The Impact of Matrix Rheology on Stress Concentration in Embedded Brittle Clasts

Abstract Frictional failure is the dominant deformation mechanism for rocks in upper crust while middle begin to deform viscously. Within this transition, brittle and viscous phases coexist, forming semi‐frictional materials. While on large scales might play an important role understanding transition between earthquakes slow slip/creep, it can also be observed at smaller scales. Here, we use field observations of Papoose Flat pluton eastern California study heterogeneous materials during shearing. Clast concentration varies 2% 12% by area. Field microscopic show that matrix deforms viscously, clasts fail a manner. We systematically document clast spacing with respect fracturing observe increasing frictional concentration. To test which viscosities impose enough stresses lead deformation, complement 2D numerical models. Maps 7% area randomly placed circular are created deformed under simple shear kinematic conditions. different viscosities, from constant low high viscosity (10 17 10 19 Pa.s, respectively), dislocation creep granite. Clasts vicinity other affected around their neighbors. This effect decreases distance. Our results suggest phase significant onto phase, causing even very concentrations absence clast‐clast interactions.