火山斜坡堆积及其相模式——以松辽盆地营城组为例

Volcano slope deposition and its facies model:a case study of Yingcheng formation in Songliao basin

为了精细刻画盆地内火山斜坡堆积的岩相及其相结构,基于露头剖面和岩石样品观察分析的重要性,采用野外剖面地质研究和室内岩石样品成分、粒度组成分析相结合的方法,研究了松辽盆地东南缘露头区出露的营城组火山斜坡堆积相序与相结构.提出了包括热基浪、热碎屑流和空落3种亚相的火山斜坡爆发相单元结构.结果表明：爆发相由下到上为热基浪—热碎屑流—细空落亚相.其中热基浪亚相碎屑组成以刚性、炸裂状玻屑为主,粒度分析标准偏差0.93-1.26分选中等—好,偏度-1.85-3.46,显示牵引流粒度特征,发育层理构造;热碎屑流亚相碎屑组成主要是塑性—半塑性浮岩屑,少量炸裂状玻屑,粒度分析标准偏差0.87-1.65分选差,偏度-2.34-1.02,显示重力流粒度特征,顶部常发育浮岩屑层,浮岩屑变形程度与熔结程度呈近正相关,不发育层理构造;空落亚相,包括易识别的粗空落堆积和不易识别的细空落,刚性碎屑为主,分选好,常发育较好的水平层理,顶部常发育＂火山豆＂.

In order to describe lithofacies and its structure piled up by volcano slope deposition in the basin, this study surveyed the field profile geology, the composition of rock sample in the lab, and grain size composition, examined the facies sequence and facies structure of volcano slope of Yingcheng formation, and proposed the facies unit structure of explosive facies on volcano slope, including three subfacies, namely base surge deposition, pyroclastic flow and fine fallout deposition. The results show that the explosive facies are mainly base surge, pyroclastic flow and fine fallout subfacies from bottom up. The subfacies of base surge are mainly composed of rigid clast with angular shape, and standard deviation of grain size ranges from O. 93 to 1.26, but skewness are from --1.85 to 3.46, which indicates a middle-fine sorting and traction flow grain size characteristics, and bedding structures well developed. In the pyroelastic flow units, the volcanic elast are composed mainly of plastie-semiplastic pumice and less rigid clast, burst-like vitric, and standard deviation of grain size varies from 0. 87 to 1.65, but skewness changes between --2.34 and 1.02, which indicates a poor sorting and gravity flow grain size characteristics, and bedding structure poorly developed. Pumice layers are common on the top of pyroclastic flow subfacies, and the deform degree of pumice are positively correlated with welding degree of tuff. The fallout units are composed of coarse and fine pyroclast. The fine pyroclast are characterized by rigid clast, well sormess, horizontal bedding and ＂vol canic beans＂ structures on the top.