Three-Dimensional Configuration Analysis and Its Geological Significance of Akebasitao Pluton in West Junggar
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摘要: 西准噶尔地区广泛发育晚石炭世-二叠纪不同规模、形态各异的花岗岩体，阿克巴斯陶岩体是其中最具代表性岩体之一，但对于该岩体三维形态和侵位过程的研究尤显薄弱.基于详细的野外路线地质调查，通过对阿克巴斯陶岩体NE、NW、SE和SW侧接触边界产状、接触热变质带宽度、岩脉方位和发育程度、顶垂体和围岩捕虏体发育特征的研究，揭示出岩体NE、SE和SW侧与围岩呈低角度外倾接触，而岩体NW侧与围岩呈高角度接触.在此基础上，结合岩体出露区音频大地电磁反演结果，揭示出阿克巴斯陶岩体三维形态总体为不对称蘑菇状，岩体侵位时岩浆主要由NW向朝SE向斜向侵位，并建立了岩体的三维形态模型.阿克巴斯陶岩体三维形态的确定，揭示了西准噶尔地区晚石炭世晚期-早二叠世为后造山伸展环境.Abstract: Late Carboniferous-Early Permian post-collision plutons are extensively distributed throughout the West Junggar, Xinjiang, China, of which the Akebasitao pluton is the most distinguished one. However, investigations on the three-dimensional configuration and emplacement mechanism of the pluton remain relatively insufficient. A multidisciplinary approach, including field structure and audio magnetotelluric sounding, has been adopted for study on the Akebasitao pluton. The geological features and the audio magnetotelluric sounding exploration suggest that the pluton, with an asymmetrical mushroom-shape and slightly oblique movement of magma from NW to SE, formed in the post-orogenic extensional environment.What is more, the three-dimensional configuartion of the pluton reveals that the West Junggar was of post-orogenic extensional environment in the Late Carboniferous to Early Permian. This study has important implication for three-dimensional shape of those post-collision plutons that are widely developped in West Junggar.
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Key words:
- akebasitao pluton /
- three-dimensional configuration /
- geochemistry /
- tectonics
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图 1 研究区地质图
a.阿克巴斯陶岩体地质简图；b.研究区地质简图；c.研究区大地构造位置简图(据Yang et al., 2012改绘).1.第四系；2.中新生界地层；3.上石炭统哈拉阿拉特山组；4.下石炭统太勒古拉组上段；5.下石炭统太勒古拉组下段；6.下石炭统包古图组；7.下石炭统希贝库拉斯组；8.中泥盆统巴尔雷克组上段；9.中泥盆统巴尔雷克组下段；10.中泥盆统库鲁木迪组下段；11.超基性岩；12.二长花岗岩；13.碱长花岗岩；14.花岗闪长岩；15.石英闪长岩；16.地质界线；17.断层；18.地层产状(°)；19.年龄样采样点；20.剖面位置
Fig. 1. Geoglogical map of study area
图 2 二长花岗岩和碱长花岗岩野外地质特征
a.碱长花岗岩与二长花岗岩宏观界线；b.后期脉动侵入的二长花岗岩切割碱长花岗岩中的早期节理
Fig. 2. Geological characteristics of alkali-feldspar granite and monzonitic granite
图 3 岩体NE侧地质特征
a, b.围岩顶垂体特征；c.围岩顶垂体中发育的高角度岩脉；d.围岩顶垂体中发育的低角度岩脉；e, f.围岩捕虏体特征；g.围岩捕虏体应力应变分析；h.三维形态剖面
Fig. 3. Geological characteristics of the NE range pluton
图 4 岩体顶垂体中岩脉与围岩接触面产状的下半球极射赤平投影
Fig. 4. Stereonets (equal area, projection on lower hemisphere) show orientation of the dykes
图 5 岩体SW侧地质特征
a.围岩产状下半球极射赤平投影；b.围岩顶垂体产状下半球极射赤平投影；c.围岩捕虏体扁平面产状下半球极射赤平投影；d.顶垂体中的高角度花岗岩岩脉；e.围岩捕虏体特征；f.岩体与围岩的接触界面；g岩体SW侧顶垂体中岩脉分布特征
Fig. 5. Geological characteristics of the SW range pluton
图 6 岩体SW侧三维形态剖面(a)和岩体SE侧三维形态剖面(b)
Fig. 6. Three-dimensional shape of SW range pluton (a) and SE range pluton (b)
图 7 岩体SE侧地质特征
a~c.围岩变质重结晶镜下特征(Bio.黑云母；And.红柱石)；d.岩体SE侧地质剖面(位置见图 1a)
Fig. 7. Geological characteristics of the SE range pluton
图 8 岩体NW侧地质特征
a.岩体与围岩的接触界线；b.岩体与围岩的接触面产状下半球极射赤平投影；c.边部顶垂体与岩体的接触边界；d.内部顶垂体与岩体的接触边界；e.内部顶垂体中发育的高角度岩脉；f.围岩捕虏体应力应变分析；g.围岩捕虏体扁平面下半球极射赤平投影；h.三维形态剖面
Fig. 8. Geological characteristics of the NW range pluton
图 9 岩体大地电磁反演结果特征
a, b, c.深度分别为0 km、4 km、7 km的切片；d.NW向切片
Fig. 9. Inversion result of electromagnetic
图 10 岩体三维形态模型及剖面
a.岩体三维形态模型；b.岩体NW-SE向三维形态剖面；c.岩体NE-SW向三维形态剖面.1.石炭系地层；2.下石炭统太勒古拉组上段；3.下石炭统太勒古拉组下段；4.下石炭统包古图组；5.下石炭统希贝库拉斯组；6.混杂岩；7.碱长花岗岩；8.二长花岗岩；9.断层；10.接触热变质带；11.地质界线
Fig. 10. Three-dimension configuration and three-dimensional shape of the pluton
表 1 后造山伸展型花岗岩岩体与围岩接触面产状深部延展的宏观综合判断标志
Table 1. The macro-comprehensive judgment sign of deep extension of the contact boundary between post-collisiongranite and country rock
判断标志 对称型 不对称型 浅剥露 中等剥露 深剥露 浅剥露 中等剥露 深剥露 接触面产状 缓外倾 陡倾 内倾 一侧外倾，一侧陡倾 一侧外倾，一侧陡倾 一侧内倾，一侧陡倾 围岩岩脉发育程度 发育 少量发育 不发育 不对称发育 一侧较发育 一侧少量发育 接触变质带宽度 宽 较宽 窄，变质程度高 不对称，一侧较宽 一侧较宽 窄，变质程度高 顶垂体发育程度 常见 不发育 不发育 一侧常见 不发育 不发育 围岩包体发育程度 多 较少 少 一侧较多 一侧较发育 少 相带界线清晰程度 明显 较明显 不明显 明显 一侧明显 不明显 
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