古地理环境对火山喷发样式的影响:以准噶尔盆地玛湖凹陷东部下二叠统风城组为例*
Effects of palaeogeographic environment on volcano eruption style: Example from the Lower Permian Fengcheng Formation in eastern Mahu sag,Junggar Basin

自然界中,火山的喷发样式常因岩浆或周围环境的变化而发生转换。为了探索沉积盆地古地理环境对古代火山喷发样式的可能影响,文中利用地震、钻测井及岩心资料,厘定准噶尔盆地玛湖凹陷东部下二叠统风城组古地理环境及火山岩的分布;利用岩心和薄片观察、扫描电镜、元素地球化学、电子探针等技术,对取心段火山岩岩石类型、岩石组合和地球化学特征开展了研究。结果表明:(1)取心段火山岩发育4种岩石类型和3种岩石组合,射气岩浆喷发和岩浆喷发2种火山喷发样式类型;(2)射气岩浆喷发以发育熔积岩,具面包皮结构、熔结结构、熔结珍珠结构的熔结凝灰岩和增生火山砾为特征,而岩浆喷发以胶结增生火山砾而形成含增生火山砾熔岩为特征;(3)火山口古地理环境的演化控制着火山喷发样式的类型及其转换,进而影响喷发产物的特征:古地理环境为水下环境时,足量的水和上升的高温岩浆相互作用发生射气岩浆喷发;古地理环境变为陆上时,岩浆发生溢流式岩浆喷发。取心段古地理环境变化的主要原因可能是喷发产物在火山口附近的堆积或季节性气候变化引起的湖平面变化;(4)古地理环境对古代火山喷发的样式类型、喷发过程、喷发产物特征具有重要影响,这可以为盆地中火山岩成因分析和喷发过程重建提供新的视角,为火山岩油气藏的精细勘探开发提供新的思路。
The eruption style transition of modern volcanoes often occurred,due to the changes of magma or ambient environment in nature. This paper tries to explore the probable influences of palaeogeographic environment on volcano eruption style in the sedimentary basin. Based on data from seismic,drilling,logging and core,the palaeogeographic environment and distribution of volcanic rocks in the Lower Permian Fengcheng Formation in eastern Mahu sag,Junggar Basin,were analyzed. The petrological and geochemical characteristics of cored volcanic rocks were studied by core observation,thin section observation,SEM(scanning electron microscope),major element analysis and EPMA(electron probe microanalysis). The results showed that:(1)There are mainly four types of volcanic rock and three types of lithological association. Two kinds of eruption style,phreatomagmatic eruption and magmatic eruption,are recognized. (2)In detail,phreatomagmatic eruption is characterized by peperite,accretionary lapilli and welded tuff developed with bread-crusted texture,welded texture and welded perlitic texture. While,magmatic eruption is characterized by accretionary lapilli-bearing lava caused by the cementation of earlier accretionary lapilli. (3)The evolution of palaeogeographic environment near vent controlled the eruption style,which then influenced the characteristics of eruptive products. Phreatomagmatic eruption caused by magma and enough water interaction occurred when palaeogeographic environment was subaqueous. Effusive magmatic eruption happened when palaeogeographic environment was subaerial. The major reason of palaeogeographic environment changes probably were related to the accumulation of eruptive products near vent or lake level changes caused by seasonal weather change in the core intervals. (4)Therefore palaeogeographic environment had significant influences on eruption style,eruptive