Abstract
Here we report for the first-time shock-induced incongruent melting of
olivine in an ordinary chondrite. Several olivine grains (Fo74),
entrained in the shock-melt vein of the Kamargaon L6 chondrite were
dissociated into magnesiowüstite (XFe = 0.71) and orthoenstatite (XFe =
0.22). We propose that the breakdown of olivine took place as a result
of incongruent melting to produce magnesiowüstite and Mg-rich liquid. We
suggest that bridgmanite may have crystallized as the second phase from
the olivine melt which back-transformed to a low-pressure phase of
orthoenstatite from subsequent high-temperature and low-pressure events.
In this case, olivine grains may have experienced pressure and
temperature of ~25 GPa and ~2500 °C,
respectively. Our results suggest that the incongruent melting of
olivine may possibly operate as one of the alternative mechanisms of
dissociation reaction driving the phase transformation of olivine in the
natural systems.