| 西藏罗布莎地幔橄榄岩变形显微构造特征及其地质意义 |
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| 引用本文： | 徐梦婧,金振民.西藏罗布莎地幔橄榄岩变形显微构造特征及其地质意义[J].地质通报,2010,29(12):1795-1803. |
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| 作者姓名： | 徐梦婧 金振民 |
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| 作者单位： | 中国地质大学(武汉)地球科学学院,湖北,武汉,430074 |
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| 摘 要： | 地幔橄榄岩是罗布莎蛇绿岩的主要组成成分之一,通过显微构造特征可对其变形特征进行分析,确定流变学参数,探讨地幔橄榄岩的变形历史。以蛇纹石化程度较低的二辉橄榄岩和方辉橄榄岩为研究对象,橄榄石位错特征研究显示,本区橄榄石主要发育了低温常见的直线型自由位错,局部可见位错弓弯、位错环、位错壁等高温位错,反映罗布莎地幔橄榄岩变形以低温塑性流变为主,局部经历了高温塑性流变,主导变形机制为位错蠕变。橄榄石自由位错统计结果表明,二辉橄榄岩中的橄榄石自由位错密度为4.422×107/cm2,方辉橄榄岩中的橄榄石为9.137×107/cm2,变形过程中所受差异应力分别为65MPa和93MPa。橄榄石和斜方辉石显微组构测量采用了电子背散射衍射技术(EBSD),分析结果表明,橄榄石均发育A型组构,为浅部地幔常见的组构类型,该结果与金刚石、柯石英等超高压矿物所指示的形成深度不一致。
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| 关 键 词： | 西藏罗布莎 地幔橄榄岩 橄榄石 位错 显微组构 |
Deformation microstructures of mantle peridotite from Luobusha ophiolite,Tibet , China and its geological implication |
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| XU Meng-jing,JIN Zhen-min.Deformation microstructures of mantle peridotite from Luobusha ophiolite,Tibet , China and its geological implication[J].Geologcal Bulletin OF China,2010,29(12):1795-1803. |
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| Authors: | XU Meng-jing JIN Zhen-min |
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| Institution: | College of Earth Science, China University of Geosciences , Wuhan 430074, Hubei, China |
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| Abstract: | Mantle peridotite is one of the main compositions of Luobusa ophiolite. According to its microstructures characteristics, we can analyze the characteristics of deformation, define rheological parameters, and investigate the deformation history of mantle peridotite. In this paper, we chose lherzolite and harzburgite with weak serpentinization degree as research objiects. Analysis of the dislocation configurations of olivine by oxidation decoration technique show that dislocation microstructures are dominant linear type free dislocation which usually forms at low temperature, and also include some high temperature dislocation, such as dislocation bows, dislocation loops and dislocation wall. The results propose that Luobusha mantle peridotite deformation is dominated by low temperature plastic flow, and some localized regions experience high temperature plastic flow. Based on the statistical analysis, free dislocation density of lherzolite is 4.422×107/cm2, while that of harzburgite is 9.137×107/cm2. Applying an olivine dislocation density piezometer, we determine that the stress on lherzolite and harzburgite during this deformation event were 65MPa and 93MPa. A-type lattice-preferred orientation (LPO) of olivine from all samples is observed by Electron Backscatter Diffraction (EBSD), which is conventional in shallow mantle. The depth is inconsistent with that indicated by diamond and coesite. |
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| Keywords: | Luobusha area Tibet mantle peridotite olivine dislocation fabric |
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