• 责任者：Li Wuping (School of Civil Engineering ; Guangzhou University ; Guangzhou 510006 ; China)
• 刊名：Earth Science
• 出版年：2013
• 卷期：38(6)
• 关键词：火山岩 ; volcanic rocks ; 岩石地球化学 ; lithogeochemistry ; 辽宁 ; Liaoning Province
• 页码：p.1153-1168
• 图表：7 illus., 2 tables, 76 refs.
• 分类号：0801
• issnNo：ISSN1000-2383
• isbnNo：CN42-1233/P

     The Middle Jurassic volcanic rocks of Haifanggou formation from the western Liaoning Province is an important component of Mesozoic volcanic rocks in the Yanshan Orogenic belt. The volcanic rocks of Haifanggou formation, which are mainly composed of traehyandesite with dacite and andesite, are metaluminous calc-alkaline and high-K series. Geochemical data indicate that the Middle Jurassic volcanic rocks of Haifanggou from the western Liaoning province have the low Mg adakitie volcanic features, such as SiO2≥51.98%, Al2O3 ≥15.0 %, MgO 〈4. 18% （Mg^#〈0. 48）, Sr≥436 X 10-6, Yb≤2. 25×10^-6, Y≤ 23. 14×10^-6, Cr≤81.09×10^-6, Ni≤34. 66×10^-6 , Y/Yb≤14. 25, Sr/Y≥39, and Nb/Ta≈20. The rocks are enriched in light rare earth elements （LREE）, Ba, U, Sr and Pb, and are depleted in heavy rare earth elements （HREE） and high field strength elements （such as Nb, Ta, Ti） ,and strongly fractionated （（La/Yb）N≥10. 37） with weak negative Eu anomaly or positive Eu anomaly （0. 79 to 1.05 in Eu/Eu^＊ ）. In addition, these adakitic volcanic rocks also have that low （^143 Nd/^144 Nd） initial ratios （0. 511 603 to o. 511 733, -15.84 to -13. 30 in epsilon end （t））, moderate （^87 Sr/^86 Sr） initial ratios （0. 704 9 to 0. 705 6, 8. 64 to 18. 11 in epsilon εSr （t）） and a higher depleted mantle model ages （1. 81 to 1. 99 Ga in TDM）, showing enriched mantle end-member （EMI） characteristics. These features indicate that Haifanggou adakitic magma were derived from the partial melting of a thickened eclogite from the lower crust, and its origin is related to underplating of the basaltic magma. Combining with geochemistry of Mesozoic volcanic rocks in Yanshan Orogenic belt, the Early-Middle Jurassic in the Yanshan orogenic belt is a conversion period from the ancient Asian Ocean tectonic system to the paleo-Pacific tectonic system, while the generation of the Middle Jurassic adakitic volcanic rocks of Haifanggou formation （174 Ma） shows that the Yanshan orogenic belt has come into ＊he evolution stage of the paleo-Pacific tectonic system. The research results can facilitate the understanding of the deep mechanism of Yanshan movement and lithospheric thinning process.