Raman spectroscopy of high-pressure phases in shocked L6 chondrite NWA 5011

Abstract

In the paper we present results of studies of thick shock melt veins in NWA 5011 L6 chondrite. The veins contain a wide variety of high-pressure phases that correspond to contrast values of pressure-temperature parameters on equilibrium phase diagrams. Olivine was transformed to ringwoodite and wadsleyte, orthopyroxene to majorite, akimotoite, and bridgmanite glass, maskelenite is converted to jadeite (+SiO2) and lingunite, apatite to tuite, and chromite to the phase with the calcium ferrite (mCF-FeCr2O4) structure. ) The peak PT shock parameters for NWA 5011 seem highest among the ones for other shocked chondrites according to wide occurrence of lingunite and bridgmanite glass and are considerable higher than 25 GPa and 2500 K. Akimotoite crystals in a quenched matrix of shock melt veins were found for the first time. Probably, they initially crystallized as bridgmanite, since akimotoite is not a liquidus phase in related systems. Plagioclase-chromite aggregates have been established, which characterize the late stages of the shock process and are formed during successive crystallization from isolated pockets of the impact melt.

Impact dynamics of the L chondrites' parent asteroid

“…Given the composition (especially the forsterite percentage) of olivine, we infer that the liquidus temperature is closer to the Allende meteorite, hence about 2400 K. The presence of lingunite in Sixiangkou and Tenham suggests a temperature around 2250–2450 K (Wang & Takahashi, 1999). Finally, according to Litasov and Badyukov (2019), the triple point majorite–akimoite–bridgmanite is around 2400 K as well. Therefore, we choose a temperature of 2400 K for our calculations, for all meteorites.…”