中文摘要：

为探讨北大巴山紫阳地区正长斑岩岩墙群的侵入年龄及其地质意义,对正长斑岩进行了锆石SHRIMP U-Pb年龄、主量元素及微量元素测定。结果显示,正长斑岩岩墙（脉）锆石SHRIMP U-Pb年龄为（432±5.8）Ma,为早志留世。正长斑岩的Si O2含量为59.62%~64.30%,岩石全碱含量为10.13%~12.11%,里特曼指数σ为5.10~8.64,为碱性系列;铝饱和指数（A/CNK）为0.88~1.08,具有准铝质特征。稀土元素总量为120.71×10-6~421.00×10-6,（La/Yb）N为17.50~34.36,显示为轻稀土富集、重稀土亏损的右倾型稀土配分模式;δEu为0.94~1.15,平均1.05,轻微的Eu正异常。微量元素具有既富集大离子亲石元素Cs、Ba,又富集高场强元素Nb、Ta、Zr、Hf的特点,Sr强烈亏损。研究结果表明,正长斑岩属于A型岩套中Al型亚类,其形成于大陆板内伸展构造背景下的裂谷环境中,具有地幔来源并受下地壳物质混染的特征。

英文摘要：

In order to explore the forming age and geological significance of the syenite porphyry dike swarms in the Ziyang area of the Northern Daba Mountains,the SHRIMP zircon U-Pb dating and analysis of major and trace elements of the syenite porphyry have been carried out in this paper.The SHRIMP zircon U-Pb dating shows that the syenite porphyry dike swarms were formed at 432 ± 5.8 Ma in Early Silurian.The syenite porphyry belongs to metaluminous and alkaline series with Si O2 contents of 59.62% ~ 64.30%,alkali contents of 10.13% ~ 12.11%,Rittmann Indexes of 5.10-8.64,and Aluminum Saturation Indexes of 0.88-1.8.Its Σ REE contents range from 120.71 × 10-6to 421.00 × 10-6,with（La/Yb）Nvalues ranging from 17.50 to 34.36,weak positive Eu anomalies（δEu = 0.94-1.15,average in 1.05）,and the feature of relative LREE enrichment and HREE depletion in the right-declined REE distribution patterns.Comparing to the primitive mantle values,it is characterized with the enrichment of LILEs（such as Cs,Ba） and HFSE（especially Nb,Ta,Zr,and Hf） and the strong depletion of Sr.The systemically geochemical research demonstrates that the syenite porphyry belongs to the A1 subgroup of the A-type igneous suites.It was formed in a tectonic rift environment in the continental intraplate extension setting by magmas mainly derived from the mantle with the contamination of the Lower crustal material.