满洲里地区巴勒根哈德古火山口的发现及区域构造背景研究  

Discovery of Balegehade Ancient Crater in Manchurian and the Research of It's Regional Tectonic Setting

作　　者：任升莲[1] 宋传中[1] 李加好[1] 宫龙[1] 黄鹏[1] 林寿发[1,2] 李龙明[1] 杨帆[1] 刘乐[1] 胡达[1] 刘国厅[1] 

机构地区：[1]合肥工业大学资源与环境工程学院,中国合肥230009 [2]加拿大滑铁卢大学

出　　处：《地质论评》2015年第6期1257-1269,共13页Geological Review

基　　金：中国地质调查局项目(编号:1212011121081)的成果

摘　　要：满洲里地区位于额尔古纳成矿带南段,深受古亚洲构造域和太平洋构造域的影响。在中生代产生了具有很大影响的构造——岩浆活动。2011年在进行国家地质调查项目时,首次在内蒙古新巴尔虎右旗西北约42 km处发现一个被第四系掩盖的古火山口,称为巴勒根哈德古火山口,地理坐标为东经116°20.6096’,北纬48°51.4327’。在遥感影像图上表现为与之相对应的环形构造和放射状水系,非常清晰地显示出环状火山口。岩性主要由流纹质火山角砾熔岩、火山集块熔岩、火山集块角砾熔岩与流纹岩组成,构成数个韵律层。除顶底不完整以外,可见三个完整的喷发韵律层,均由爆发相开始,以溢流相结束,爆发指数为0.72~0.92,自下而上喷发力度逐渐减弱。流纹岩中锆石U-Pb测年获得其年龄为167.8±3.3~162.2±2.1 Ma,指示该火山喷发的时代为中侏罗世。应力场分析研究认为本地区在中生代早期σ1为NWW向,稍后转为NNW向,说明中生代以后本地区应力场由古亚洲体制转为太平洋构造体制。由于叠加了NNW方向的挤压作用,导致得尔布干断裂带活化,并形成了NNE向具有左旋剪切性质的额尔古纳断裂带以及与之配套的NWW向的张性断裂,二者的交切处成为中侏罗世中酸性岩浆上升和就位的最佳空间。因此,在NNE向上常形成串珠状分布的中心式火山口群,巴勒根哈德和甲乌拉火山口就是其中的两个,它们是古亚洲构造和太平洋构造背景共同作用下的产物。Manchuria region is located in the southern section of the Ergun block,which was heavily influenced by Pal-Asia and Pacific tectonic domain causing large scale of magmation and tectonic activities in Mesozoic. An ancient crater with geographical coordinates of longitude 116° 20. 6096' and latitude 48° 51. 4327' is first discovered at about 42 km northwest of New Barg Right Flag in Inner Mongolia during the national geological survey project in 2011. This ancient crater is covered by the Quaternary sediments and named as Balegenhade ancient crater. Circular structures and radial drainage in images of remote sensing very clearly show the cyclic volcanic necks. The lithology is mainly composed of rhyolitic volcanic breccia lava,volcanic agglomerate lava,volcanic agglomerate breccia lava and rhyolite forming several cyclothems. Three complete eruption circulations starting from explosive facies ending with overflow facies can be observed except that the top and bottom are incomplete. The explosive index is from 0. 72 to 0. 92 experiencing a gradual weakening process from below to above. Zircon U-Pb age in rhyolite ranges between 167. 8 Ma ± 3. 3 ~ 162. 2 ± 2. 1 Ma that indicates the eruptive activities took place in Middle Jurassic. The analysis of stress field shows that the direction of σ1 converted from NWW to NNW since early mesozoic to later,which reveals a tectonic transformation from ancient Asia to Pacific. The Buergan fault zone reactivated under the compressive force of NWW——SEE direction,then formed the NNE-trending Eerguna fault zone with the property of sinistral shearing and corresponding NWW-trending tensile fractures,so the conjunctions of those two sorts of faults would be the ideal space for rising magma. Therefore,those many centric craters including Balegenhade and Jiawula craters distributed like beads on NNE direction are results of the joint effect of ancient Asia tectonic and Pacific tectonic.

关 键 词：满洲里 火山口 流纹岩 火山角砾岩 太平洋构造域 中生代构造—岩浆活动 

分 类 号：P548[天文地球—构造地质学]