Linking rapid magma reservoir assembly and eruption trigger mechanisms at evolved Yellowstone-type supervolcanoes
Linking rapid magma reservoir assembly and eruption trigger mechanisms at evolved Yellowstone-type supervolcanoes
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DOI：
10.1130/g35979.1
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发表时间：
2014-09
期刊：
影响因子：
5.8
通讯作者：
J. Wotzlaw;I. Bindeman;K. Watts;A. Schmitt;L. Caricchi;U. Schaltegger
中科院分区：
文献类型：
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作者：
J. Wotzlaw;I. Bindeman;K. Watts;A. Schmitt;L. Caricchi;U. Schaltegger
地质记录包含火山爆发的证据，这些火山爆发比现代文明经历的最大规模的爆发，即公元1815年的坦博拉（印度尼西亚）爆发大两个数量级。也许地球上没有任何地方比蛇河平原-黄石高原（SRP-YP）火山区（美国西北部）更突出的这种超级爆发的沉积物。虽然黄石公园的岩浆活动仍在进行中，但爱达荷州东部的海瑟火山区代表了SRP-YP中最年轻的完整破火山口周期，因此对黄石公园当前和未来的火山活动特别有指导意义。海瑟火山口周期在4.5 Ma前的1800 km 3基尔戈尔凝灰岩喷发中达到顶峰。副锆石在基尔戈尔凝灰岩显示显着的晶间和晶内氧同位素的不均匀性，绝大多数是18 O亏损。这表明，锆石结晶从同位素不同的岩浆批次，产生的再熔融subcaldera火山口岩石以前改变了低δ 18 O的大气热液流体。在喷发之前，这些岩浆批次被聚集并均匀化成一个单一的巨大水库。采用化学磨蚀-同位素稀释-热电离质谱法对同位素组成不同的锆石进行U-Pb年代学研究，获得了不可分辨的结晶年龄，其加权平均206 Pb/238 U年龄为4.4876 ± 0.0023Ma（MSWD = 1.5; n = 24）。这些锆石结晶年龄也无法区分透长石40 Ar/39 Ar年龄，因此锆石结晶接近喷发。这就要求在我们的地质年代学的分辨率（103-104年）内，浅地壳熔融、孤立批次组装成超级火山岩浆库、均质化和喷发发生得非常迅速。储层配置的晶体尺度图像，与几个孤立的岩浆批次，是非常相似的储层配置推断地震数据在活跃的超级火山。垂直分布在上地壳数公里的岩浆批次的连接将导致浮力超压的大幅增加，提供了一个喷发触发机制，这是储层组装过程的直接结果。
The geological record contains evidence of volcanic eruptions that were as much as two orders of magnitude larger than the most voluminous eruption experienced by modern civilizations, the A.D. 1815 Tambora (Indonesia) eruption. Perhaps nowhere on Earth are deposits of such supereruptions more prominent than in the Snake River Plain–Yellowstone Plateau (SRP-YP) volcanic province (northwest United States). While magmatic activity at Yellowstone is still ongoing, the Heise volcanic field in eastern Idaho represents the youngest complete caldera cycle in the SRP-YP, and thus is particularly instructive for current and future volcanic activity at Yellowstone. The Heise caldera cycle culminated 4.5 Ma ago in the eruption of the ∼1800 km3 Kilgore Tuff. Accessory zircons in the Kilgore Tuff display significant intercrystalline and intracrystalline oxygen isotopic heterogeneity, and the vast majority are 18O depleted. This suggests that zircons crystallized from isotopically distinct magma batches that were generated by remelting of subcaldera silicic rocks previously altered by low-δ18O meteoric-hydrothermal fluids. Prior to eruption these magma batches were assembled and homogenized into a single voluminous reservoir. U-Pb geochronology of isotopically diverse zircons using chemical abrasion–isotope dilution–thermal ionization mass spectrometry yielded indistinguishable crystallization ages with a weighted mean 206Pb/238U date of 4.4876 ± 0.0023 Ma (MSWD = 1.5; n = 24). These zircon crystallization ages are also indistinguishable from the sanidine 40Ar/39Ar dates, and thus zircons crystallized close to eruption. This requires that shallow crustal melting, assembly of isolated batches into a supervolcanic magma reservoir, homogenization, and eruption occurred extremely rapidly, within the resolution of our geochronology (103–104 yr). The crystal-scale image of the reservoir configuration, with several isolated magma batches, is very similar to the reservoir configurations inferred from seismic data at active supervolcanoes. The connection of magma batches vertically distributed over several kilometers in the upper crust would cause a substantial increase of buoyancy overpressure, providing an eruption trigger mechanism that is the direct consequence of the reservoir assembly process.