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| 北京燕山地区薛家石梁杂岩体特征、成因、源区性质及岩石圈减薄方式 | |
| 引用本文： | 苏尚国,邓晋福,赵国春,赵兴国,刘翠.北京燕山地区薛家石梁杂岩体特征、成因、源区性质及岩石圈减薄方式[J].地学前缘,2006,13(2):148-157. |
| 作者姓名： | 苏尚国 邓晋福 赵国春 赵兴国 刘翠 |
| 作者单位： | 1. 中国地质大学,地质过程与矿产资源国家重点实验室,北京,100083 2. 中国地质大学,岩石圈构造、深部过程及探测技术教育部重点实验室,北京,100083 3. 中国地质大学(北京)地球科学与资源学院,北京,100083 |
| 基金项目： | 国家高技术研究发展计划(863计划);中国科学院资助项目;科技部中国-斯洛伐克国际科技协作资助项目 |
| 摘 要： | 薛家石梁杂岩体位于北京北山地区,在平面上呈北西向的椭圆状,主要由辉长岩、二长辉长岩、二长岩、正长岩和花岗岩组成。根据锆石SHRI MP定年结果为132·8~123·3Ma,形成于早白垩世早期。野外地质特征、矿物学特征、岩石学特征及地球化学特征表明,薛家石梁杂岩体中二长岩是二长辉长岩岩浆与正长岩岩浆混合作用的产物,从辉长岩岩浆到二长辉长岩岩浆经历了结晶分异作用。薛家石梁杂岩体中正长岩具高Sr,低Y及Eu正异常特征,推测其可能来源于加厚陆壳的底部。薛家石梁杂岩体中辉长岩中Mg#值为65,w(Nb)/w(U)值为37·8,这些特征暗示其可能为原生岩浆。辉长岩中ε(Nd)值为-6·5,表明其源区岩石不具亏损地幔特征;而辉长岩具富集Pb、Ti、Nb正异常,Hf的负异常,与EMI型富集地幔特征(具Nb、Hf正异常及Pb的负异常)不一致;辉长岩中Rb、Th、Nb、U、La、Ce元素含量比EMI型富集地幔低一个数量级;杂岩体中N(87Sr)/N(86Sr)与N(206Pb)/N(204Pb)值具正相关关系也表明不具交代富集型地幔特征。因此,我们认为辉长岩岩浆源区应为软流圈地幔,而不是富集型地幔(EMI)。辉长岩中ε(Nd)的负值是辉长岩岩浆与太古宙下地壳相互作用的结果。因此,我们认为中国东部岩石圈减薄的主要机制是岩石圈的拆沉作用。 |
| 关 键 词： | 北京燕山地区 薛家石梁杂岩体 源区性质 岩石圈减薄方式 |
| 文章编号： | 1005-2321（2006）02-0148-10 |
| 收稿时间： | 2005-11-29 |
| 修稿时间： | 2006-01-09 |
Characteristics, origin and resource property of Xuejiashiliang complex, Beijing area and their relationship with the way of lithospheric thinning |
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| SU Shang-guo,DENG Jin-fu,ZHAO Guo-chun,ZHAO Xin-guo,LIU Cui.Characteristics, origin and resource property of Xuejiashiliang complex, Beijing area and their relationship with the way of lithospheric thinning[J].Earth Science Frontiers,2006,13(2):148-157. | |
| Authors: | SU Shang-guo DENG Jin-fu ZHAO Guo-chun ZHAO Xin-guo LIU Cui |
| Institution: | 1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China; 2. Key Laboratory of Lithosphere Tectonics and Lithoprobing Technology of Ministry of Education, China University of Geosciences, Beijing 100083, China; 3. School of Earth Science and Mineral Resources, China University of Geosciences, Beijing 100083, China |
| Abstract: | The Xuejiashiliang complex of the northern hills of Beijing is an oval igneous complex with a northwest trend in the Yanshan orogenic belt. It consists of gabbro, monzogabbro, monzonite, syenite and granite members. SHRIMP zircon dating results show that the age of Xuejiashiliang complex is 128.8～123.7 Ma, and thus formed in the early stage of the early Cretaceous (K~1_1). Geological, petrological, geochemical and Sr, Nd and Pb isotopic charateristics indicate that the monzonite member is a mixing product of monzogabbro and syenite magmas. The Mg~~~# value of Xuejiashiliang gabbro is 65, and its Nb/U value is 37.8. These values lead us to infer that the gabbro represents the primary magma. The -6.5 ε (Nd) value of gabbro shows no characteristic of depleted mantle. It occurs Pb, Ti positive anomalies and Hf negative anomalies, all of which are different from the characteristics of enriched mantle I (EMI) with Nb, Hf positive anomalies and Pb, Ti negative anomalies. The content of Rb,Th,Nb,U,La,Ce in gabbro are less than that in EMI. The ~ 87 Sr/~ 86 Sr and ~ 206 Pb/~ 204 Pb of the Xuejiashiliang complex are positively correlated, which are different from those of the EMI mantle. Therefore, we think that the source of the gabbro melts was the asthenosphere. The negative ε (Nd) value of gabbro resulted from the mixing of asthenosphere magma and the melting of Archean lower crust. We believe that thinning of the Mesozoic lithosphere in eastern China was the result of delamination. Accordingly the formation of the Xuejiashiliang complex went through the following stages. With the detachment of lithosphere in the early Cretaceous, volumes of mantle-derived gabbroic magma underplated the continental crust and induced partial melting of the lower crust. This, in turn, led to production of syenite magma. During cooling of the gabbro magma, fractional crystallization led to the formation of monzogabbro magma. Monzonite was formed by the mixing of monzogabbro and syenite magmas. The granite of the complex was produced by partial melting of upper crustal protoliths. |
| Keywords: | Yanshan area of Beijing Xuejiashiliang complex characteristics of sources the way of lithospheric thinning |
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