the Mexican Volcanic Belt, closer to the trench than any other composite volcano in Mexico. Since its earliest reported eruption in 1576, V. Colima has evolved through three cycles of activity. Each cycle culminated in a major ashflow eruption, halting activity for 50 or more years. The last major ashflow eruption occurred in 1913. Andesitic block lava eruptions in 1961–1962 and 1975–1976 marked the inception of activity in a fourth historical cycle which may also terminate with a major ashflow eruption in the early part of the next century.Major and trace element analyses of whole rock samples and all constituent phases are presented for a suite of nine post-caldera hornblende and olivine-andesites. The suite includes samples from Colima's four major eruptions since 1869, spanning the last two eruptive cycles. Colima's post-caldera andesites are poor in K and other incompatible elements (Ti,P, Zn, Rb, Y, Zr, Ba, La, Yb, Hf, Th, and U) as may be characteristic of near trench andesites. From the 1913 ashflow eruption through the fourth cycle andesites, there have been increases in whole rock abundances of Si, Ba, and Cs, and decreases in Ti, Fe, Mg, Ni, Cr, and Sc. Crystal fractionation models can closely reproduce major element variations in the post-caldera suite, but systematically fail to predict sufficient concentrations of the compatible trace elements Cr, Ni, and Zn. Anomalous enrichments of compatible trace elements in Colima's andesites probably reflect simultaneous crystal fractionation and magma mixing in the subvolcanic system.Estimated pre-eruptive temperatures range from 940 °–1,000 ° C in the hornblende-andesites and 1,030 °–1,060 ° C in the olivine-andesites. Pre-eruptive magmatic water contents of 1.0–3.6 wt.% are calculated for the hornblende-andesites; the phenocryst assemblage of the olivine-andesite is calculated to equilibrate at 1,000 bars with 0.8% H2O.Orthopyroxenes and certain clinopyroxenes in all pre-1961 samples are reversely zoned, with relatively Mg-rich rims. The most pronounced Mg-rich rims occur in the olivine-andesites and are thought to reflect pre-eruptive magma mixing, involving a basic, olivine+/-clinopyroxene-bearing magma. In addition to their normally zoned pyroxenes, the post-1961, fourth cycle andesites display a number of other features which distinguish them from earlier post-caldera hornblende-andesites of similar bulk composition. These include: (1) higher total crystal contents, (2) lower modal hornblende contents, (3) higher calculated pre-eruptive silica activities, and (4) lower calculated pre-eruptive water contents. These features are all consistent with the interpretation that the fourth cycle andesites were less hydrous prior to eruption. The slight Mg-rich pyroxene rims in pre-1961 hornblende-andesites may record late-stage, pre-eruptive increases in magmatic water content, which act to raise magmaticfO2and Mg/Fe+2ratios in the melt and in all crystalline phases. The fourth cycle andesites apparently did not experience a strong, pre-eruptive influx of water, resulting in lower magmatic water contents and normally zoned pyroxenes.