• Redistribution of elements in the heavily shocked Yanzhuang chondrite

      Kong, P.; Xie, X. (The Meteoritical Society, 2003-01-01)
      Compositions of metal, sulfide, olivine, pyroxene, and plagioclase/plagioclase glass were studied for the melted and unmelted parts of the heavily shocked H6(S6) chondrite-Yanzhuang. We found that the partitioning of some trace elements significantly changed between the 2 parts; compared with the corresponding minerals in the unmelted part, Ga is enriched in the metal, Co, Cr, and Zn are enriched in the sulfide, Cr is enriched in olivine and pyroxene, and Ti is enriched in the plagioclase glass of the melt pocket. These detailed studies of the mineral phases put constraints on 3 important parameters (temperature, pressure, and duration) associated with the post-shock melting process. The coexistence of melted and unmelted olivine in the melt pocket of Yanzhuang implies a peak temperature after shock that approaches the melting point of olivine. The lack of Ni in the olivine crystallized from a melt suggests crystallization of olivine at pressures below 10 kbar. The resetting of Ga partitioning between metal and silicate in the melt pocket indicates that the interval from the peak temperature after shock to the crystallization of metal-sulfide and plagioclase glass in the melted part of Yanzhuang is longer than 500 sec.
    • Two distinct assemblages of high-pressure liquidus phases in shock veins of the Sixiangkou meteorite

      Chen, M.; Xie, X. (The Meteoritical Society, 2008-01-01)
      Shock-produced complex veins, including earlier and later veins, are identified in the Sixiangkou L6 chondrite. The early vein is intersected by the late vein and consists of coarse-grained aggregates of ringwoodite, majorite, and lingunite, and fragments of olivine, pyroxene, plagioclase, metal, and troilite, as well as a fine-grained matrix of garnet, ringwoodite, metal, and troilite. The late vein mainly consists of a fine-grained matrix of garnet, magnesiowstite, metal, and troilite, as well as a small amount of coarse-grained aggregates. The amount of fine-grained matrix suggests that the late vein was nearly completely melted, whereas the early vein underwent partial melting. Both fine-grainedassemblages of garnet plus ringwoodite in the early vein and garnet plus magnesiowstite in the late veinare liquidus phases crystallized from shock-induced melt. Based on our understanding of the liquidus assemblages, the late vein experienced a higher pressure and temperature than the early vein.