义县组火山岩在辽话分布广泛,研究区碱性粗面岩位于建昌地区义县组火山岩的顶部,详细的年代学及地球化学研究表明,锆石u—Pb年龄为(120.3±1.5)Ma,具有较高的SiO2:和碱含量,ω(SiO2)=63.52%~65.94%,ω(Na20+K2O)=9.63%一10.15%,ω(Na20)/ω(K20)为0.96~1.08,属于高钾碱性岩系列,同时具有较低的ω(MgO)(0.75%~1.05%),稀土配分模式为轻稀土富集,重稀土亏损的右倾型模式(La/Yb)n=8.96~12.02),较弱的正Eu异常(δEu=1.07—1.16),相容元素Cr(1.46×10^6~4.15X10^6)、c0(19.8X10^6。~45.9X10^6)和Ni(0.100x10^6~1.55×10^6)含量低。微量元素蛛网图显示明显的Ba和Pb正异常,以及Sr、Ti和Y负异常,此外,zr和Hf显示一定的正异常。认为碱性岩形成于拉张的构造环境,且来源深度较大,是壳幔相互作用的结果,研究区火山岩是经过强烈橄榄石、斜方辉石和单斜辉石结晶分异的富集地幔岩浆上升底侵至下地壳,并经历同化混染和部分熔融,然后沿着深大断裂喷发至地表。
Volcanic rocks are widespread in western Liaoning province. The studied alkaline trachytes are located at the top of the Yixian Formation volcanic rocks in Jianchang. Systemic studies on chronology and geochemistry indi- cate that the volcanic rocks were formed in 120.3 ± 1.5 Ma (zircon LA-ICP-MS U-Pb age). In addition, the volcan- ic rocks have relatively high Si02 (63.52% -65.94% ) and(Na20 + K20) (9. 63% - 10. 15% ), and Na20/K20 is between 0.96 and 1.08, with the feature of high-K alkaline magmas. In contrast, the volcanic rocks have lower MgO (0.75%-1.05%), Cr (1.46x10^6 -4. 15x106), Co(19.8x10^6 -45.9x106) and Ni (0.100 x10^6 -1. 55 x 10^6 ) contents. In the chondrite-normalized patterns and primitive-mantle normalized diagrams, the volcanic rocks