Generation of silicic magmas leads to emplacement of granite plutons, huge explosive volcanic eruptions and physical and chemical zoning of continental and arc crust^{1,2,3,4,5,6,7}. Whereas timescales for silicic magma generation in the deep and middle crust are prolonged⁸, magma transfer into the upper crust followed by eruption is episodic and can be rapid^9,10,11,12. 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花岗岩岩体就位，巨大的火山爆发和大陆和弧壳的物理和化学分带^{1,2,3,4,5,6,7}。虽然深部和中地壳硅质岩浆生成的时间尺度延长了⁸，但岩浆转移到上地壳随后喷发是偶发性的，并且可以迅速^9,10,11,12. 来自安第斯山脉中部四个中新世点火岩的继承锆石和山尼丁的年龄表明，在岩体就位开始和超级喷发开始之间存在 4.6 Myr 的差距，具有 1-Myr 的周期性。我们表明，继承的锆石和 sanidine 晶体在掺入炽热岩浆之前储存在温度 <470 °C 的这些岩体中。我们的观察可以用中地壳热区的硅熔体偏析来解释，熔体从该区顶部的不稳定层上升，时间尺度由上地壳的流变学决定。在不断生长的岩体的热孵化之后，大型上地壳岩浆房可以在几千年或更短的时间内通过来自热区熔体层的堤坝迁移形成。