内蒙古辉腾锡勒玛珥式火山口群特征与成因

Characteristics and genesis of Maar craters in Huitengxile, Inner Mongolia

在内蒙古乌兰察布市辉腾锡勒草原上分布着上百个负地形的玛珥式火山口。它们数量多、分布密集、保存好。它们的主要特征是所有的火山口都是负地形,火山口不存在高出地表的口沿。盖层岩石碎块覆盖在火山口的斜坡和底部,火山口的边缘的小断崖也是盖层岩石。地球物理检查结果表明,被土壤覆盖的下面和火山口的斜坡上的碎块也是盖层岩石。岩芯钻探揭示了至少存在五个岩石破碎带,这表明岩浆流体没有将这些破碎带的块体胶结而是水汽地下爆炸的结果。综合分析认为,岩浆在上升过程中遇到了丰富的含水层,产生了水汽,在遇到阻挡层后积聚能量,导致地下爆炸。地表岩石的崩塌始于中心,并导致周围岩石呈楔形崩塌。较大的玛珥式火山口的形成比小的经历了更多次的爆炸。本研究认为,这些玛珥式火山口形成于同一时代,具有相同的成因。全球对玛珥式火山口的研究表明,喷出的碎屑数量是由水参与岩浆活动的量决定的。然而,对于岩浆遇到丰富水层的情况下,由蒸汽冲撞地层和地下爆炸所形成的玛珥式火山口的研究很少。本文对辉腾锡勒玛珥式火山口的研究是对玛珥式火山口成因研究的贡献。

In the Huitengxile grassland of the Wulanchabu City,Inner Mongolia,there are hundreds of Maar craters with negative topography.They are numerous,densely distributed and well preserved.Their main features are all negative terrain and no crater rim above the surface rock.Basaltic layer and its fragments as the caprock cover the slope and bottom of the crater and there are small cliffs at the edge of the crater,which also have the composition of the caprock.Geophysical examination results also show that basaltic fragments hidden by soils cover the bottom and slope of the crater.Core drilling revealed at least five rock fracture zones,indicating that the possible magmatic fluid would have cemented these blocks.A comprehensive analysis shows that the magma encountered rich aquifer,produced water vapor,which accumulated energy after encountering barrier layer in the process of rising and led to underground explosions.The collapse of the surface rock began at the center of the crater and resulted in a wedgeshaped collapse around it.The larger Maar crater experienced more explosions than the smaller one.The authors also believe that these Maar craters have the same formation age and origin.Global studies on Maar craters show that the number of ejected debris is determined by amount of the water mixing with the magma.However,there is a lack of research on Maar craters formed by dash and break of steam only when magma encounters water rich layers.This study of the Maars in the Huitengxile basin is an important contribution to the formation of the Maar craters.