| 碧溪岭石榴异剥橄榄岩的显微构造及成因机制 |
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| 引用本文： | 韦博,金振民,章军锋.碧溪岭石榴异剥橄榄岩的显微构造及成因机制[J].地球科学,2013,38(5):983-994. |
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| 作者姓名： | 韦博 金振民 章军锋 |
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| 作者单位： | 1.中国地质大学地球科学学院, 湖北武汉 430074 |
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| 基金项目： | 国家自然科学基金项目(Nos.41174076,41002068) |
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| 摘 要： | 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230~600 MPa, 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.
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| 关 键 词： | 石榴异剥橄榄岩 晶格优选方位 位错 结构水 差异应力 显微构造 |
| 收稿时间： | 2012-07-28 |
Deformation Microstructures and Mechanism of Ultrahigh-Pressure Garnet Wehrlite from Bixiling,Dabie Mountains |
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| WEI Bo;JIN Zhen-min;ZHANG Jun-feng.Deformation Microstructures and Mechanism of Ultrahigh-Pressure Garnet Wehrlite from Bixiling,Dabie Mountains[J].Earth Science-Journal of China University of Geosciences,2013,38(5):983-994. |
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| Authors: | WEI Bo;JIN Zhen-min;ZHANG Jun-feng |
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| Institution: | WEI Bo;JIN Zhen-min;ZHANG Jun-feng;Faculty of Earth Sciences,China University of Geosciences;State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences; |
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| Abstract: | Studies of deformed microstructures of peridotite in ultrahigh-pressure metamorphic belt are conductive to understand rheological property and deformation mechanism of mantle materials derived from plate boundary, then further to explore the effect of microstructures during geodynamic process of the deep subduction and exhumation. Deformed microstructures of garnet wehrlite from Bixiling, Dabie Mountains are systematically studied through optical microscope, electron probe, infrared spectroscopy, electron back scattered diffraction (EBSD) technique and the method of oxidation decoration. Results show that: (1) garnet wehrlite from Bixiling with strong shape preferred orientation (SPO), but only clinopyroxene with strong lattice preferred orientation (LPO) and olivine with weak lattice preferred orientation, which is obviously different from the common characteristics of mantle peridotite which exhibits the stronger fabric in olivine than in clinopyroxene and in addition, reflects that clinopyroxene deforms through dislocation creep but olivine through grain boundary sliding with the adjustment of dislocation; (2) certain content of structural water are contained in clinopyroxene and olivine of garnet wehrlite from Bixiling, clinopyroxene with 124×10-6-247×10-6 and olivine with 38×10-6-80×10-6, which are higher than that in minerals of general peridotite in orogenic belt and may reflect the environment with high water content caused by the contamination of crust material; (3) significant dislocation microstructures developed in olivine and 230-600 MPa of differential stress calculated by the dislocation microstructures which is higher than the steady flow stress of normal upper mantle and indicates that our samples once have experienced the relative low-temperature deforming environment in subduction zone. Comprehensive study shows that the relatively special deforming microstructures in olivine and clinopyroxene from Bixiling attribute to the high pressure, low temperature, high differential stress and structural water content in ultrahigh-pressure metamorphic belt. |
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