Magma storage conditions beneath Dabbahu Volcano (Ethiopia) constrained by petrology, seismicity and satellite geodesy
Magma storage conditions beneath Dabbahu Volcano (Ethiopia) constrained by petrology, seismicity and satellite geodesy
复制标题
DOI：
10.1007/s00445-012-0580-6
复制
发表时间：
2012-07-01
影响因子：
3.5
通讯作者：
Yirgu, G.
中科院分区：
文献类型：
--
作者：
Field, L.;Blundy, J.;Yirgu, G.
存在多种方法来限制岩浆的次火山储存条件。综合岩石学、地震学和卫星大地测量方法，确定埃塞俄比亚阿法尔达巴胡火山下过碱性岩浆的储存条件。二次离子质谱（西姆斯）分析了最年轻喷发阶段（< 8 ka）的碱碲黑曜岩中碱性长石、单斜辉石和橄榄石斑晶中的熔融包裹体中的挥发分含量，结果表明H2O含量为千分之5.8wt.% CO2含量一般低于500 ppm，但很少高达1,500 ppm。挥发分饱和压力（在679- 835 A摄氏度）在43-207 MPa的范围内，与已发表的类似的碱碲矿的实验数据一致，其显示碱性长石+ cpx +霓霞岩+/-钛铁矿的斑晶组合在100 - 150 MPa是稳定的。推断这些历史性喷发的岩浆储存深度类似于海平面以下1-5公里，与地震的深度一致，与2005年10月至2006年4月期间堤坝侵入后的岩浆房通缩有关。同一时期的干涉合成孔径雷达（干涉合成孔径雷达）数据显示，有一个直径约为20公里的广阔隆起区。对不同几何形状的建模表明，一系列1-5公里深度范围内的叠置岩床与干涉合成孔径雷达数据最匹配。根据对古代喷发的岩石学研究和2005年堤坝事件中观察到的Dabbahu的地震活动、通货膨胀和通货紧缩，深度估计的一致性表明，存在一个规模小但垂直方向广泛、寿命可能较长的岩浆储存区。
A variety of methods exist to constrain sub-volcanic storage conditions of magmas. Petrological, seismological and satellite geodetic methods are integrated to determine storage conditions of peralkaline magmas beneath Dabbahu Volcano, Afar, Ethiopia. Secondary ion mass spectrometry (SIMS) analysis of volatile contents in melt inclusions trapped within phenocrysts of alkali feldspar, clinopyroxene and olivine from pantellerite obsidians representing the youngest eruptive phase (< 8 ka) show H2O contents a parts per thousand currency sign5.8 wt.% and CO2 contents generally below 500 ppm, although rarely as high as 1,500 ppm. Volatile saturation pressures (at 679-835A degrees C) are in the range 43-207 MPa, consistent with published experimental data for similar pantellerites, which show that the phenocryst assemblage of alkali feldspar + cpx + aenigmatite +/- ilmenite is stable at 100 to 150 MPa. Inferred magma storage depths for these historic eruptions are similar to 1-5 km below sea-level, consistent with the depths of earthquakes, associated with magma chamber deflation following a dyke intrusion in the period Oct 2005-Apr 2006. Interferometric synthetic aperture radar (InSAR) data for the same period reveal a broad similar to 20 km diameter area of uplift. Modelling of different geometries reveals that a series of stacked sills over a 1-5 km depth range best matches the InSAR data. The consistency of depth estimates based on petrological study of ancient eruptions and the seismicity, inflation and deflation of Dabbahu observed in relation to the dyking event of 2005, suggest a small but vertically extensive and potentially long-lived magma storage region.