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

The Suizhou meteorite, classified as an L6 chondrite, contains weakly shock ed olivine and pyroxene, but almost all the plagioclase in the meteorite wa s melted and transformed into maskelynite during shock metamorphism. Chromi te was heavily fragmented and granulated, and many tiny chromite fragments were incorporated into the molten plagioclase as inclusions. Metal and troi lite show no obvious intragranular textures, but many tiny rounded FeNi met al 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-g rained ringwoodite, majorite, (Na,Ca)AlSi3O8-hollanditc and fine-grained li quidus majorite-pyrope garnet. The shock features of this meteorite match s hock stages 3 to 5, while the presence of ringwoodite in Suizhou veins is c onsidered 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 tempe rature within the veins. Shock-induced pressure and temperature in the shoc k veins attained 22 GPa and 1900 degreesC. Therefore, the actual shock leve l of the Suizhou meteorite could correspond to stage 3-4. A longer duration of the shock pressure and temperature regime in the Suizhou meteorite play s 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-pressu re phases in the very thin shock-melt veins. It appears that maskelynite ca nnot be used as the sole criteria for evaluating the shock stage of shock-m etamorphosed chondrites.