燕山运动“绪动/A幕”的本意及其锆石U-Pb年代学制约  

Initiation,the First Stage of the Yanshan(Yenshan) Movement in Western Hills,Constraints from Zircon U-Pb Dating

作　　者：李海龙[1] 张宏仁[1,2] 渠洪杰[1] 蔡向民[3] 王猛[4] 

机构地区：[1]中国地质科学院地质力学研究所,北京100081 [2]中华人民共和国国土资源部,北京100812 [3]北京市地质调查研究院,北京102206 [4]中国五矿集团公司五矿勘查开发有限公司,北京100044

出　　处：《地质论评》2014年第5期1026-1042,共17页Geological Review

基　　金：中国地质调查局地质调查项目(编号1212010911063、1212011121095)的成果

摘　　要："燕山运动"提出已有90余年。该概念从产生之日到现在一直存在着巨大争论。本文首先回顾了该概念的原始含义及其存在的逻辑问题。翁文灏将燕山运动分为三个阶段:"绪动"阶段、即A幕;火山幕、或称为中间幕;B幕。"绪动/A幕"的本意指上火山岩系下部砾岩与煤系地层之间的不整合事件。需强调翁文灏所谓的上火山岩系包括了主体的火山岩和火山岩之下的砾岩。这套砾岩在辽西为海房沟组、在北京西山为龙门—九龙山组。翁文灏认为砾岩产生于燕山运动的"绪动/A幕",但"绪动/A幕"与"火山幕"的关系翁文灏认为难以阐述清楚。翁文灏在提出燕山运动(Yenshan movement)之后、丁文江提出了燕山期运动(Yenshanian movement)的名词。后续的研究者多因循"燕山期运动"的思想,但在中文表述中几乎只使用"燕山运动"的文字表述,这造成了逻辑上理解的差异,二者显然是不同的概念范畴,需予以区分。理清原始概念之后,本文通过位于北京西山雁翅镇田村、淤白村附近的钻孔和探槽,揭露出北京西山九龙山组底部的一套厚约12m火山凝灰岩。凝灰岩之下发育一套砾径可达2m、碳酸岩质的砾岩,与其下寒武纪地层呈不整合接触,代表"绪动/A幕"的不整合面。凝灰岩的锆石LA-ICP-MS U-Pb年代学测试揭示了154Ma和161Ma两期年龄,前者限定了九龙山组的底界年龄,后者可能代表了"绪动/A幕"发生的最早火山响应。最后本文依据不整合面穿时性特点指出位于龙门—九龙山组砾岩之下的不整合面在空间上应收敛于髫髻山组火山岩之下的不整合面。而龙门—九龙山组砾岩与髫髻山组火山岩具有同时异相的空间特征。The concept of ＂Yanshan movement＂ （＂ Yenshan movement＂） had been put forward by Professor Wong W H for more than 90 years.Endless debating exists after the concept was put forward.This paper reviewed the concept and corresponding logical questions firstly.Mr.Wong divided the movement into three stages：the A （the beginning）,the middle （the volcanicism） and the B stage.The unconformity of the A stage exists between the upper volcano rock series and the coal measure strata.Bottom of the upper volcano rock series is a suit of conglomerate,for example,the Longmen—Jiulongshan Formation in western Hills,Beijing,and the Haifanggou Formation in Liaoning province.Mr.Wong attributed the conglomerate to the A stage.A question puzzled by Wong W H was the temperal and spacial relationship between the conglomerate and the volcanics.This is an important issue,but frequently escaped the attention by followings.Wong W H did not distinguish the difference between the concept of ＂ Yenshan movement＂ （＂ Yanshan movement＂） and the ＂ Yenshanian movement＂ （＂ Yanshanian movement＂）,which leads to misunderstandings in following studying.After clarifying the original concept,through a drilling and an exploratory trench in Yanchi town,Mentougou county,Western Hills,this paper firstly discovered a suit of turf in 12m thick under the Jiulongshan Formation.Under the tuff,a suit of calcareous conglomerate in 2m particle size is unconformity with the Cambrian strata,which is just the unconformity of beginning of Yanshan movement.U-Pb dating of the tuff yield the eruption age of 154Ma and the inherited age of 161Ma.The former represents the maximum age of the Jiulongshan Formation and the later responses to the earliest volcanic eruption of the A stage in Western Hills,Beijing.Finally,this paper points out that the diachronism of the three unconformities in Western Hills.The unconformity under the Jiulongshan Formation and the Longmen Formation will converge to the main unconformity under the Tiaojish

关 键 词：燕山运动 绪动 上火山岩系 煤系地层 不整合面 钻孔揭示 

分 类 号：P542[天文地球—构造地质学] P597.3[天文地球—地质学]