Spherulitic omphacite in pseudotachylytes: Microstructures related to fast crystal growth from seismic melt at eclogite-facies conditions

摘要: Abstract The microstructures and microtexture of omphacite spherulites from an eclogite-facies pseudotachylyte central Zambia was studied by electron backscattered diffraction transmission microscopy. spherulitic growth is characteristic for fast rates at high undercoolings resulting quenching a melt seismic origin to the conditions. Its preservation constrains that no significant deformation present after event during uplift. analysis grain misorientations in indicates – addition overall radial alignment grains crystallization took place highly viscous medium, which does not allow reorientation growth. microstructure diverse ambiguous: Grain contacts appear both curved with 120° triple junctions few recrystallized grains. Dislocations are frequent, but heterogeneously distributed occur dislocations networks, subgrain boundaries as free locally densities. Planar defects (chain multiplicity faults parallel (0 1 0) ending partial dislocations) abundant, while twinning (1 0 0) rare. Anti-phase domains variable domain sizes within single disappearance walls around planar constrain most must be formed or shortly crystallization. Omphacite commonly discussed result deformational stresses due tectonic forcing. Here, we hypothesize thermal stress also can provide feasible explanation this melt-grown followed recovery under static observation exclude repeated loading shear veins general, suggest only latest preserved samples fine-grained texture spherulites. Moreover, anti-phase rock uplifted rather event.