RESUMEN
Generation of silicic magmas leads to emplacement of granite plutons, huge explosive volcanic eruptions and physical and chemical zoning of continental and arc crust1-7. 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 rapid9-12. 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.
RESUMEN
In this paper we report some experimental results of a direct algorithm for the solution of digital image restoration problems. The solution is obtained directly from the system of linear equations that result from the discretization of the Fredholm integral equation of the first kind. This algorithm uses a simple regularized least-squares technique. Also, the regularization parameter for the optimum solution is calculated by a direct (noniterative) method. A computer simulated example using both space invariant and space variant spatially separable point spread functions is presented. We show that this method compares favorably with other known direct methods.