Short eruption window revealed by absolute crystal growth rates in a granitic magma
Short eruption window revealed by absolute crystal growth rates in a granitic magma
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DOI：
10.1038/ngeo2185
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发表时间：
2014-07-01
影响因子：
18.3
通讯作者：
Schoene, Blair
中科院分区：
文献类型：
--
作者：
Barboni, Melanie;Schoene, Blair
灾难性火山爆发的可能性（1）取决于储存在地壳浅层储层中的岩浆的体积以及岩浆在没有冷却和结晶的情况下积累形成固体岩石的时间。岩浆储层的体积和寿命反过来又受进入系统的新岩浆的流量和储层的晶体含量控制（2-6）。为了理解为什么有些岩浆喷发，而另一些则在地壳中凝固，晶体生长和上地壳岩浆驻留的时间尺度必须从喷发的火山岩和侵入的深成岩中确定（7）。然而，我们对这些时间尺度的理解在很大程度上仅限于火山岩（8-14），而对深成岩的测量则缺失。在这里，我们使用锆石晶体的U-Pb年代测定样品从一个七百万年前的上地壳在厄尔巴岛，意大利的岩体。锆石晶体被发现作为6-8厘米长的钾长石巨晶的核心和边缘的包裹体，并限制巨晶的生长速率为0.2-1.1 μ m/年（-1）。我们结合联合收割机测量的增长率与岩石学观察和相平衡建模表明，从喷发的岩浆到不动的花岗岩浆和深成岩形成的过渡发生在短短10-40万年。这一潜在喷发的短时间窗口意味着一些岩浆在喷发前仅在上地壳储层中停留了很短的时间。
The potential for cataclysmic volcanic eruptions(1) depends on the volume of magma stored in shallow crustal reservoirs and the amount of time over which magma can accumulate without cooling and crystallizing to form a pluton of solid rock. Magma reservoir volume and longevity are, in turn, controlled by the flux of new magma into the system and the crystal content of the reservoir(2-6). To understand why some magmas erupt, whereas others solidify in the crust, the timescales for crystal growth and upper-crust magma residence must be determined from both erupted volcanic rocks and intruded plutonic rocks(7). However, our understanding of these timescales is largely restricted to volcanic rocks only(8-14) and measurements from plutonic rocks are missing. Here we use U-Pb geochronological dating of zircon crystals sampled from a seven-million-year-old upper crustal pluton in Elba, Italy. The zircon crystals were found as inclusions within the cores and rims of 6-8-cm-long potassium-feldspar megacrysts and constrain the rate of megacryst growth to 0.2-1.1 mu m yr(-1). We combine the measured growth rates with petrological observations and phase-equilibrium modelling to show that the transition from eruptible magmas to immobile granitic mush and pluton formation occurred in just 10-40 thousand years. This short time window for a potential eruption implies that some magmas reside in upper crustal reservoirs for only a brief period before eruption.