Shock-related mineralogical features and P-T history of the Suizhou L6 chondrite

The Suizhou meteorite, classified as an L6 chondrite, contains weakly shocked olivine and pyroxene, but almost all the plagioclase in the meteorite was melted and transformed into maskelynite during shock metamorphism. Chromite was heavily fragmented and granulated, and many tiny chromite fragments were incorporated into the molten plagioclase as inclusions. Metal and troilite show no obvious intragranular textures, but many tiny rounded FeNi metal grains were deposited in the intersecting joints of planar fractures in olivine and pyroxene. A few very thin shock melt veins occur in the Suizhou meteorite, which contain abundant high-pressure phases, including coarse-grained ringwoodite, majorite, (Na,Ca)AlSi3O8-hollanditc and fine-grained liquidus majorite-pyrope garnet. The shock features of this meteorite match shock stages 3 to 5, while the presence of ringwoodite in Suizhou veins is considered to appear at stage 6. It is estimated that the Suizhou meteorite experienced a shock pressure and shock temperature of up to 22 GPa and 1000 degreesC, respectively. The shearing friction along veins raised the temperature within the veins. Shock-induced pressure and temperature in the shock veins attained 22 GPa and 1900 degreesC. Therefore, the actual shock level of the Suizhou meteorite could correspond to stage 3-4. A longer duration of the shock pressure and temperature regime in the Suizhou meteorite plays an important role in the pervasive melting of plagioclase in the unmelted part of the meteorite, as well as in the formation of abundant high-pressure phases in the very thin shock-melt veins. It appears that maskelynite cannot be used as the sole criteria for evaluating the shock stage of shock-metamorphosed chondrites.