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首页> 外文期刊>Contributions to Mineralogy and Petrology >Petrological imaging of an active pluton beneath Cerro Uturuncu, Bolivia
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Petrological imaging of an active pluton beneath Cerro Uturuncu, Bolivia

机译：玻利维亚Cerro Uturuncu下的活动岩体的岩石学成像

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Uturuncu is a dormant volcano in the Altiplano of SW Bolivia. A present day ~70 km diameter interferometric synthetic aperture radar (InSAR) anomaly roughly centred on Uturuncu's edifice is believed to be a result of magma intrusion into an active crustal pluton. Past activity at the volcano, spanning 0.89 to 0.27 Ma, is exclusively effusive and almost all lavas and domes are dacitic with phenocrysts of plagioclase, orthopyroxene, biotite, ilmenite and Ti-magnetite plus or minus quartz, and microlites of plagioclase and orthopyroxene set in rhyolitic groundmass glass. Plagioclase-hosted melt inclusions (MI) are rhyolitic with major element compositions that are similar to groundmass glasses. H_2O concentrations plotted versus incompatible elements for individual samples describe a trend typical of near-isobaric, volatile-saturated crystallisation. At 870 °C, the average magma temperature calculated from Fe-Ti oxides, the average H_2O of 3.2 ± 0.7 wt% and CO_2 typically <160 ppm equate to MI trapping pressures of 50-120 MPa, approximately 2-4.5 km below surface. Such shallow storage precludes the role of dacite magma emplacement into preemptive storage regions as being the cause of the observed InSAR anomaly. Storage pressures, whole-rock (WR) chemistry and phase assemblage are remarkably consistent across the eruptive history of the volcano, although magmatic temperatures calculated from Fe-Ti -oxide geothermometry, zircon saturation thermometry using MI and orthopyroxene-melt thermometry range from 760 to 925 ℃ at NNO ± 1 log. This large temperature range is similar to that of saturation temperatures of observed phases in experimental data on Uturuncu dacites. The variation in calculated temperatures is attributed to piecemeal construction of the active pluton by successive inputs of new magma into a growing volume of plutonic mush.
机译：乌图伦库（Uturuncu）是西南玻利维亚高原的一座休眠火山。如今，大约70 km直径的干涉合成孔径雷达（InSAR）异常大致集中在Uturuncu的建筑物中心，据认为是岩浆侵入活动地壳的结果。火山的过去活动范围为0.89至0.27 Ma，仅是喷发性的，几乎所有的熔岩和穹顶都是斜长石，邻辉石，黑云母，钛铁矿和钛磁铁矿的正石英，正负石英，以及斜长石和邻辉石的微晶岩。流纹地面玻璃。斜长石为基质的熔体夹杂物（MI）是流纹岩，其主要元素组成与地面玻璃相似。绘制的H_2O浓度与单个样品中不相容元素的关系描述了接近等压，挥发性饱和结晶的典型趋势。在870°C下，由Fe-Ti氧化物计算出的平均岩浆温度，平均H_2O为3.2±0.7 wt％，CO_2通常<160 ppm，相当于50-120 MPa的MI捕集压力，大约在地表以下2-4.5 km。这种浅层存储排除了将达菲特岩浆放入先发性存储区的作用，这是观察到的InSAR异常的原因。尽管从铁钛氧化物地热法计算的岩浆温度，使用MI的锆石饱和测温法和邻二甲苯熔体测温法测得的岩浆温度范围为760到760，但整个火山的爆发历史上的储藏压力，全岩（WR）化学和相组合都非常一致。 NNO±1 log时为925℃。这个较大的温度范围类似于乌图伦库（Uturuncu dacites）的实验数据中观察到的相的饱和温度。计算温度的变化归因于新岩浆连续输入不断增长的深成一体的岩浆中的活动岩体的零星构造。

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