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研究区红石泉位于龙首山成矿带西部,本次研究对区内正长岩进行系统的元素地球化学和年代学分析测试,理清其岩石成因,探讨其构造意义.结果 显示,红石泉正长岩样品的w(SiO2)为57.15％～65.03％,w(Al2O3)为14.31％～18.46％,相对高钾w(K2O)=4.55％～11.30％和富碱w(K2O+ Na2O)=10.48％～13.10％,K2O/Na2O比值为0.64～4.22,可归类为准铝质高钾碱性系列.岩石相对富集Rb,Th等大离子亲石元素与轻稀土,相对亏损Nb,Ta,P和Ti等高场强元素与重稀土,Eu(均值0.66)呈轻微负异常.锆石U-Pb定年指示其结晶年龄为416.00±0.17 Ma(MSWD=0.88).综合分析认为,红石泉正长岩的形成与壳幔岩浆混合作用密切相关.晚志留纪至早泥盆纪时,祁连—柴达木板块和阿拉善板块的碰撞造山作用进入后碰撞伸展阶段,地幔岩浆的底侵作用诱发了地壳熔融,从而形成壳源岩浆,而幔源岩浆与壳源岩浆的混合作用形成了红石泉正长岩的母岩浆. 相似文献
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Taiji Chida Yuichi Niibori Osamu Tochiyama Hitoshi Mimura Koichi Tanaka 《Applied Geochemistry》2007,22(12):2810-2816
Cementitious materials used for radioactive waste repository construction complicate the performance assessment of radioactive waste systems because the use of cement may greatly alter the pH (8–13) of groundwater and release constituents such as calcium ions. Under such conditions, it is important to clarify also the dynamic behavior of silica (silicic acid), in order to evaluate the alteration in the chemical and physical properties of the fractured layer or the host rock surrounding the repository. Since silica undergoes polymerization, precipitation or dissolution depending on the pH and/or temperature, the behavior of silica would be greatly complicated in the presence of other ions. This study is focused on the deposition rates of polysilicic acid and soluble silicic acid with up to 10−3 M Ca ions. In the experiment, Na2SiO3 solution (250 mL, pH > 10, 298 K) was poured into a polyethylene vessel containing amorphous silica powder (0.5 g), and a buffer solution, HNO3, and CaNO3 as Ca ions were sequentially added into the vessel. The pH of the solution was set to 8. The silica, initially in a soluble form at pH > 10 (1.4 × 10−2 M), became supersaturated and either deposited on the solid surface or changed into the polymeric form. Then the concentrations of both poly- and soluble silicic acid were monitored over a 40-day period. The decrease of polysilicic acid became slow with an increase in the concentration of Ca ions in the range of up to 10−3 M. In general, the addition of electrolytes to a supersaturated solution accelerates the aggregation and precipitation of polymeric species. However, the experimental result showed that polysilicic acid in the presence of Ca ions is apparently stable in solution, compared with that under a Ca-free condition. On the other hand, the concentration of soluble silicic acid in the presence of Ca ions immediately became metastable, that is, slightly higher than the solubility of soluble silicic acid. Its dynamic behavior was similar to that in the Ca-free condition. 相似文献
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