Program > Browse abstracts by speaker > Serrano Lopez Gabriel

Recent simple shear deformation experiments in mica-bearing assemblages have shown that major weakening, down to values similar to pure mica rocks, may occur in rocks containing ~30 vol % of mica. However, the evolution of deformation mechanisms governing weakening with increasing strain is poorly constrained. To address this issue, we performed a series of simple shear deformation experiments on quartz-muscovite aggregates with 30 vol % of muscovite using a Griggs-type apparatus for different amounts of strain, from gamma 0 to 6. Experiments were conducted at 800°C, 1GPa, and ė≈1x10-5s-1. Six samples were deformed: five consisted of 0.1 g of a powder composed of 30% muscovite between 62-125 µm and 70% quartz between 10-20 µm, while the fifth one consisted of 100% quartz with greater grain size (~40 µm). Samples were analyzed post-mortem by combining microstructural observations, image analysis, electron backscatter diffraction, and hyperspectral cathodoluminescence. Muscovite-quartz aggregates appear much weaker than the pure quartz sample (reaching a peak stress of 550 MPa vs. 1075 MPa for pure quartz), and as weak as quartz-phlogopite samples described in the literature. Peak stress was followed by a pronounced weakening before a steady state. With increasing strain, mica domains disaggregate into smaller clusters oriented parallel to the shear plane. The interconnectivity of mica domains mostly depends on the amount of mica and reaches its peak before the steady state. Parent quartz grains, appearing yellow in cathodoluminescence, recrystallized into blue along grain boundaries and microcracks. The grain size of quartz is reduced during the first stages of deformation. The recrystallized grains show a weak crystallographic preferred orientation that strengthens with strain. The parental grains display internal misorientation and subgrain boundaries, indicating intracrystalline deformation. Overall, grain size reduction through PS and subgrain rotation seems to control the weakening of mica-bearing rocks at peak stress conditions.