| 滇西澜沧江构造带中-南段澜沧群变质变形期次及Ar-Ar年代学约束 |
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| 引用本文： | 毕丽莎,梁晓,王根厚,张海迪,王泉,吴春娇. 滇西澜沧江构造带中-南段澜沧群变质变形期次及Ar-Ar年代学约束[J]. 地球科学, 2018, 43(9): 3252-3266. DOI: 10.3799/dqkx.2018.999 |
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| 作者姓名： | 毕丽莎 梁晓 王根厚 张海迪 王泉 吴春娇 |
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| 作者单位： | 1.中国地质大学地球科学与资源学院, 北京 100083 |
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| 基金项目： | 中央高校基本科研业务费专项资金2652014004中国地质调查局项目12120115026901国家自然科学基金青年基金项目41402177 |
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| 摘 要： | 澜沧群变质变形过程的厘定有助于揭示澜沧江构造带的演化历史.通过对双江-惠民地区出露的中-低绿片岩相变质岩系与高压变质岩系的"构造-变质"双重解析，发现澜沧群变质岩系:（1）以挤压体制下的褶劈理S2为区域性面理，浅变质岩系中石英脉条带代表的面理S1与层理S0产状一致，并在第2期强烈压扁后与S2近平行；（2）构造样式与变质变形期次在研究区域内基本一致，表现为二叠纪-三叠纪两期次中深构造层次透入性变形为侏罗纪-新生代浅-表层次变形所叠加；（3）高压变质岩记录了两个期次的深层次构造变形，电气石与石榴石变斑晶具有明显的两阶段生长模式，核部（M1aD1a）可能代表了峰期榴辉岩相变质作用，边部代表折返过程中的蓝片岩相（M1bD1b）阶段.高压变质岩与浅变质岩第2期（M2D2）构造层次及变形样式一致，代表折返后的挤压拼贴过程，两者的剪切型褶劈理S2均指示上盘S向的剪切滑动.结合新生代三江地区发生的近90°块体旋转，恢复第2期为上盘指向E的逆冲剪切作用.通过对幸福变质石英砂岩白云母、小黑江多硅白云母和蓝闪石的40Ar-39Ar定年，以及对前人小黑江蓝闪石40Ar-39Ar年龄的重新解释，共厘定出澜沧群4个构造阶段:（1）高压变质岩第1期晚期（D1b）蓝片岩相变质作用（~250 Ma）；（2）第2期（M2D2）中层次挤压（215~214 Ma）；（3）浅变质岩系第3期早期（D3a）N-S向纵弯褶皱（111.9~103.7 Ma）与晚期（D3b）逆冲（~82.28 Ma）；（4）第4期近E-W向纵弯褶皱（新生代，很可能晚于59.18 Ma）.
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| 关 键 词： | 澜沧群 变质岩系 变质变形 面理 Ar-Ar定年 年代学 |
| 收稿时间： | 2017-12-10 |
Metamorphism-Deformation Phases and Ar-Ar Chronological Constraints of the Lancang Group in the Middle and Southern Sections of the Lancangjiang Tectonic Belt,Western Yunnan |
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| Abstract: | The determination of metamorphic deformation process in Lancang Group can reveal the evolution history of Lancangjiang tectonic belt. Based on the "tectonic-metamorphic" study of the medium-low glacial facies metamorphic rocks and the high-pressure metamorphic rocks exposed in the Shuangjiang-Huimin area, this paper presents the following findings on the metamorphic rocks in the Lancang Group:(1) the Fold cleavage S2 under the extrusion system is the regional foliation. The facies S1 represented by the quartz veins in the metamorphic rocks are consistent with the S0, and S1 is nearly parallel with S2 after the second stage. (2) The tectonic pattern and the metamorphic deformation period are basically the same in the resarch area, showing two-stage middle and deep tectonic stratigraphy in Permian-Triassic, which is shallow-surface deformation superposition of the Jurassic-Cenozoic. (3) The high-pressure metamorphic rocks record two periods of deep tectonic deformation, and the tourmaline and garnet have a distinct two-stage growth pattern. The core (M1aD1a) may represent the peak eclogite facies metamorphism, The edge represents the blue lithofacies (M1bD1b) stage during the exhumation process. The high-pressure metamorphic rocks are consistent with the tectonic level and deformation pattern of the second stage (M2D2) of the metamorphic rocks, which represents the process of the compressive stress after the exhumation process. Both shear-type cleavages S2 indicate that the upper disk shear sliding toward to cleavages. Combined with the Cenozoic Sanjiang area occurred near the 90° block rotation, the recovery of the second phase of the disk against the thrust of the role of E. By the 40Ar-39Ar dating of quartz sandstone muscovite in Xingfu area, phengite and blue amphibole in Xiaoheijiang, and reinterpreting the 40Ar-39Ar age of the blue amphibole in Xiaoheijiang, it is concluded that Lancang Group has 4 tectonic stages:(1) Metamorphism of blueschist facies in the first stage (D1b) of high-pressure metamorphic rocks, ~250 Ma. (2) The second phase (M2D2) is extrusion in the middle level, 215-214 Ma. (3) The shallow metamorphic rocks N-S to the longitudinal folds belong to the third stage (D3a):111.9-103.7 Ma with the late (D3b) thrust, ~82.28 Ma. (4) The fourth period near the E-W to the vertical fold:the new generation (probably later than 59.18 Ma). |
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