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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Evolution and hydrological conditions of a maar volcano (Atexcac crater, Eastern Mexico)
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Evolution and hydrological conditions of a maar volcano (Atexcac crater, Eastern Mexico)

机译：玛尔火山的演化和水文条件（东墨西哥阿特克斯卡火山口）

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The Atexcac maar is located in the central part of the Serdan-Oriental lacustrine/playa basin in the eastern Mexican Volcanic Belt. It is part of a dispersed and isolated monogenetic field consisting of maar volcanoes, basaltic cinder cones and rhyolitic domes. Atexac is a maar volcano excavated into pyroclastic deposits, basaltic lava flows and the flanks of a cinder cone cluster, which itself was built on a topographic high consisting of limestone. It has an ENE-trending elliptical shape with beds, mostly unconsolidated deposits that dip outward at 16-22°. The Atexcac crater was formed from vigorous phreatomagmatic explosions in which fluctuations in the availability of external water, temporal migration of the locus of the explosion, and periodic injection of new magma were important controls on the evolution of the maar crater. Variations in grain sizes and component proportions of correlated deposits from the different sections suggest a migration of the locus of explosions, producing different eruptive conditions with fluctuating water-magma interactions. Deposits rich in large intrusive and limestone blocks are associated with a matrix enriched in small andesitic lapilli. This could suggest differential degrees of fragmentation due to inherited (previously acquired) fragmentation and/or relative distance to the locus of explosions. Initial short-lived phreatic explosions started at the southwest part of the crater and were followed by an ephemeral vertical column and the influx of external water that led to relatively shallow explosive interactions with the ascending basaltic magma. Drier explosions progressed downward and/or laterally northward, sampling subsurface rock types, particularly intrusive, limestone and andesitic zones as well as localized altered zones (N-NE), caused by repetitive injection of basaltic magma. A final explosive phase involved a new injection of magma and a new influx of external water producing wetter conditions at the end of the maar formation. We infer the aquifer was formed by fractured rocks, predominantly andesitic lava flows and limestone rocks. Andesitic accessory clasts dominate in all stratigraphic levels but these rocks are not exposed in the nearby area. These local hydrogeological conditions contrast with those at nearby maar volcanoes, where the water for the magma/water interactions apparently mostly came from a dominantly unconsolidated tuffaceous aquifer, producing tuff rings with a much lower profile than Atexcac.
机译：Atexcac岩浆位于墨西哥东部火山带Serdan-Oriental湖泊/普拉亚盆地的中部。它是由玛尔火山，玄武质煤渣锥和流纹岩穹顶组成的分散和孤立的单基因场的一部分。阿特塔克火山是一个玛尔火山，被开挖成火山碎屑沉积，玄武岩熔岩流和煤渣锥团簇的侧面，而煤渣锥团簇本身是建立在由石灰石组成的地形高处。它呈ENE趋势的椭圆形，带有床，大部分为未固结的沉积物，向16-22°处向外倾斜。 Atexcac火山口是由剧烈的岩浆爆炸形成的，其中外部水的供应量波动，爆炸地点的时间迁移以及新的岩浆的定期注入是玛氏火山口演变的重要控制因素。来自不同区域的相关沉积物的晶粒尺寸和成分比例的变化表明爆炸的轨迹发生了迁移，从而产生了具有波动的水岩浆相互作用的不同喷发条件。富含大量侵入岩和石灰岩块体的沉积物与富含小型安第斯山脉洛皮绒的基质有关。这可能表明由于继承的（先前获得的）碎片和/或距爆炸地点的相对距离而导致的碎片程度不同。最初的短期潜水爆炸始于火山口的西南部，随后是短暂的垂直柱和外部水的涌入，导致与上升的玄武岩浆的爆炸作用较浅。较干燥的爆炸向下和/或横向向北发展，对地下岩浆进行了采样，特别是侵入岩，石灰岩和安山岩带以及局部蚀变带（N-NE），这是由于玄武岩浆的重复注入引起的。最后的爆炸阶段涉及在岩浆形成的末期注入新的岩浆并注入新的外部水，从而产生较湿的条件。我们推断含水层是由破裂的岩石，主要是安第斯山脉的熔岩流和石灰岩构成的。安第斯山脉附件碎屑在所有地层中均占主导地位，但这些岩石在附近区域未暴露。这些当地的水文地质条件与附近的玛尔火山形成鲜明对比，那里的岩浆/水相互作用水显然主要来自未固结的凝灰质含水层，产生的凝灰岩环比阿特斯卡克低得多。

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