准南地区下二叠统火山岩-沉积岩互层叠置发育模式

Developmental patterns of interbedded volcanic and sedimentary rocks in the Lower Permian of Zhunnan area

通过野外露头观测与样品采集,对准南地区下二叠统火山岩-沉积岩互层叠置发育特征和发育模式开展火山岩相学、样品测试和室内综合分析等研究。结果表明:研究区火山岩以基性火山岩(玄武岩)和酸性火山岩(英安斑岩或流纹岩)伴生出现为主要特征,具有双峰式火山岩的岩石组合特征。沉积岩以砾岩、砂砾岩为主,砾石成分主要为火山岩和火山碎屑岩,成分成熟度和结构成熟度均较低。火山岩-沉积岩互层叠置地层序列以玄武岩、英安斑岩与火山角砾岩或砂泥岩互层产出为特征,划分为火山爆发相、次火山岩相、火山喷溢相、冲积扇扇根亚相、冲积扇扇中亚相和冲积扇扇缘亚相6种岩相类型以及中性旋回、中-酸性旋回、沉积旋回和基性火山-沉积旋回4个旋回。在大陆裂谷的背景下,软流圈地幔上涌形成的玄武质岩浆与其底侵下地壳物质发生熔融形成的酸性岩浆混合,形成流纹岩或流纹斑岩、玄武岩,与火山活动间歇期形成的沉积岩互层叠置。

Based on outcrop observation and sample collection in the field,the study of developmental patterns and charac？teristics of interbedded volcanic and sedimentary rocks in the Lower Permian of Zhunnan area was carried out through vol？canic petrographic analysis,sample test and indoor comprehensive analysis. The result shows that the volcanic rocks in this area are mainly composed of basic volcanic rocks（basalt）and its associated acidic volcano rocks（dacite porphyry or rhyo？lite）,which would be present as bimodal volcanic rock combination haracteristics. Conglomerates and glutenite are mainlydeveloped in the sedimentary rocks. The main components of the gravel are volcanic rocks and pyroclastic rocks,and their composition maturity and structural maturity are relatively low. The sequence of interbedded volcanic and sedimentary rockstrata is characterized by alternation of basalt,dacite porphyry and volcanic breccia or sand and mudstone. Six types of lithofacies can be divided as volcanic eruption facies,subvolcanic facies,volcanic effusive facies,alluvial fan fan-root sub？facies,alluvial fan fan-middle subfacies and alluvial fan margin subfacies. Four cycles can be divided as neutral cycle,neu？tral-acid cycle,sedimentary cycle and basic volcanic sedimentary cycle. Under the structural background of continentalrift,the basaltic magma formed by the upwelling asthenosphere mantle is melted with the undercut crustal material to be？come mixed acidic magma,and thus the rhyolite,rhyolite porphyry and basalt were formed,interbedded with the sedimenta？ry rocks formed during the intermittence period after the volcanic activity.