Wadsleyite and ringwoodite formation from melt induced by a shock event in Peace River L6 chondrite

The assemblages of wadsleyite and ringwoodite transformed from individual olivine contained in a deformed chondrule were identified in the shock melt veins of Peace River L6 chondrite. The assemblages of wadsleyite and ringwoodite were extracted by using a FIB system, and analyzed by TEM/STEM-EDS. There was obvious enrichment or depletion in Mg and Fe ratios between ringwoodite (Fo = 66) and wadsleyite (Fo = 89). Using the interdiffusion coefficients in order to check if the contrasting compositions of ringwoodite and wadsleyite, respectively could have resulted from solid-state interdiffusion alone leads to unrealistically long duration of the shock event. Few stacking faults were observed both in ringwoodite and wadsleyite thus suggesting that both minerals didn't form by a shear mechanism. The deformed chondrules are squeezed and flattened implying strong plastic deformation and partial melting. There is no evidence of mixing of melts of olivine and clinopyroxene, the latter not melted. It is considered that wadsleyite and ringwoodite successively crystallized from individual melts of the former olivine crystals alone. Wadsleyite, low in Fe, crystallized first from melt in the interior of the former olivine crystals followed by Fe-rich ringwoodite nucleating on wadsleyite thus separating it from the residual melt enriched in Fe.