An experimental study of shear deformation and mineral composition changes of granite under the condition of high temperature and high pressure
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摘要:
在构造变形过程中，流体控制成矿作用的机制是目前世界矿床界共同面临的问题之一。通过研究剪切变形过程中的力学-化学作用，理解剪切构造应力和流体在构造成岩成矿过程中的行为与作用是解决这一科学问题的关键环节。在花岗岩高温高压剪切变形实验的基础上，分析了实验变形的矿物反应特征及矿物反应引起的化学成分变化，讨论了矿物反应与变形的相互影响。实验结果表明，变形样品中斜长石、钾长石和辉石以脆性-塑性变形为主，石英和云母以塑性变形为主。同时流体与岩石的相互作用引起了矿物间的反应，其中钾长石、辉石发生水解作用最典型。实验变形整体受应变局部化控制，随着剪切变形加强，脆性破裂逐渐形成和发展为裂隙，应力不断释放，有金属元素沿裂隙充填，这些微观特征在实验样品中普遍存在，类似野外中的矿脉。本次实验为韧性剪切带的流变行为、化学行为和剪切作用过程提供了实验数据。
Abstract:The fluid-controlling mineralization mechanism during tectonic deformation is a worldwide research focus.In order to comprehend the behavior and role of shear tectonic stress and fluids in the process of tectonic diagenesis and mineralization, it is the key to study the mechanical-chemical effects in the shear deformation process.In this study, the authors analyzed the distribution of mineral reaction and the change of chemical composition caused by the mineral reaction in experimental deformed granite samples under the condition of high temperature and high pressure and discussed interaction between mineral reactions and deformation.The results indicate that plagioclase, k-feldspar and pyroxene can endure brittle-plastic deformation, while most of the quartz and mica display plastic deformation.The hydrolysis of K-feldspar and pyroxene due to the fluid-rock interaction is the most characteristic reaction in the minerals.The strain localization dominantly controls the overall deformation in the experiment.With the strengthening of shear deformation, the brittle fracture gradually forms and develops into cracks.Thus the stress is released, and metal elements are filled along the cracks.These microscopic characteristics are common in the experimental samples, similar to features of the vein in the field.This experiment provides experimental data for the rheological behavior, chemical behavior and shearing process of the ductile shear zone.
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图 2 实验装样设计
a—剪切变形后实验样品中的玄武岩熔体与橄榄岩产生了分离；b—实验装样结构图(实验压缩方向与预制断层带内的花岗岩样品呈45°, 围岩采用辉长岩样品)
Figure 2. Design of experimental sample
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图 3 实验样品花岗岩和辉长岩的微观结构(扫描电镜照片)
Bi—黑云母；Hb—角闪石；Kf—钾长石；Pl—斜长石；Mt—磁铁矿；Px—辉石
Figure 3. Microstructure of granite and gabbro samples(SEM)
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图版 Ⅰ
实验变形后样品的变形特征(扫描电镜照片):a.斜长石和钾长石矿物内的微破裂；b.辉石碎裂；c、d.钾长石剪切拉长形成条带；e.辉石边缘塑性变形, 与斜长石反应形成的反应边；f.云母塑性变形被拉长为条带。Bi—黑云母；Q—石英；Kf—钾长石；Pl—斜长石；Px—辉石
图版 Ⅰ.
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图 5 实验变形样品中黑云母与辉石脱水反应和熔体的分布特征(扫描电镜照片)
a—辉石和钾长石的矿物水解反应, 生成针柱状矿物；b—钾长石和黑云母的塑性变形；c—钾长石和斜长石的分解反应边, 矿物颗粒之间生成针状矿物；d—黑云母条带中呈现暗色矿物富集, 辉石发生水解作用。Bi—黑云母；Q—石英；Kf—钾长石；Pl—斜长石；Px—辉石
Figure 5. The dehydration reaction of biotite and pyroxene in deformed samples and distribution of melt under scanning electron microscopy(SEM)
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图版 Ⅱ
a~f.钾长石高温分解后熔体成分分布图(实验样品S17-4中典型矿物成分的面扫描图, 颜色明亮的代表矿物成分富集, 颜色暗的代表矿物成分亏损, 其中高Si、Al、K矿物呈现富集, 尤其是局部出现Al、K出现条带状富集)
图版 Ⅱ.
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图版 Ⅲ
a~i.实验样品S17-9中典型矿物成分的面扫描图(颜色明亮的代表矿物成分富集, 颜色暗的代表矿物成分亏损, 其中Si、Al、Na、Ca相对亏损, Mg、K、Fe、Ti相对富集形成熔体条带)
图版 Ⅲ.
表 1 实验条件与力学参数
Table 1 Experimental conditions and mechanicaldata of samples
样品号 T1/℃ T2/℃ 压力/
MPa差应力
/MPa应变速
率/s-1实验
时间/h应变量
/%S17-1 800 800 800 243.19 1×10-6 85 14.5 S17-2 800 800 800 202.13 1×10-7 104 31.2 S17-3 800 800 800 164.53 1×10-6 98 33.1 S17-4 800 800 800 240.88 1×10-7 82 17.8 S17-5 800 800 1000 190.94 1×10-6 108 14.8 S17-7 800 720 1000 270.15 1×10-7 139 15.1 S17-9 850 850 1000 / 1×10-7 80 21.2 S17-10 700 705 1000 231.49 1×10-6 121 23.7 S17-11 800 800 1000 281.23 1×10-7 166 9.1 注：T1为主控热偶温度；T2为副控热偶温度；主控热偶是控制实验温度的热偶, 而副控热偶主要是监控温度。实验的最后温度是主控热偶所显示的温度 
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