Repacking Accelerates High‐Silica Melts Extraction: Insights From Microstructural Record and Numerical Modeling

Abstract

Abstract Repacking enhances crystal mush permeability, accelerating melt extraction. However, identifying microstructural records of repacking is challenging, creating a gap in quantifying its effect on magmatic reservoirs. We identified extracted melt (rhyolite) and silicic residue (quartz monzonite) through textures and geochemical characteristics in the Pangduo Basin (Southern Tibet; ∼50 Ma old). By calculating interstitial mineral proportions and modeling incompatible element concentrations in quartz monzonite, we estimate a moderate trapped melt fraction (∼50 vol. %), providing microtextural evidence of repacking at intermediate crystallinities. We interpret that the horizontal preferred orientation of frame‐forming feldspars produces micro‐scale melt channels that accelerate melt extraction. Modeling the intensity of this orientation, we estimated compressive strain to be 20%–30%, likely accelerating melt extraction by at least 15 times. This millennium timescale allows for the growth of a large magma chamber, preventing the melt from freezing or causing multiple small eruptions due to excessive flow‐induced stress.

Keywords

• repacking
• high‐silica rhyolite
• melt extraction
• crystal mush