摘要
辽北清原地区英云闪长岩的岩石化学成分具有富SiO_2、Al_2O_3、Na_2O,Ba、Mg~#,LREE,而贫K_2O、Yb、Y、HREE的特点,显示奥长花岗岩演化趋势,并具有Adakite(埃达克岩)和新太古代富铝型TTG岩石特征。岩石∑REE偏低,稀土元素显示强烈分异,基本无Eu异常,Nb、Ta和Yi负异常,具有低的Nb/Ta、(La/Yb)N比值及其它微量元素特征,表明其与岛弧或大陆边缘弧玄武质岩石特征相似。岩石LA-ICP-MS锆石U-Pb同位素定年表明该岩石形成年龄为2 550.2±7.1 Ma,时代为新太古代。地球化学特征指示英云闪长岩可能是在较高温度和压力下由俯冲的含水玄武质洋壳部分熔融形成,残留相中有较多的角闪石和斜长石,较少的石榴石。辽北清原地区英云闪长岩的这种成因机制表明当时陆壳以水平方式增生,华北克拉通2.5 Ga左右可能存在微陆块碰撞拼合事件,碰撞拼合之前不同微陆块之间可能存在一个古大洋。
The rock chemical composition of the Tonalite in Qingyuan area of northern Liaoning province is rich in SiO2, Al2O3, Na2O, Ba, Mg, and LREE, but poor in K2O, Yb, Y, and HREE,which show the evolutionary trend of the orthogonal granite with Adakite(Adak Rock)and Neoarchean Al-rich TTG rock features.The ΣREE of rock is low, REE show strong differentiation, basically no anomalies of Eu, negative anomalies of Nb, Ta, and Yi, low Nb/Ta and(La/Yb)N ratios show that they are related to island arcs or basaltic rocks on the continental margin. The rock LA-ICP-MS zircon U-Pb isotopic dating indicates that the rock formation age is 2 550.2±7.1 Ma, which is in Neoarchean. The geochemical characteristics indicate that the Tonalite is likely to be partially formed by subduction of the submerged basaltic oceanic crust at higher temperatures and pressures. There are more amphibole and plagioclase in the residual phase, containing less garnet. The genesis mechanism of the Tonalite in the Qingyuan area of northern Liaoning Province indicates that the continental crust was proliferated horizontally at that time. Due to the existence of a microcontinent collision event around 2.5 Ga of the North China Craton, there may be one ancient ocean between the different microlandmass before the collision and consolidation.
作者
余超
YU Chao(Liaoning Institute of Geology and Mineral Resources Survey, Shenyang 110031, China)
出处
《地质调查与研究》
2019年第1期18-29,共12页
Geological Survey and Research
基金
中国地质调查局"辽宁1/5万夏家堡等四幅区域地质矿产调查项目(12120114028801)"
