碧溪岭超高压石榴橄榄岩的流变学研究

RHEOLOGICAL RESEARCH INTO BIXILING ULTRA_HIGH_PRESSURE PERIDOTITE IN DABIE MOUNTAINS

从组构、位错、滑移系及古应力计算等方面综合研究了大别山超高压石榴橄榄岩的流变学特征 .(1 )对橄榄岩中单斜辉石和斜方辉石的组构分析表明 ,碧溪岭地区超基性岩经历了塑性变形 ,形成了LPO组构 ;碧溪岭超基性岩的变形特征既不类似于蛇绿岩 ,也不完全等同于幔源包体 ,它有十分独特的变形图象 .(2 )利用费氏台可观测到的滑移系有如下两种 :[0 0 1 ](1 0 0 )为中高温滑移系 ,[0 1 0 ](1 0 0 )为低温滑移系 .低温滑移系和高温滑移系的共存 ,说明该岩块至少经历过两期塑性变形 .(3)用位错密度法计算的古应力为 :Δσ =7.2 7MPa .(4)氧化缀饰法薄片所揭示的橄榄石位错组态主要有自由位错、位错壁、亚颗粒构造、位错网构造、位错环构造 。

The rheological features of Bixiling ultra_high_pressure garnet peridotite in Dabie mountains are studied in terms of fabric, dislocation, glide system and paleo_stress computation. (1) The fabric analysis of Cpx and Opx in peridotite indicates that the Bixiling ultra_basic rocks has experienced the ductile deformation, resulting in the LPO fabric. The very unique deformed image of the Bixiling ultra_high_pressure garnet peridotite is different not only from that of the ophiolite but also from that of the mantle xenlolith. (2) The glide system measured with universal stage is classified as the following two categories: [001](100) as a medium_high_temperature deformation and [010](100) as a low_temperature deformation. The coexistence of the low_temperature deformation and the high_temperature deformation indicates that this rock has experienced at least two phases of plastic deformation. (3) The paleo_stress obtained with the dislocation density is Δ σ =7.27?MPa. (4) The dislocation fabric forms revealed through the thin sheets tested with the oxidization ornamentation method are categorized as the free dislocation, dislocation wall, sub_grain structure, dislocation net structure and dislocation ring structure, indicating that the olivine in this region has experienced a strong ductile deformation.