School of Earth Sciences, University of Bristol, Bristol, UK.
Scottish Universities Environmental Research Centre, East Kilbride, UK.
Nature. 2022 Aug;608(7921):87-92. doi: 10.1038/s41586-022-04921-9. Epub 2022 Aug 3.
Generation of silicic magmas leads to emplacement of granite plutons, huge explosive volcanic eruptions and physical and chemical zoning of continental and arc crust. Whereas timescales for silicic magma generation in the deep and middle crust are prolonged, magma transfer into the upper crust followed by eruption is episodic and can be rapid. Ages of inherited zircons and sanidines from four Miocene ignimbrites in the Central Andes indicate a gap of 4.6 Myr between initiation of pluton emplacement and onset of super-eruptions, with a 1-Myr cyclicity. We show that inherited zircons and sanidine crystals were stored at temperatures <470 °C in these plutons before incorporation in ignimbrite magmas. Our observations can be explained by silicic melt segregation in a middle-crustal hot zone with episodic melt ascent from an unstable layer at the top of the zone with a timescale governed by the rheology of the upper crust. After thermal incubation of growing plutons, large upper-crustal magma chambers can form in a few thousand years or less by dike transport from the hot-zone melt layer. Instability and disruption of earlier plutonic rock occurred in a few decades or less just before or during super-eruptions.
硅质岩浆的产生导致了花岗岩岩体的就位、巨大的爆发性火山喷发以及大陆和弧地壳的物理和化学分带。虽然深中和地壳中硅质岩浆的产生时间尺度较长，但岩浆向地壳上部的迁移和随后的喷发是间歇性的，可能很快。安第斯山脉中部四个中新世火山灰流中的四个继承锆石和钠闪石的年龄表明，岩体就位和超级喷发开始之间存在 460 万年的间隔，具有 100 万年的周期性。我们表明，在被火山灰熔体包裹之前，这些岩体中的继承锆石和钠闪石晶体以 <470°C 的温度储存在这些岩体中。我们的观察结果可以用中地壳热区中的硅质熔体分离来解释，熔体在不稳定层的顶部从热区周期性上升，时间尺度由上地壳的流变学决定。在生长中的岩体热孵化之后，通过来自热区熔体层的岩脉输送，在几千年或更短的时间内可以形成大的上地壳岩浆房。超级喷发之前或期间，早期的侵入岩岩石在几十年或更短的时间内发生不稳定性和破坏。
