Shear-induced dilation, dike formation and melt segregation during mush deformation [DATA]

Description

Data accompanying manuscript of the same name. "Here we present results of high-temperature, high-pressure experiments that test the conditions leading to melt migration in mushes. Our samples were made up of juxtaposed pierces of soda-lime glass and a densified mixture of borosilicate glass and quartz sand (X = 0.65 to 0.83). When these materials are subjected to high temperatures and confining pressures (900°C, 200 MPa) they are proxies natural silicate melts and mushes, respectively (Ryan et al., 2022). We deformed these samples in torsion and observed migration of melt into the mush as a result of shear. In samples with intermediate (X = 0.75) and high (X = 0.83) mush crystal fractions melt-filled dikes formed and propagated within the mush. To our knowledge these are the first instances of dike formation and propagation in high-temperature, high-pressure deformation experiments. The dikes formed as a result of shear-induced dilation, a process that was recognized in other granular media ∼150 years ago (Reynolds, 1885) but is rarely invoked as a potential deformation behavior for mushes (Petford et al., 2020). We use our experimental results to identify the conditions for shear-induced dilation and diking in mushes, apply this analysis to an active volcanic system (Soufrière Hills Volcano, Montserrat, W.I.) and, finally, consider the role of dike formation and propagation in mushes in the rapid generation and transport of crystal-poor magmas." Imaging: "BSE mosaics of transverse sections of each experimental product were captured using a JEOL JXA-8530FPlus Electron Probe Microanalyzer (15 kV, 10 nA). Compositional differences between quartz, olivine, soda lime and borosilicate mean each phase is distinguishable based on its greyscale. Each sample was ground, polished and imaged four to ten times to produce serial sections. The area fraction of soda-lime glass that migrated into the mush (A) was quantified by thresholding and filtering BSE mosaics using ImageJ (Abramoff et al., 2004). Euclidean distance maps were thresholded to identify regions of soda-lime glass that have dimensions less than and greater than the estimated interparticle distance (40 μm; Supplement 2). Aintru is the area fraction of soda-lime glass in the mush with dimensions greater than the interparticle distance. The spatial distribution of soda-lime glass in the mush was quantified by overlaying rectangular grids on the BSE mosaics and measuring the area fractions greater and less than the interparticle distance (Supplement 2)."

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