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首页> 外文期刊>Journal of Volcanology and Geothermal Research2012V243-244NOCT,15 >Highly explosive 2010 Merapi eruption: Evidence for shallow-level crustal assimilation and hybrid fluid
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Highly explosive 2010 Merapi eruption: Evidence for shallow-level crustal assimilation and hybrid fluid

机译：高度爆炸性的2010年默拉皮火山喷发：浅层地壳同化和混合流体的证据

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摘要

The processes responsible for the highly explosive events at Merapi, Central Java, Indonesia have been investigated through a petrological, mineralogical and geochemical study of the first-stage tephra and pyroclastic flows sampled in October and November 2010, and second-stage ash sampled shortly after the 5-6th November 2010 paroxysmal subplinian eruption. Several chemical and physical parameters suggest that the magma assimilated calc-silicate xenoliths derived from the surrounding carbonate-bearing crust (Javanese limestone). The bulk volcanic samples have highly radiogenic ~(87)Sr/~(86)Sr (0.70571-0.70598) ratios that approach the compositional field of material similar to the calc-silicate xenoliths. The 2010 plagioclase phenocrysts from the pyroclastic flow and tephra reveal anorthite cores (up to An_(94-97)) with low FeO contents (≤0.8 wt.%), and ~(18)O enrichment (6.5‰ δ~(18)O). The major and trace elements of the silicic glasses and phenocrysts (plagioclase, low-Al augite and titanomagnetite), the Sr-isotopic compositions of the bulk samples and plagioclases erupted in 2010 can be explained by complete digestion of the 1998 and 2006 calc-silicate xenoliths. The bulk assimilation proceeded through binary mixing between a calcic melt (representing Crustal Assimilant, CaO up to 10.5 wt% and CaO/ A1_2O_3 up to 1.2) and the deep source hydrous K-rich melt Similarly to the 1998 and 2006 calc-silicate xenolith composition, the 2010 Crustal Assimilant is enriched in Mn (MnO up to 0.5 wt%), Zn, V, and Sc contents. In contrast, the hydrous K-rich melt is enriched in volatiles (Cl up to 0.37 wt% and bulk H_2O ± CO_2 up to 5 ± 1 wt.%), Al_2O_3, TiO_2 and REE contents, consistent with its derivation from deep source. This hydrous K-rich melt may have been saturated with an aqueous Cl-rich fluid at about 200 MPa, a pressure consistent with the level of the crustal assimilation. We estimated that the pre-eruptive basaltic andesite magma assimilated from 15 to 40 wt.% of the calc-silicate crustal material, corresponding to introduction of additional 0.19 to 2.1 Mt of CO_2 to the magma. Experimental leaching of the ash samples documents the release of an aqueous fluid enriched in Cl, Na, Ca, Cd, Sb and Zn during the paroxysmal subplinian eruption. The paroxysmal eruption may have been produced by saturation of the pre-eruptive basaltic andesite magma with hybrid aqueous carbonic NaCl-HCl-rich fluid due to bulk assimilation creating elevated partial pressure of CO_2 at shallow crustal conditions of about 200 MPa. In contrast, mildly explosive block-and-ash flows (typical Merapi-type) may result from selective assimilation of the carbonate-bearing xenoliths and lower CO_2 partial pressure that may not lead to explosive degassing.
机译：通过岩石，矿物学和地球化学研究，调查了2010年10月和11月采样的第一阶段的特弗拉和火山碎屑流以及第二阶段的灰分之后对岩石进行采样的岩石学，矿物学和地球化学研究，调查了造成印度尼西亚中爪哇省默拉皮市高度爆炸事件的过程。 2010年11月5日至6日阵发性亚临床发作。几个化学和物理参数表明，岩浆吸收了周围含碳酸盐的地壳（爪哇石灰岩）中的钙硅酸盐异岩。大块火山岩样品具有高放射源性〜（87）Sr /〜（86）Sr（0.70571-0.70598）比，接近与钙硅酸盐异种岩相似的材料组成区域。来自2010年的火山碎屑流和特非拉的斜长石斜角晶岩显示出钙长石岩心（高达An_（94-97））具有低FeO含量（≤0.8wt。％）和〜（18）O富集（6.5‰δ〜（18）） O）。硅酸盐玻璃和隐晶石的主要和微量元素（斜长石，低铝辉石和钛磁铁矿），2010年爆发的大块样品和斜长石的Sr同位素组成可以通过1998年和2006年的钙硅酸盐的完全消化来解释。异石。大量同化是通过在钙熔体（代表地壳同化体，CaO高达10.5 wt％，CaO / A1_2O_3高达1.2）与深水源富含钾的熔体之间进行二元混合而进行的，类似于1998和2006 ，2010年的地壳同化物富含Mn（MnO含量最高为0.5 wt％），Zn，V和Sc含量。相比之下，含水的富含K的熔体富含挥发物（Cl含量高达0.37 wt％，而H_2O±CO_2含量高达5±1 wt。％），Al_2O_3，TiO_2和REE含量，这与它源自深源的结果一致。该含水的富含钾的熔体可能已经在约200 MPa的压力下与地壳同化水平相一致，被富含Cl的含水流体所饱和。我们估计喷发前的玄武质安山岩岩浆吸收了15％至40 wt％的钙硅酸盐地壳物质，相当于向岩浆中引入了额外的0.19至2.1 Mt的CO_2。灰分样品的实验浸出表明在阵发性亚p爆发期间释放了富含Cl，Na，Ca，Cd，Sb和Zn的水性流体。阵发性喷发可能是由于喷发前的玄武质安山岩岩浆与富含NaCl-HCl的混合含水碳氢化合物流体饱和而引起的，这是由于大量同化作用在约200 MPa的浅地壳条件下产生了升高的CO_2分压所致。相反，轻度爆炸性的块状和灰分流（典型的Merapi型）可能是由于含碳酸盐异岩的选择性同化和较低的CO_2分压而产生的，而这可能不会导致爆炸性脱气。

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