高温高压下花岗闪长质熔体结晶作用的实验研究

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	高温高压下花岗闪长质熔体结晶作用的实验研究
其他题名	Experimental study of crystallization in granodioritic melts at high temperature and high pressure
	夏伟奔
	2009-05-31
学位授予单位	中国科学院地球化学研究所
学位授予地点	地球化学研究所
学位名称	博士
关键词	角闪石黑云母斜长石结晶作用花岗闪长质熔体高温高压实验
摘要	岩浆的分离结晶作用是岩浆演化的重要过程，与许多火成岩石的形成密切相关。自二十世纪50年代以来，采用实验手段研究岩浆的形成、演化一直受到地质学家的高度重视。本文在0.5-2.0GPa、650-750℃和一定水含量条件下，以东准噶尔花岗闪长岩为初始物，进行了花岗闪长质岩浆结晶作用的实验研究。其结果可为东准噶尔地区A型花岗岩的成因提供一定的实验依据。通过对实验产物详细的岩相学观察和电子探针分析，获得以下主要认识：（1）熔体的含水量对矿物开始结晶的温度和晶出矿物的形状、颗粒大小有重要影响。相同时间内熔体含水量高时结晶出的矿物自形程度更好、粒度增大；随着熔体含水量的增加，斜长石的液相线温度降低；保持熔体含水量不变的情况下，随着压力的增加斜长石从熔体中结晶的温度降低。（2）在压力为0.5GPa、熔体水饱和的条件下，花岗闪长质熔体中斜长石在675℃时开始结晶。结晶的斜长石与原岩的斜长石相比，其成分相对富钠长石而贫钙长石。在温度和熔体水含量一定的条件下，从花岗闪长质熔体中晶出的斜长石随着压力的增加，其钙长石组分增加。（3）实验产物中的角闪石属于钙角闪石类，具体以普通角闪石为主。与初始花岗闪长岩的角闪石相比，实验产物的角闪石SiO2含量低，Fe3+很少。结晶形成的黑云母为铁叶云母，在2.0GPa压力时没有黑云母晶出而出现多硅白云母。（4）花岗闪长质熔体发生矿物结晶后的残余熔体的成分受温度、压力和含水量的变化而变化。残余熔体中SiO2含量随着矿物从熔体中结晶程度的增加而升高。与无斜长石结晶的情况相比，有斜长石结晶时残余熔体的SiO2含量要高。在Na2O+K2O-CaO、FeO/(FeO+MgO)分别与SiO2的协变图中，残余熔体成分均落入A型花岗岩区，反映了它们与A型花岗岩在主量元素组成上的近似。因此，本文的实验证明，东准噶尔地区的A型花岗岩浆可以通过花岗闪长质岩浆发生角闪石、黑云母、斜长石的分离结晶作用形成。
其他摘要	Fractional crystallization of magma is an important process during magma evolution, and has close connections with the formation of many igneous rocks. Since 1950's, experimental study on the origin and evolution of magmas has been receiving much attention from geologists. In this paper, crystallization experiments of the granodioritic melts at conditions of 0.5-2.0GPa, 650-750 C and water unsaturated or saturated are carried out. The starting material is the granodiorite collected from East Junggar. The results can provide experimental evidence for the origin of the A-type granites in East Junggar. After detailed petrographical observation and EPMA analysis for the run products, the following conclusions can be drawn: (1) The water content in the melt has great effect on the temperature that minerals start to crystallize, and on the shape and size of crystals. At the same duration, the minerals crystallizing from the melts with higher water content have better shape and larger size than those from the melts with lower water content. With the increase of water content, the liquidus temperature of plagioclase is lower. The crystallization temperature of plagioclase decreases as the pressure increases at the same water content. (2) At 0.5GPa and water saturated, the plagioclases begin to crystallize at 675C. Their composition is relatively rich in albite compared with the plagioclases in the starting granodiorite. The anorthite component in the plagioclases of experimental products increases as the pressure increases at the same water content and temperature. (3) The amphiboles in experimental products are calcic ones, mainly hornblendes. In comparison with the starting granodiorite, the experimental hornblendes have low SiO2 content and little Fe3+. The experimental biotites are siderophyllites, and at 2.0GPa, no biotites occur in the run products, instead phengites are observed. (4) The composition of the residual melt after crystallization of the granodioritic melts is changed with the variations of temperature, pressure and H2O content. With the increases of crystallinity, and the appearance of plagioclase, the SiO2 content of the residual melt increases. In the figures of Na2O+K2O-CaO, and FeO/(FeO+MgO) versus SiO2, all data points of the residual melts are plotted into the range of A-type granite, implying the similarity in the major compositions between the residual melts and A-type granites. Therefore, the experimental results suggest that the A-type granitic magma in East Junggar could be formed by fractional crystallization of hornblende, biotite, and plagioclase from granodioritic magma.
页数	40
语种	中文
文献类型	学位论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/3516
专题	研究生_研究生_学位论文
推荐引用方式 GB/T 7714	夏伟奔. 高温高压下花岗闪长质熔体结晶作用的实验研究[D]. 地球化学研究所. 中国科学院地球化学研究所,2009.

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