Shock effects and the classification of H-chondrites from the Grove Mountains,East Antarctica:Implications for the shock history of H-chondrite parent bodies  

作　　者：WANG BaoHua MIAO BingKui WANG Jiang ZHANG Jian 

机构地区：[1]Key Laboratory of Geological Engineering Centre of Guangxi Province, Guilin University of Technology, Guilin 541004, China [2]College of Earth Sciences, Guilin University of Technology, Guilin 541004, China

出　　处：《Advances in Polar Science》2011年第2期81-91,共11页极地科学进展（英文版）

基　　金：supported by the Pilot Project of Knowledge Innovation of Chinese Academy of Sciences (Grant no.KZCX2-YW-110);the National Natural Science Foundation of China(Grant nos. 40673055 and 40473037);the Open Foundation of Key Laboratory of Geological Engineering Centre of Guangxi Province (Grantno. Gui Ke Neng 07109011-K024)

摘　　要：The shock metamorphism of 47 H group chondrites （H-chondrites） from the Grove Mountains including undulatory extinction, planar fractures, mosaic extinction, shock veins and pockets, and dendritic eutectic metal-sulfide, is observed through optical microscope. The textures and assemblages of shock veins in these H-chondrites are examined by the scanning electron microscope. Based on observations of the above shock effects, the shock stages of the 47 H-chondrites are classified into S1（5）, S2（19）,S$3（14）, S4（8） and S5（1）. Of these H-chondrites, GRV 022469 has the highest（S5） shock stage. The comparison of shock stages in these H-chondrites with L group chondrites（L-chondrites） indicates that the shock metamorphism of H-chondrites is relatively low （except for GRV 022469, they are all lower than $5）. A scenario for the history of the H-chondrite parent body is proposed that suggests the duration of the shock events in the H-chondrite parent bodies was much shorter than those in L-chondrite parent bodies. Also, the pressure may have been released more quickly, and consequently, the high-pressure phases should be easily preserved. However, the parent bodies of the H-chondrites may have been exposed to high temperatures for a longer time after the shock event, so the high-pressure phases formed by solid transformation might have retro-metamorphosed to low-pressure ones; its peak pressure is estimated to be less than 15 GPa. Wadsleyite was found in a shock vein in GRV022469, as confirmed by the Raman spectrometer. Petrological and mineralogical characteristics support the idea that the wadsleyite was formed by solid-state transformation.The shock metamorphism of 47 H group chondrites （H-chondrites） from the Grove Mountains including undulatory extinction, planar fractures, mosaic extinction, shock veins and pockets, and dendritic eutectic metal-sulfide, is observed through optical microscope. The textures and assemblages of shock veins in these H-chondrites are examined by the scanning electron microscope. Based on observations of the above shock effects, the shock stages of the 47 H-chondrites are classified into S1（5）, S2（19）,S$3（14）, S4（8） and S5（1）. Of these H-chondrites, GRV 022469 has the highest（S5） shock stage. The comparison of shock stages in these H-chondrites with L group chondrites（L-chondrites） indicates that the shock metamorphism of H-chondrites is relatively low （except for GRV 022469, they are all lower than $5）. A scenario for the history of the H-chondrite parent body is proposed that suggests the duration of the shock events in the H-chondrite parent bodies was much shorter than those in L-chondrite parent bodies. Also, the pressure may have been released more quickly, and consequently, the high-pressure phases should be easily preserved. However, the parent bodies of the H-chondrites may have been exposed to high temperatures for a longer time after the shock event, so the high-pressure phases formed by solid transformation might have retro-metamorphosed to low-pressure ones; its peak pressure is estimated to be less than 15 GPa. Wadsleyite was found in a shock vein in GRV022469, as confirmed by the Raman spectrometer. Petrological and mineralogical characteristics support the idea that the wadsleyite was formed by solid-state transformation.

关 键 词：Ordinary chondrite Grove Mountains H-chondrite shock stage WADSLEYITE 

分 类 号：P185.83[天文地球—天文学] TK229.3[动力工程及工程热物理—动力机械及工程]