北京十三陵-西山髫髻山组火山岩年龄及其地质意义  

SHRIMP and LA-ICP-MS U-Pb Ages and Geological Significance of the Volcanic Rocks in the Tiaojishan Formation in Ming Tombs Area ——Western Hills,Beijing

作　　者：于海飞[1] 张志诚[1] 帅歌伟 陈彦[1] 汤文豪[1] 

机构地区：[1]北京大学造山带与地壳演化教育部重点实验室北京大学地球与空间科学学院,北京100871

出　　处：《地质论评》2016年第4期807-826,共20页Geological Review

基　　金：部属高校国家大学生校外实践教育基地资助项目;国家重点基础研究发展计划(2013CB429801)项目的成果~~

摘　　要：北京西北部地区分布着大量的火山岩，对北京西山大台和十三陵地区的髫髻山组火山岩分别进行了SHRIMP锆石U-Pb和LA-ICP-MS定年，并对十三陵地区的髫髻山组火山岩进行了地球化学研究。结果表明，十三陵地区的髫髻山组火山岩地球化学特征和北京西山髫髻山组火山岩具有相似性。火山岩地球化学特征表现为高Al2O3、CaO、Na2O，低TiO2和MgO，在TAS图中落入粗安岩和英安岩区域，REE分馏明显，LREE富集，HREE亏损，Eu异常不明显，富集大离子亲石元素K、Sr、Ba，亏损高场强元素Nb、Ta、Ti，高的Sr/Y比值，同时Yb和Y的含量较低。在大台地区，分别获得了髫髻山组火山岩底部角砾岩和中部安山岩的SHRIMP 锆石U Pb年龄为152.1±1.9Ma、149±2Ma，侵入到髫髻山组下覆九龙山组地层中一闪长岩岩床年龄为149±3.2Ma；在十三陵地区，分别获得了髫髻山组底部凝灰岩、中部火山角砾岩和上部安山岩的LA-ICP-MS 锆石U-Pb年龄分别为157.2±1.2Ma、155.2±1.7Ma、153.1±2.2Ma。结合前人研究，十三陵地区髫髻山组火山时代为157～153Ma，大台地区髫髻山组火山活动时间为152～137Ma，十三陵地区的火山活动时间要稍早于北京西山大台地区。大台地区和十三陵地区地球化学、地质年代学及区域地质特征表明，北京西山和十三陵地区喷发时间的差异是由于燕山运动所形成不整合面的穿时性导致的，位于髫髻山组之下的不整合是一个主不整合面。The Western Hills and Ming Tombs （Shisanling） area in Beijing is characterized by extensively distributed Mesozoic volcanic rocks of the Tiaojishan Formation. In recent years, numbers of isotopic ages of volcanic rocks in Tiaojishan Formation have been obtained, however, they have a significant difference. The Western Hills can be divided into three sections, Ming Tombs area can be divided into four sections, systematic sampling were carried out in a typical cross section of the Tiaojishan Formation and were measured by LA ICP MS and SHRIMP zircon U Pb dating, respectively.Methods：The SHRIMP and LA ICP MS U Pb dating and whole rock geochemical analysis are employed to reveal the formation age and temporal as well as spatial characteristics of the Tiaojishan Formation.Results：By the geochemical analysis, the volcanic rocks in the Tiaojishan Formation in Ming Tombs area has a high Al2O3, CaO, Na2O, low TiO2 and MgO, fall into trachyandesite and dacite field in TAS diagram with enrichment of LREE and LILE （ K,Sr,Ba） and depletion of HREE and HFSE （ Nb,Ta,Ti）, moreover, these intermediate—acidic rock has a high Sr/Y ratio, while the levels of Yb and Y is low. Combined with previous research results, the geochemical characteristics of the volcanic in Ming Tombs area is similar to the volcanic rocks in Westen Hills. By systematical sampling, the writers obtained the following isotopic ages：the age range of the Tiaojishan Formation in Western Hills is 152~ 137 Ma, and the age range of the Tiaojishan Formation in Ming Tombs area is 157~153Ma. Combined with the dating results of previous researchers, the volcano startup time in the Ming Tombs area is earlier than that in the Western Hills. Conclusions：the diachronism of unconformity gives rise to the differences in the age of Tiaojishan Formation between Ming Tombs and Western Hills. Meanwhile, the unconformity under the Tiaojishan Formation is a primary unconformity in Beijing.

关 键 词：北京西山 十三陵 髫髻山组 燕山运动 不整合面 穿时性 

分 类 号：P588.14[天文地球—岩石学]