Nanoscale earthquake records preserved in plagioclase microfractures from the lower continental crust

Abstract. Seismic faulting causes wall rock damage, which is driven by both mechanical and thermal stress. In the lower crust, co-seismic damage increases permeability, permits fluid infiltration triggers metamorphic reactions that transform rheology. Wall microstructures reveal high-stress conditions near earthquake faults; however, there limited documentation on effects of a pulse coupled with infiltration. Here, we present transmission electron microscopy study microfractures in plagioclase feldspar from crustal granulites Bergen Arcs, Western Norway. Focused ion beam foils are collected 1.25 mm 1.8 cm 1.3 thick eclogite facies pseudotachylyte vein. Dislocation-free K-feldspar aggregates record history introduction recovery short-lived state caused slip along nearby fault. The retain crystallographic orientation their host elongated subparallel to pseudotachylyte. We propose partially amorphized at peak stress followed repolymerization form dislocation-free grain aggregates. Repolymerization recrystallization were enhanced fluids transported Ca K into microfractures. Subsequent cooling led exsolution intermediate compositions formation Bøggild–Huttenlocher intergrowth grains fracture closest Our findings provide unequivocal evidence occurred within timescale perturbation, prompting rapid annealing damaged soon after rupture.