Millennial to decadal magma evolution in an arc volcano from zircon and tephra of the 2016 Santiaguito eruption (Guatemala)
Millennial to decadal magma evolution in an arc volcano from zircon and tephra of the 2016 Santiaguito eruption (Guatemala)
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2016 年圣蒂亚吉托火山喷发（危地马拉）的锆石和火山灰在弧火山中的千年至十年岩浆演化
DOI：
10.1016/j.lithos.2019.04.027
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发表时间：
2016
期刊：
影响因子：
3.5
通讯作者：
Juárez
中科院分区：
文献类型：
--
作者：
Cisneros de León;Schmitt;Schindlbeck-Belo;Trumbull;Juárez
圣玛丽亚-圣地亚吉托火山综合体是整个中美洲火山弧中最活跃、最危险的火山之一。1902年，圣玛丽亚平流层锥(危地马拉)发生破坏性的普林尼亚喷发，在20 年内，圣地亚吉托火山穹顶建筑群开始由寄生喷口喷发形成，持续了近一个多世纪。由于圣地亚吉托火山的频繁喷发，它为以高时间分辨率研究其次火山岩浆储集层的长期变化提供了独特的机会。2016年8月，在圣地亚吉托喷发后的几天和几个小时内，在一段异常爆炸性的时间段内收集的火山灰代表了一些演化程度最低的成分(60%-62%的二氧化硅)，该系统的87Sr/86Sr同位素比率是有史以来报道过的最低的。这将圣地亚吉托的数十年趋势延伸到随着时间的推移，岩浆成分随时间演变得越来越少，相对于1902年喷发了绝大多数英安质浮岩的事件。Santiaguito的地球化学变化表明，1902年喷发后残留的新鲜玄武岩安山岩岩浆与英安岩浆混合而成的贡献越来越大。高分辨率二次离子质谱仪(SIMS)238U-230Te不平衡测年和来自Santiaguito火山灰和Santa María 1902浮石的锆石地球化学研究表明，在构成Santa María中心锥体的整个约100 KYR玄武岩安山岩喷发区间内，存在演化的和锆石饱和的熔体。在Santa María 1902矿床中常见石英闪长岩基底包体(~55%SiO_2)和始新世锆石，在Santiaguito火山灰中有少量同样古老的锆石包体，表明现代岩浆系统中存在同化始新世地壳岩石的遗迹。安山岩Santiaguito tephra中的锆石晶体与1902年浮岩中的锆石晶体在年龄和微量元素特征上相同。这是残余演化岩浆持续存在的直接证据，其结晶可追溯到约100年至25年KYR之间的圣地亚吉托锥体形成阶段和1902年之前的喷发平静阶段，持续约25KYR。这也表明残留英安岩仍对桑提亚吉托安山期岩浆有贡献。在圣地亚吉托安山岩中锆石的生存需要玄武岩安山岩和常驻英安岩岩浆之间相对较短的岩浆混合时间，否则锆石将被重新吸收。
The Santa María-Santiaguito volcanic complex collectively is one of the most active and dangerous volcanoes in the entire Central American volcanic arc. Within 20 years of the destructive Plinian eruption of the Santa María stratocone (Guatemala) in 1902, the Santiaguito volcanic dome complex started to form by parasitic vent eruptions which have lasted over nearly a century. Because of the frequent eruptions of Santiaguito, it offers unique opportunities to study secular changes in its subvolcanic magma reservoir at high temporal resolution. Ash collected days and hours after eruptions of Santiaguito during an unusually explosive interval in August 2016 represents some of the least evolved compositions (60–62% SiO2) with the lowest87Sr/86Sr isotope ratios ever reported for the system. This extends the multi-decadal trend of Santiaguito to progressively less evolved magma compositions with time, relative to the 1902 event which erupted overwhelmingly dacitic pumice. Santiaguito's geochemical changes are indicative of increasingly larger contributions of fresh basaltic andesite magma recharge mixing with dacitic magma that remained after the 1902 eruption. High-resolution secondary ion mass spectrometry (SIMS)238U-230Th disequilibrium dating and geochemistry of zircon from Santiaguito ash and Santa María 1902 pumice reveal the presence of evolved and zircon-saturated melts over the entire ca. 100 kyr interval of basaltic andesite eruptions that constructed the Santa María central cone. Quartz diorite basement xenoliths (~55% SiO2) with Eocene zircons are common in the Santa María 1902 deposits, and a few equally old zircon xenocrysts within Santiaguito ash suggest that vestiges of assimilated Eocene crustal rocks are present in the modern magma system. Zircon crystals in andesitic Santiaguito tephra are identical in age and trace element signature to those in the 1902 pumice. This is direct evidence for the persistence of residual evolved magma with crystals dating back to the Santiaguito cone-forming stage between ca. 100 and 25 ka and the pre-1902 eruptive quiescence which lasted for ca. 25 kyr. It also indicates that residual dacite still contributes to Santiaguito andesitic magmas. Zircon survival in Santiaguito andesite requires comparatively brief timescales of magma mixing between basaltic andesite and resident dacite magmas because otherwise zircon would become resorbed.
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