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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Insights into shallow magma storage and crystallization at Volcán Llaima(Andean Southern Volcanic Zone, Chile)
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Insights into shallow magma storage and crystallization at Volcán Llaima(Andean Southern Volcanic Zone, Chile)

机译：VolcánLlaima（智利安第斯南部火山带）浅层岩浆储存和结晶的见解

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摘要

Scoriae produced by four mafic historic eruptions of Volcán Llaima are used to elucidate magma differentiation, recharge, mixing, and eruption triggering. Whole-rock, mineral, and olivine-hosted melt inclusion chemistry suggest that basaltic andesites (-52-53.5 wt.% SiO_2) stall at immediately sub-edifice depths (≦4 km beneath the base of the volcano), where they crystallize to large extents and form mush bodies. Melt inclusion trends overlap with the whole-rock data trends defined by the entire volcano up to 53-55% SiO_2, but more evolved compositions define divergent trends for some elements, with up to 2.2 wt% TiO_2 (increasing Zr) and A1_2O_3 as low as 12.5 wt% (decreasing Sr) at 57-58 wt.% SiO_2. These more evolved melt compositions are inferred to be the result of shallow evolution of interstitial melt during the formation of crystal mush bodies, as a consequence of degassing and crystallization with a reduced participation of Fe-Ti-oxides. The inferred suppression of Fe-Ti-oxide stability and the modal dominance of plagioclase crystallization are consistent with low fluid-saturation pressures of -40-70 MPa inferred from average H_2O contents for mafic arc magmas (dominantly 1-4 wt.%) but low CO_2 contents (dominantly 0-300 ppm) in melt inclusions. The broad range in olivine core compositions (Fo_(59-83)) and the absence of correlated degassing and magma evolution trends in historic Llaima magmas suggest that they are stored as multiple dike-like bodies created by a high frequency of magma replenishment relative to the frequency of large eruptions. This temporal-spatial disconnection leads to isolated evolution and degassing of discrete magma batches, followed by remobilization and assembly just prior to eruption. Eruptions are probably triggered by recharge of relatively hot, mafic, and much less degassed magma, in accord with dominantly reversely-zoned olivine crystals, and higher olivine-melt temperatures recorded by the relatively primitive matrix glasses and coexisting olivine rims.
机译：VolcánLlaima的四个基性历史喷发产生的孢子虫被用于阐明岩浆分化，补给，混合和喷发触发。全岩石，矿物和橄榄石包裹的熔体夹杂化学表明，玄武质安山岩（-52-53.5 wt。％SiO_2）停在紧邻地下的深度（火山底部以下≤4 km），在那里结晶成在很大程度上形成糊状体。熔体夹杂物趋势与整个火山所定义的全岩石数据趋势重叠，最高可达53-55％SiO_2，但更多演化的成分定义了某些元素的趋异趋势，其中最高为2.2 wt％的TiO_2（Zr增大）和A1_2O_3低SiO_2在57-58wt。％时为12.5wt％（降低的Sr）。可以认为，这些析出的熔体成分更多是由于在结晶糊状体形成过程中间隙熔体浅析出的结果，这是脱气和结晶的结果，Fe-Ti-氧化物的参与减少。从铁镁弧岩浆的平均H_2O含量（主要为1-4 wt。％）推断出的Fe-Ti-氧化物稳定性抑制和斜长石结晶的模态优势与-40-70 MPa的低流体饱和压力相一致，但是熔融夹杂物中的CO_2含量低（主要为0-300 ppm）。橄榄岩核心成分范围广泛（Fo_（59-83）），并且在历史悠久的莱马岩浆中没有相关的脱气和岩浆演化趋势，这表明它们被存储为多个堤防状体，是由相对于岩浆补给频率较高而产生的。大爆发的频率。这种时空的分离导致离散的岩浆批次的分离演化和脱气，然后在喷发之前进行重新固定和组装。火山喷发可能是由相对热的，镁铁质且脱气的岩浆充填引起的，这与主要逆带化的橄榄石晶体相一致，以及相对原始的基质玻璃和共存的橄榄石边缘记录的更高的橄榄石融解温度。

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  • 来源
    《Journal of Volcanology and Geothermal Research》 |2012年第15期|p.76-91|共16页
  • 作者

    C. Bouvet de Maisonneuve; MA Dungan; O. Bachmann; A. Burgisser;

  • 作者单位

    University of Geneva, Earth and Environmental Sciences Section, 13 rue des Maraichers, 1205 Geneva, Switzerland;

    University of Geneva, Earth and Environmental Sciences Section, 13 rue des Maraichers, 1205 Geneva, Switzerland;

    University of Washington, Earth and Space Sciences, Seattle, WA 98195-1310, USA;

    ISTO, CNRS-University of Orleans, 45071 Orleans, France;

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