The 1996 eruption of Karymsky volcano, Kamchatka: Historical record of basaltic replenishment of an andesite reservoir
The 1996 eruption of Karymsky volcano, Kamchatka: Historical record of basaltic replenishment of an andesite reservoir
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DOI：
10.1093/petrology/egh059
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发表时间：
2004-11-01
影响因子：
3.9
通讯作者：
Ivanov, BV
中科院分区：
文献类型：
--
作者：
Izbekov, PE;Eichelberger, JC;Ivanov, BV
1996年，卡里姆斯基火山的安山岩和6公里外诺克学院喷口的玄武岩同时喷发，似乎提供了一个安山岩储集层的镁铁质补给案例，其补给时间是确切的，而且可以获得补给岩浆的直接样品。玄武岩的爆发性潜浆喷发在不到24小时内终止，而安山岩在随后的4年中持续喷发。对1996-1999年期间喷发的卡里姆斯基安山岩的火山灰、火山弹和熔岩进行了详细的岩石学研究，为玄武岩循环开始时的玄武岩补给提供了证据，并记录了玄武岩补给导致卡里姆斯基岩浆储集层内的成分变化。喷发开始后不久，卡里姆斯基火山的基质玻璃的成分变得更加镁铁质，然后在2个月内逐渐恢复到原来的状态，并在接下来的3年里几乎保持不变。在卡里姆斯基的安山岩中存在玄武岩成因的捕虏晶，为玄武岩的补充提供了进一步的证据。卡里姆斯基安山岩中斜长石斑晶的明显部分具有钙核，其成分和结构类似于Academy Nauk玄武岩中的斜长石。同样，喷发序列的安山岩的早期部分含有稀有的橄榄石，它们作为重新吸收的岩芯出现在辉石中。橄榄石的成分与诺克学院玄武岩中的橄榄石相匹配。事件的顺序似乎是：(1)玄武岩岩浆注入卡里姆斯基洞穴，同时从卡里姆斯基中央喷口立即补偿地排出先前存在的洞室岩浆；(2)玄武岩和安山质岩浆直接混合，与玄武岩有关的斑晶在安山岩中扩散，从而在2个月内在喷口出现新的混合岩浆；(3)在新的混合液体中重新建立热和化学平衡，使熔体成分恢复到正常，在继承的钙斜长石上形成边缘，并导致分散的橄榄石捕虏晶被吸收。综上所述，这些发现表明，1996年喷发旋回开始时，卡里姆斯基岩浆储集层受到玄武岩的补给。玄武岩与先前存在的安山岩混合的迅速和彻底可能反映了两个岩浆在温度、粘度和密度方面的适度对比。
The simultaneous eruption in 1996 of andesite from Karymsky volcano and of basalt from the Academy Nauk vent 6 km away appears to provide a case of mafic recharge of an andesite reservoir for which the time of recharge is exactly known and direct samples of the recharging magma are available. The explosive phreato-magmatic eruption of basalt was terminated in less than 24 h, whereas andesite erupted continuously during the following 4 years. Detailed petrological study of volcanic ash, bombs and lavas of Karymsky andesite erupted during the period 1996-1999 provides evidence for basaltic replenishment at the beginning of the eruptive cycle, as well as a record of compositional variations within the Karymsky magma reservoir induced by basaltic recharge. Shortly after the beginning of the eruption the composition of the matrix glass of the Karymsky tephra became more mafic and then, within 2 months, gradually returned to its original state and remained almost constant for the following 3 years. Further evidence for basaltic replenishment is provided by the presence of xenocrysts of basaltic origin in the andesite of Karymsky. A conspicuous portion of the plagioclase phenocrysts in the Karymsky andesite has calcic cores, with compositions and textures resembling those of plagioclases in the Academy Nauk basalt. Similarly, the earlier portion of the andesite of the eruption sequence contains rare olivines, which occur as resorbed cores in pyroxenes. The composition of the olivine matches that of olivines in the Academy Nauk basalt. The sequence of events appears to be: (1) injection of basaltic magma into the Karymsky chamber with immediate, compensating expulsion of pre-existing chamber magma from the Karymsky central vent; (2) direct mixing of basaltic and andesitic magmas with dispersal of phenocrysts associated with the basalt throughout the andesite so that newly mixed magma appeared at the vent within 2 months; (3) re-establishment of thermal and chemical equilibrium within the reservoir involving crystallization in the new hybrid liquid, which returned the melt composition to 'normal', formed rims on inherited calcic plagioclase, and caused the resorption of dispersed olivine xenocrysts. Taken together, these findings indicate that the Karymsky magma reservoir was recharged by basalt at the onset of the 1996 eruptive cycle. The rapidity and thoroughness of mixing of the basalt with the pre-existing andesite probably reflects the modest contrast in temperature, viscosity, and density between the two magmas.