粗面玄武岩熔融-结晶过程中角闪石-熔体二面角:温度和压力的影响  

Amphibole-melt Dihedral Angle in the Process of Melt-crystallization of Trachybasalt:Effects of Temperature and Pressure

作　　者：赵东宇[1,2] 张波[1,2] 胡贤旭[1,2] 范大伟[1] 周文戈[1] 谢鸿森[1] 

机构地区：[1]中国科学院地球化学研究所地球内部物质高温高压院重点实验室,贵州贵阳550081 [2]中国科学院大学,北京100049

出　　处：《地球科学与环境学报》2016年第3期341-354,共14页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(41274105;41374107);中国科学院地球化学研究所青年创新科技人才培养计划项目(2013;范大伟);中国科学院B类战略性先导科技专项项目(XDB18010401)

摘　　要：矿物-熔体二面角是了解岩浆岩结构演化和岩浆动力学的重要参数。为了研究温度和压力对矿物-熔体二面角的影响,以粗面玄武岩为初始样品,在压力为0.6～2.6GPa,温度为800℃～900℃,恒温100h的条件下分别对初始样品进行了温度和压力两个系列的熔融-结晶试验。温度系列试验（3组）条件为：恒定压力为0.6GPa,首先在温度为1 350℃的条件下恒温1h,使粗面玄武岩完全熔融,然后改变温度使粗面玄武岩熔体分别在温度为800℃、850℃和900℃以及恒温100h的条件下结晶。压力系列试验（4组）条件为：分别在压力和温度为0.6GPa、1 350℃,1.1GPa、1 375℃,1.6GPa、1 400℃,2.1GPa、1 425℃和2.6GPa、1 450℃条件下恒温1h,使粗面玄武岩完全熔融,然后降温至900℃,恒温100h使粗面玄武岩熔体结晶。在上述试验条件下,粗面玄武岩熔体主要结晶相为角闪石。采用在二维任意切面测定二面角的方法得到试验产物中的角闪石-熔体二面角。将试验获得的角闪石-熔体视二面角的累积频率与理论频率累积曲线进行对比,并讨论了温度和压力对二面角的影响。角闪石-熔体视二面角中值随着温度的升高而增加。这主要是由于在高温条件下,角闪石的成核密度小,生长速度快,有利于角闪石晶体的生长粗化,大的颗粒相互接触拼接形成高角度二面角,而在低温条件下,角闪石的成核密度大,生长速度慢,不利于角闪石晶体的粗化,角闪石的矿物颗粒较小且近平行排列,从而形成低角度二面角。另外,角闪石-熔体视二面角中值随着压力的升高先升高再降低,最后升高,这可能是熔体和矿物之间显著的力学性质差异造成的。试验结果证明,在岩浆结晶作用早期,随着矿物由孤立状态向拼接结构发展,矿物-熔体二面角逐渐增大。同时,将本次试验结果与前人关于岩浆结晶晚期矿物（或矿物-熔体）二面角的演化规律相结合The mineral-melt dihedral angle is a very important parameter to further understand thecrystallization kinetics and the textural evolution of magma.Using trachybasalt as the starting material,two series of melt-crystallization experiments（temperature series and pressure series）were conducted at the pressures of 0.6-2.6GPa,the temperatures of 800 ℃-900 ℃ and the annealing time of 100 h,to investigate the influence of temperature and pressure on the mineral-melt dihedral angle.In the temperature series（3groups）,trachybasalt were fused at the temperature of 1 350 ℃,the pressure of0.6GPa and the annealing time of 1h,to obtain homogeneous melts;then,the melting temperatures dropped to the crystallization temperatures of 800℃,850℃and 900℃,and annealed for 100 h.In the pressure series（4groups）,the trachybasalt were fused at the temperatures and pressures of 1 350℃and0.6GPa,1 375℃and 1.1GPa,1 400 ℃ and 1.6GPa,1 425 ℃ and 2.1GPa,and 1 450 ℃ and2.6GPa,respectively;the samples were kept under such conditions for 1hto ensure completely melting and proper homogeneity,and then the temperatures dropped to the crystallization temperature of 900℃and annealed for 100 h.Amphibole was the main crystal phase in the process of trachybasalt crystallization under the above experimental conditions.The amphibole-melt dihedral angles from the experimental products were obtained by measuring the dihedral angles in the two-dimensional random sections.The effects of temperature and pressure on the dihedral angle were discussed by comparing the observed cumulative frequency of the amphibole-melt dihedral angles in the run products with the theoretical cumulative frequency curve.The median of apparent dihedral angles in amphibole-melt increases with the increase of temperature.The nucleation density of amphibole is small while the growth rate is fast at high temperature;thus,the higher temperature is beneficial to the growth and coarsening of amphibole,so that the grains impinge and form the high dihedral ang

关 键 词：二面角 熔融-结晶 粗面玄武岩 高温高压 界面能 拼接结构 结构平衡 岩浆结构演化 

分 类 号：P589.1[天文地球—岩石学] P586[天文地球—地质学]