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首页> 外文期刊>Journal of Volcanology and Geothermal Research >Reconstruction of the Sibinal Pumice, an andesitic Plinian eruption at Tacana Volcanic Complex, Mexico-Guatemala
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Reconstruction of the Sibinal Pumice, an andesitic Plinian eruption at Tacana Volcanic Complex, Mexico-Guatemala

机译：墨西哥-危地马拉塔卡纳火山综合体的安第斯山普林斯喷发的锡比纳浮石的重建

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The Tacana Volcanic Complex, located on the Mexico-Guatemala border, has had numerous small historical explosions, the latest being a phreatic explosion in 1986. The stratigraphic record, however, suggests that much more voluminous eruptions have occurred in the past. Here, we document one such eruption, the Sibinal Pumice deposit, which occurred ca. 23,540 years B.P. The deposit consists of two pumice-rich units: 1) a lower stratified member (SM) that consists of at least seven, normally graded fall layers, interbedded with pyroclastic wet surge layers; and 2) an upper massive member (MM), made up of a single fall deposit. Both members can reach up to 2.5 m in thickness and are separated by a single massive, indurated, yellowish, pumice-rich reworked layer. SM was dispersed to the northeast (N70°E), with its 6-cm isopach covering an area of 275 km~2, whereas MM was dispersed to the north (N22°E), with its 70-cm isopach covering an area of ca. 330 km~2. Yellow, vesicular pumice fragments, light-gray lithics, and hydrothermally altered (red and black) dense lithics are abundant in both members, although altered lithics are more abundant at the base of each, reaching 15 vol.%. Pumice compositions range from basaltic to andesitic (48-61 wt.% SiO_2, anhydrous basis), but are highly altered. They contain plagioclase (andesine-labradorite), augite, hypersthene, Fe-Ti oxides, and rare amphibole. No compositional or mineralogical differences occur between the units indicating a common magma source during the same eruption. The Sibinal Pumice eruption started with a weak, pulsating column that reached at most 19 km in height, ejecting 2.9 km3 of tephra (1.1 km~3 DRE) at an average mass discharge rate of 4.7 ×10~7 kg/s, with repeated hydromagmatic explosions that generated wet surges down the slopes of the volcano. The eruption ceased for a while during which rainfall generated a widespread lahar that eroded the top of SM. The eruption began anew with a sustained and stable Plinian column that ejected 4.6 km~3 (1.9 km~3 DRE) of tephra at a mass discharge rate of 8.1 × 10~7 kg/s. The lack of any compositional differences in the magma suggests that the change in eruptive style was driven by influxes of external water provoking hydromagmatic explosions that cleared the conduit, then, the system changed to dry system and the eruption style changed from pulsating to stable Plinian. As the conduit became wider, the mass discharge rate also increased.
机译：位于墨西哥-危地马拉边界的塔卡纳火山综合体曾发生过多次小规模的历史性爆炸，最近一次是在1986年发生的一次水下爆炸。但是，地层记录表明，过去发生了更多的大规模喷发。在这里，我们记录了一次这样的喷发，锡比纳尔浮岩矿床，发生于约。公元前23,540年该矿床由两个富含浮石的单元组成：1）下分层成员（SM），该成员至少由七个通常为梯度的降层组成，并与火山碎屑湿浪涌层夹层； 2）上部大型成员（MM），由单个秋季沉积物组成。两个部件的厚度均可以达到2.5 m，并由单个块状，坚硬，淡黄色，浮石重工的返工层隔开。 SM分散到东北（N70°E），其6厘米等值线覆盖面积275 km〜2，而MM分散到北部（N22°E），其70厘米等值线覆盖范围为ca. 330公里〜2。黄色，囊状浮石碎片，浅灰色石板和水热蚀变的（红色和黑色）致密石板在这两个构件中均富集，尽管蚀变的石板在每个底部都更为丰富，达到15％（体积）。浮石的组成范围从玄武岩到安山岩（48-61 wt。％SiO_2，无水），但变化很大。它们包含斜长石（长石碱-拉长石），辉石，高硫醚，铁钛氧化物和稀有的闪石。在同一喷发过程中，这两个单元之间没有组成或矿物学上的差异，这表明它们是一个共同的岩浆源。锡比纳河浮石喷发始于一个弱的脉动柱，柱高不超过19 km，以4.7×10〜7 kg / s的平均质量排放速率喷出2.9 km3的提菲拉（1.1 km〜3 DRE）。沿火山坡向下产生潮涌的水力岩爆。喷发停止了一段时间，在此期间降雨产生了广泛的拉哈，侵蚀了SM的顶部。喷发重新开始，持续而稳定的Plinian柱以8.1×10〜7 kg / s的质量排放速率喷出4.6 km〜3（1.9 km〜3 DRE）的邻苯二酚。岩浆中没有任何成分差异，表明喷发方式的变化是由外部水的涌入引起的，导致激流的岩浆爆炸清除了管道，然后，系统变为干系统，喷发方式由脉动变为稳定的普利尼安。随着导管变宽，质量排放率也增加。

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