论文部分内容阅读
通过对辽西阜新地区中侏罗世蓝旗组火山岩的岩石地球化学研究,燕山地区存在着中侏罗世高Sr低Y型火山岩。这些高Sr低Y型火山岩为高铝高钠低镁(Al2O3>15％,Na2O≥3.37％,MgO≤1.33％,Mg＃≤0.35)的安山岩-英安岩,高Sr(≥541μg/g)低Y、Yb(Y≤19μg/g,Yb≤1.35μg/g)含量及高Sr/Y(≥40)比值,强烈的稀土元素分馏((La/Yb)N>17,(No/Yb)N>1.2)),Eu异常不明显(0.82～0.96),高场强元素(如Nb、Ta)相对亏损。这些特征与太古代英云闪长岩-奥长花岗岩-花岗闪长岩(TTG)岩套相似。我们认为这些火山岩起源于古老的下地壳玄武质岩石的部分熔融,其形成可能与玄武质岩浆的底侵作用有关。辽西中侏罗世蓝旗组高Sr低Y型火山岩对探讨燕山造山带岩浆起源及地球动力学具有重要意义。
Based on the lithogeochemical study of the Mid-Jurassic Blue Flag volcanic rocks in Fuxin area, western Liaoning, Yanshan area is characterized by high-Sr low-Y volcanic rocks of Middle Jurassic. These high Sr low-Y volcanic rocks are andesite-dacite with high aluminum, high sodium and low magnesium (Al2O3> 15%, Na2O≥3.37%, MgO≤1.33%, Mg # ≤0.35) (La / Yb) N> 17, (No / Yb), low Y, Yb (Y≤19μg / g, Yb≤1.35μg / g) and high Sr / N> 1.2), Eu anomalies are not obvious (0.82 ~ 0.96), high field strength elements (such as Nb, Ta) relative loss. These features are similar to those of the Archaean epoch-diorite-olivine-granodiorite (TTG). We believe that these volcanic rocks originated from the partial melting of the ancient lower crust basaltic rocks and their formation may be related to the underplating of basaltic magmas. The high-Sr low-Y volcanic rocks of the Mid-Jurassic Lanqi Formation in western Liaoning Province are of great significance in exploring the origin and geodynamics of the Yanshan orogenic belt.