GEOCHEMISRY OF THE MYLONITIZED SILICEOUS BANDED LIMESTONE IN CENTRAL LANGSHAN AREA, INNER MONGOLIA
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摘要:
狼山构造带是华北地台北缘巨型造山带的重要组成部分，韧性剪切带是狼山构造带内的主要构造形式之一，是地壳深层次构造的反映.对狼山Ⅱ号韧性剪切带西南缘糜棱岩化硅质条带状灰岩进行地球化学特征研究，以探讨不同变形强度的糜棱岩化硅质条带状灰岩与原岩的成分变异规律.常量元素、微量元素和稀土元素分析结果表明，与原岩中常量元素和微量元素含量相比较，变形强度不同的硅质条带状灰岩存在着差异变化.变形岩石中常量元素仅CaO为带出组分，其他均为带入组分；微量元素中富集Rr、Sr、Ba、Pb、Ti、Cr、Cu、Nb、Ta、Zr、Hf元素，Ni元素相对亏损.变形的硅质条带状灰岩与原岩的稀土元素配分模式图基本一致，表现为轻稀土元素富集、重稀土元素亏损的右倾斜曲线，具有明显的负Eu异常特征，表明稀土元素在韧性剪切过程中具有一定的相对稳定性和同源性.
Abstract:The Langshan tectonic belt is an important part of the giant orogenic belt in the north margin of North China Platform, with ductile shear zone as one of the major structural styles, reflecting deep structure of the crust. The geochemical characteristics of the mylonitized siliceous banded limestone in the southwest of Langshan Ⅱ ductile shear zone are discussed to study the composition changes of the mylonitized rock from protolith in different deformation strength. The analysis results show that, compared with the content of the protolith, there are differences of major and trace elements in the siliceous banded limestone by deformation strength. Among the major elements of deformed rocks, only CaO is the exported component, all the others are imported ones. The trace elements such as Rr, Sr, Ba, Pb, Ti, Cr, Cu, Nb, Ta, Zr and Hf are enriched and Ni relatively deficient. The REE distribution patterns of deformed siliceous banded limestone and protolith are basically consistent, which are characterized by right-dipping curves with enrichment of LREEs and depletion of HREEs, and obvious negative Eu anomaly, indicating the REEs have relative stability and homology during ductile shearing.
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表 1 硅质条带状灰岩样品常量元素分析结果表
Table 1. Major element contents in siliceous banded limestone samples
岩石 未变形条带状灰岩 初糜棱岩 糜棱岩 超糜棱岩 含量/% K 含量/% K 含量/% K 含量/% K SiO2 7.55 1 11.84 1.56 15.49 2.05 44.74 5.92 Al2O3 0.571 1 2.44 4.27 3.43 6 3.26 5.71 Fe2O3 0.347 1 1.49 4.29 2.82 8.12 2.92 8.41 MgO 1.07 1 3.93 3.67 1.35 1.26 2.34 2.19 CaO 51.14 1 43.68 0.85 42.66 0.83 26.02 0.51 Na2O 0.028 1 0.113 4.03 0.16 5.71 0.185 6.6 K2O 0.055 1 0.757 1.5 1.24 22.5 1.05 19.01 MnO 0.02 1 0.051 2.5 0.059 2.95 0.338 16.9 TiO2 0.051 1 0.179 3.5 0.374 7.3 0.247 4.84 P2O5 0.048 1 0.051 1.06 0.086 1.79 0.095 1.98 FeO 0.28 1 1.3 4.64 2.52 9 2.38 8.5 烧失量 38.03 1 34.14 29.07 16.4 总量 99.19 1 99.971 99.259 99.975 测试单位：北京核工业地质研究院，2015. 
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表 2 硅质条带状灰岩样品微量元素分析结果表
Table 2. Trace element contents in siliceous banded limestone samples
岩石 未变形条带状灰岩 初糜棱岩 糜棱岩 超糜棱岩 含量/10-6 K 含量/10-6 K 含量/10-6 K 含量/10-6 K Rb 0.208 1 32 153.0 34.2 164.4 37.8 181.7 Sr 0.612 1 657 1073.5 414 676.5 263 429.7 Ba 4.81 1 404 84.0 267 55.6 251 52.2 Pb 2.09 1 4.39 2.1 15.2 7.3 8.83 4.2 Ti 0.004 1 0.16 40 0.159 39.75 0.214 53.5 Cr 5.67 1 11.1 1.96 13.6 2.4 15.6 2.75 Ni 24 1 21.6 0.9 19.1 0.79 23.1 0.96 Cu 2 1 3.66 1.83 9.41 4.705 14.7 7.35 Nb 0.785 1 5.3 6.75 5.8 7.39 16.5 21.02 Ta 0.048 1 0.403 8.4 0.941 19.6 0.31 6.46 Zr 20.3 1 38.6 1.9 40 1.97 80.2 3.95 Hf 0.547 1 1.1 2.01 1.4 2.56 1.93 3.53 测试单位：北京核工业地质研究院，2015.
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表 3 硅质条带状灰岩样品稀土元素分析结果表
Table 3. REE contents in siliceous banded limestone samples
岩石 未变形条带状灰岩 初糜棱岩 糜棱岩 超糜棱岩 含量/10-6 K 含量/10-6 K 含量/10-6 K 含量/10-6 K La 5.05 1 14.2 2.81 15.6 3.08 13.5 2.67 Ce 7.4 1 24.2 3.27 32.7 4.42 26.5 3.58 Pr 1.06 1 2.96 2.79 4.13 3.89 3.42 3.20 Nd 4.26 1 11.7 2.75 17.7 4.15 14.7 3.45 Sm 0.819 1 2.19 2.67 4.29 5.24 3.34 4.07 Eu 0.125 1 0.478 3.82 1.17 9.36 0.659 5.27 Gd 0.931 1 2.22 2.38 4.2 4.51 3.55 3.81 Tb 0.13 1 0.363 2.79 0.802 6.17 0.648 4.98 Dy 0.853 1 1.73 2.03 3.77 4.42 3.49 4.09 Ho 0.158 1 0.377 2.37 0.665 4.21 0.68 4.03 Er 0.512 1 1.01 1.97 1.75 3.42 1.78 3.48 Tm 0.08 1 0.156 1.95 0.241 3.01 0.288 3.6 Yb 0.527 1 0.935 1.77 1.48 2.81 1.88 3.57 Lu 0.057 1 0.114 2.00 0.181 3.16 0.257 4.51 Y 6.15 1 11.4 1.85 19.7 3.20 19.8 3.22 ΣREE 21.962 1 62.63 2.85 88.68 4.03 74.69 3.40 LREE 18.714 1 55.73 2.98 75.59 4.04 62.12 3.32 HREE 3.248 1 6.90 2.12 13.09 4.03 12.57 3.87 LREE/HREE 5.762 1 8.07 5.78 4.94 （La/Yb）N 6.48 1 10.26 7.12 4.85 δEu 0.44 1 0.66 0.84 0.58 δCe 0.75 1 0.87 0.95 0.914 测试单位：北京核工业地质研究院，2015.
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