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对超高压变质带中橄榄岩变形显微构造的研究,有助于了解板块边界构造环境中地幔物质的流变性质和变形机制,进而探讨其在深俯冲/折返过程中的地球动力学过程的作用.采用光学显微镜、电子探针、红外光谱、电子背散射衍射(EBSD)、位错氧化缀饰等多种方法系统研究了来自中国大别碧溪岭的石榴异剥橄榄岩中的变形显微构造.研究结果表明:(1)碧溪岭石榴异剥橄榄岩发育较好的形状优选方位,但只有单斜辉石显示了强晶格优选方位,而橄榄石晶格优选方位很弱,与常见上地幔橄榄岩中单斜辉石组构弱而橄榄石组构强的特点差异显著,反映了单斜辉石经历位错蠕变而橄榄石经历位错调节的颗粒边界滑移变形;(2)碧溪岭异剥橄榄岩中单斜辉石和橄榄石均含有一定量的结构水,其中单斜辉石含水量124×10-6~274×10-6,橄榄石含水量38×10-6~80×10-6,高于常见造山带橄榄岩中各矿物的含水量,可能反映了壳源物质混染引起的高含水量变形环境;(3)橄榄石中发育显著位错显微构造,根据位错显微构造计算的变形差异应力为230~600MPa,高于正常上地幔稳态流变应力,反映了俯冲带中的相对低温变形环境.综合分析研究表明,超高压变质带中的高压、低温、高差异应力和高结构水含量是形成碧溪岭相对独特的橄榄石、单斜辉石变形显微构造的原因.
The study of the deformation microstructure of peridotites in the UHPM metamorphic belt can help to understand the rheological properties and deformation mechanisms of mantle materials in the tectonic setting of the plate boundary so as to explore the geodynamic processes in the deep subduction / The morphologies of pomegranate deparaxized peridotites from Bixi Ridge, Dabie, China, were studied systematically by means of optical microscope, electron probe, infrared spectroscopy, electron backscatter diffraction (EBSD) The results show that: (1) The birch dementional peridotites have better shape orientation, but only the clinopyroxene shows strong lattice preferred orientation, while the olivine lattice preferred orientation is very weak, Compared with the weak peridotite structure and the strong olivine structure in the common upper mantle peridotite, the grain boundary slip deformation of the clinopyroxene undergoes dislocation creep and the olivine undergoes dislocation regulation. (2) Both clinopyroxene and olivine in the Bixi dedesperoxenite contain a certain amount of structural water, of which the clinopyroxene water content is 124 × 10-6 ~ 274 × 10-6, the olivine water content is 38 × 10-6 ~ 80 × 10-6, higher than the common orogenic peridotite The water content of the mineral may reflect the high water content deformation environment caused by the contamination of the shell material. (3) The significant dislocation microstructure develops in the olivine. The differential stress calculated according to the dislocation microstructure is 230-600 MPa , Which is higher than the steady flow stress of normal upper mantle and reflects the relative low temperature deformation environment in the subduction zone.The comprehensive analysis shows that the high pressure, low temperature, high differential stress and high structure water content in the ultrahigh pressure metamorphic belt are formed by Bixi Ridge is relatively unique olivine, clinopyroxene deformation microscopic reasons.