论文部分内容阅读
义县组火山岩在辽西分布广泛,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,w(SiO2)=63.52%～65.94%,w(Na2O+K2O)=9.63%～10.15%,w(Na2O)/w(K2O)为0.96～1.08,属于高钾碱性岩系列,同时具有较低的w(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(1.46×10-6～4.15×10-6)、Co(19.8×10-6～45.9×10-6)和Ni(0.100×10-6～1.55×10-6)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。
The volcanic rocks of Yixian Formation are widely distributed in western Liaoning. The alkaline trachyte of the study area is located at the top of the Yixian Formation volcanic rocks in Jianchang area. Detailed geochronology and geochemical studies show that zircon U-Pb ages are (120.3 ± 1.5) Ma (SiO2) = 63.52% ~ 65.94%, w (Na2O + K2O) = 9.63% ~ 10.15%, w (Na2O) / w (K2O) is 0.96 ~ 1.08, (La / Yb) N = 8.96 ~ 12.02, with a lower w (MgO) (0.75% ~ 1.05%). The REE pattern is light REE enrichment. (ΔEu = 1.07 ~ 1.16), Cr (1.46 × 10-6 ~ 4.15 × 10-6), Co (19.8 × 10-6 ~ 45.9 × 10-6) and Ni (0.100 × 10-6 ~ 1.55 × 10-6) content is low. Trace elemental cobwebs showed significant positive Ba and Pb anomalies and negative Sr, Ti and Y anomalies. In addition, Zr and Hf showed some positive anomalies. It is considered that the alkaline rocks formed in a tensioned tectonic setting and the source depth is larger, which is the result of the crust-mantle interaction. The volcanic rocks in the study area are enriched mantle with intense crystallization of olivine, orthopyroxene and clinopyroxene Magmatic uplift invades the lower crust and undergoes assimilation and partial melting, which then erupts along the deep faults to the surface.