Magmatic history of Dabbahu, a composite volcano in the Afar Rift, Ethiopia
Magmatic history of Dabbahu, a composite volcano in the Afar Rift, Ethiopia
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DOI：
10.1130/b30560.1
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发表时间：
2013
影响因子：
4.9
通讯作者：
L. Field;J. Blundy;A. Calvert;G. Yirgu
中科院分区：
文献类型：
--
作者：
L. Field;J. Blundy;A. Calvert;G. Yirgu
达巴胡火山是埃塞俄比亚北方阿法尔裂谷活跃的曼达-哈拉罗段北端的一座复合火山。我们提出了93个新的全岩分析，矿物分析65个样品，9个新的40 Ar 39 Ar年龄的岩石组成范围从温和的碱性玄武岩通过粗安岩过碱性流纹岩（comendite和pantellerite）爆发Dabbahu。这些数据加上新的地质图，可用于深入了解火山的演变。我们发现达巴胡已经活跃了超过67千年，但在comendite（29 ka）和pantellerite（约10 ka）的喷发之间存在明显的间断。8 ka）熔岩。橄榄石，单斜辉石，斜长石和碱性长石的矿物数据显示了一个显着广泛的范围内的固溶体在整个岩石套件一致的长期分馏从玄武岩到流纹岩。母玄武岩的成分类似于Manda-Hararo裂谷中与裂谷有关的玄武岩，初始H2O含量较低（<1重量%）。封闭系统分馏增加了残余液体的H2O含量，足以使一些流纹岩爆发性和溢出性。不同类型的岩浆是从一个相对密集的喷口和裂缝网络中喷发出来的。现场证据表明，岩浆喷发不是在一个简单的分馏序列。一些混合之间发生的岩浆少进化的组合物和更进化的组合物之前不久，或在喷发过程中。玄武岩到流纹岩的分异一定发生在与火山寿命相比相对较短的时间尺度上，这可能是由于侵入地壳的玄武岩体积较小，从而提高了冷却和结晶速率。在地壳浅部至中部的堆积岩床或紧密间隔的岩脉网络代表了次火山管道系统最合理的配置。新的岩浆批次输入到这样一个系统中可能是Dabbahu火山爆发的关键触发因素。
Dabbahu is a composite volcano at the north end of the active Manda-Hararo segment of the Afar Rift in northern Ethiopia. We present 93 new whole-rock analyses, mineral analyses from 65 samples, and 9 new 40Ar39Ar dates for rocks ranging in composition from mildly alkaline basalt through trachyandesite to peralkaline rhyolite (comendite and pantellerite) erupted from Dabbahu. These data, supplemented by a new geological map, are used to provide insights into the evolution of the volcano. We show that Dabbahu has been active for over 67 k.y., but an apparent hiatus occurred between the eruption of comendite (29 ka) and pantellerite (ca. 8 ka) lavas. Mineral data for olivine, clinopyroxene, plagioclase, and alkali feldspar show a remarkably extensive range of solid solution across the rock suite consistent with protracted fractionation from basalt to rhyolite. The parental basalt is compositionally similar to recent rift-related basalts in the Manda-Hararo rift, with low initial H2O contents (<1 wt%). Closed-system fractionation increased H2O contents of residual liquids sufficiently for some rhyolites to erupt both explosively and effusively. The diverse magma types were erupted from a relatively closely spaced network of vents and fissures. Field evidence indicates that magmas were not erupted in a simple fractionation sequence. Some mixing occurred between magmas of less-evolved compositions and more-evolved compositions shortly prior to, or during, eruption. The differentiation of basalt to rhyolite must have occurred on time scales that were relatively short compared to the lifetime of the volcano, probably due to the small volumes of basalt intruded into the crust and consequently enhanced cooling and crystallization rates. A network of stacked sills or closely spaced dikes in the shallow to midcrust represents the most plausible configuration of the subvolcanic plumbing system. Input of new magma batches into such a system may serve as a key eruption trigger at Dabbahu.