北淮阳东段同兴寺碱性岩体地球化学特征、LA-ICP-MS锆石U-Pb年龄及其地质意义  

Geochemical Characteristics and LA-ICP-MS Zircon U-Pb Geochronology of the Tongxingsi Alkaline Intrusion in the Eastern North Huaiyang and Their Geological Significance

作　　者：彭智[1] 杜建国[1] 陈芳[1] 邱军强[1] 万秋[1] 董婷婷[1] 汤金来[1] 

机构地区：[1]安徽省地质调查院,合肥230001

出　　处：《地质学报》2015年第4期701-714,共14页Acta Geologica Sinica

基　　金：中国地质调查局地质调查工作项目(编号1212011220547)资助的成果

摘　　要：同兴寺岩体为北淮阳构造带内著名的碱性岩体。同兴寺碱性岩具SiO2、Al2O3含量中等,富碱、准铝质、Mg#小等特征。富集大离子亲石元素Rb、Ba、Sr,亏损高场强元素Ta、Ti。LaN/YbN与LREE/HREE比值均较大,具较弱的δCe负异常。稀土元素配分曲线表现为轻稀土分馏较明显,重稀土稍平坦,属轻稀土富集型。通过LA-ICP-MS锆石U-Pb定年,获得同兴寺二长闪长岩和角闪正长岩的锆石206 Pb/238 U年龄为126.1±1.1 Ma和124.4±1.3 Ma,均为同兴寺杂岩体早白垩世中期岩浆活动的产物。主、微量地球化学分析表明岩浆来源于地幔物质部分熔融,同时受到地壳物质的混染。基于前人关于该区区域地质背景方面的研究成果和本次地球化学构造环境判别方面的研究,认为同兴寺碱性岩形成于后碰撞的伸展环境。Tongxingsi rock is a famous alkaline intrusion in the North Huaiyang tectonic belt. Tongxingsi alkaline intrusion is characterized by medium contents of SiO2 and Al2O3, alkali rich, aluminum to-be, and low Mg#. It is rich in large ion lithophile elements such as Rb,Ba, Sr, and deplete in high field strength elements such as Ta and Ti. The ratio of LaN/YbN and LREE/HREE are all higher. It has weaker negative anomaly of 3Ce. It belongs to LREE rich type for its REE distribution patterns indicate the LREE is steep while the HREE is relatively flat. Tongxingsi monzodiorite and hornblende syenite were dated to be 126.1±1.1 Ma and 124.4±1.3 Ma, which indicates it belongs to the second magma activity products of Tongxingsi complex intrusion in the early Cretaceous. The major and trace element geochemical analyses indicate the magma came from partial melting of the mantle and contaminated by continent crust. Based on the integrated results of previous studies about regional geological background and geochemical tectonic environment discrimination of this study, the paper considers Tongxingsi alkaline intrusion formed at the post-collsional extension setting.

关 键 词：碱性岩 地球化学 LA-ICP-MS锆石U-PB测年 早白垩世 北淮阳 

分 类 号：P588.15[天文地球—岩石学] P597.3[天文地球—地质学]