中基性火山作用喷出物类型、特征与成因

Classification,Description and Interpretation of the Volcanic Products:Ancient and Modern Examples from China

基于松辽盆地中生代和准噶尔盆地古生代火山岩研究资料与长白山、五大连池等现代火山考察,结合国外典型实例,将火山作用喷出物分为熔岩、碎屑熔岩、火山碎屑岩和沉火山碎屑岩4类;前两类岩石冷凝固结,后两类压实固结。按成分-组构-岩相分类方案划分出34种岩相。详细论述了各岩相的成岩方式、成分、组构、成因和产状,并给出各岩相类型的实例和典型照片。建造-改造和继承-变异分析对比显示,现代火山与古火山都常见的岩相包括厚层熔岩、熔结结构碎屑熔岩、柱状节理熔岩、枕状熔岩和玻璃质熔岩。现代火山常见而古火山少见或未见的有浮岩、渣状熔岩、绳状和块状熔岩。火山穹窿垮塌是常见的同生改造作用。裂隙式与中心式喷发往往相伴而生,常表现为沿着深大断裂的一系列中心式喷发。

The volcanic products in China were classified into 4 groups including lava,pyroclast-bearing lava,tephra and tuffites,according to the research on the ancient volcanic rocks of the Songliao basin in Cretaceous and the Junggar basin in Carboniferous and also on the Quaternary volcanoes like Changbai and Wudalianchi.The former two groups are consolidated by cooling/crystallization and the latter two by compaction.Thirty four essential lithofacies/intrafacies were further subdivided and described in detail concerning their structure/texture,composition/component,distribution and origin.Typical examples ancient and modern are presented in photographs related to each intrafacies.There are both sameness and difference between modern and ancient volcanic products.Diversity of lavas such as coherent massive,columnar joint,welded,pillow and breccia can survive in the long geological history,becoming relatively more abundant in the ancient volcanoes.On the other hand,pumice,aa and block lavas become less and less with time owing to their poor preservation because they are generally on top or edge of a volcanic succession and/or with features of being easily eroded and transported.For most ancient volcanoes like those in the Mesozoic Songliao basin,it is very common that eruptions are mixed pattern between the fissure and the central,i.e.most single central vents are associated with or ranged along some major faults.