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Melt Loss by Repacking in Magma Mushes: Analogue Phase Separation Experiments and Natural Systems

Darien Florez1 , Matej Pec1, Christian Huber2, Olivier Bachmann3, Edgar Marc Parmentier2, Hoagy Ghaffari1

  • Affiliations: 1Department of the Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA 2Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, USA 3Department of Earth Sciences, ETH Zurich, 8092 Zürich, Switzerland

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 278

  • Programme No: 1.3.21

  • Theme 1 > Session 3

Abstract

The mechanism by which crystal-melt mixtures separate is melt fraction sensitive and controls the physical and chemical evolution of magma mushes. Here, we present analogue phase separation experiments and samples from the Spirit Mountain Batholith (SMB) which show that in crustal magma reservoirs, separation by repacking (crystal rotation and translation) plays a major role. The experiments were conducted on mixtures of analog rigid particles and viscous liquid in a French press-like apparatus. During the experiments we monitor the samples with a video camera and an ultrasonic probe array and retrieve stress, strain rate, and bulk melt fraction. In SMB samples, fabric strength and estimates of trapped melt fraction using trace element modeling were obtained. Strains of ca. 10% were recorded between the start and end of experiments in the mush analogs. Particle-tracking analysis reveals that repacking is ubiquitous throughout the analog mush and that occasional jamming events must be overcome to resume repacking. Ultrasonic sensors were used to record acoustic emissions that accompany repacking. Similarly, repacking seems to play an important role in natural systems, as revealed by the correlation between trapped melt fraction and foliation development in SMB samples. Finally, the minimum trapped melt fraction calculated in the SMB is consistent with the that measured in the experiments (ca. 0.3). This value is consistent with the maximum packing fraction, which demarcates a transition from melt extraction by repacking (efficient melt extraction) to extraction by viscous creep (inefficient melt extraction).