What are the magma fluxes required to build up magma chambers large enough to feed major ignimbrite eruptions?

To feed major ignimbrite eruptions, hundreds to thousands cubic kilometers of silicic eruptible magmas must be able to accumulate in the upper crust. A series of observations indicates that many igneous bodies grow by addition of discrete small pulses that commonly take the form of sheet intrusions. The ability of eruptible magma to accumulate within an igneous body depends on the sheets emplacement rate but the volumes of any magma chamber depend on both the emplacement rate and the extension of the intrusive sheets, i.e. on the volumetric magma flux. Short sheets that are emplaced rapidly can accumulate eruptible magma, but the cumulated magma volumes are too small to feed major ignimbrite eruptions. Long sheets emplaced slowly solidify between two intrusions, so that the size of any magma chamber does not exceed the size of one sheet intrusion. Numerical simulations of the growth of an igneous body by addition of sills show that to form magma chambers that are large enough to feed major ignimbrite eruptions, sills that are more than 10 km in diameter must be emplaced at rates exceeding several centimeters per years, which corresponds to magma fluxes of more than 0.01 cubic kilometers per year. These computed magma fluxes are one to two orders of magnitude higher than the long-term average magma fluxes inferred from geochronological studies on plutons and batholiths. This suggests that magma fluxes in the upper crust vary over several orders of magnitude and that large eruptible magma chambers are transient and form during periods of exceptionally high fluxes.