克百断裂带上盘石炭系火山喷发期次划分与火山岩分布规律OA

The volcanic rocks in the upper plate of the Kebai Fault Zone in the Carboniferous system ex-hibit complex and variable lithology and lithofacies,with multiple stages of volcanic rock superimposi-tion,resulting in chaotic seismic reflection characteristics and unclear hydrocarbon distribution patterns.Based on integrated geochemical,lithological,well-log,and seismic data,the tectonic setting,geolog-ical age,and petrological characteristics of the study area were clarified,leading to the establishment of criteria for dividing volcanic eruption cycles and stages,as well as defining the distribution patterns of volcanic rocks.Results indicate that the Kebai Fault Zone developed in an island-arc tectonic setting,with an age of approximately(316.8±2.9)Ma,and exhibits a lithofacies sequence transitional from vol-canic lava to pyroclastic rocks.One eruption cycle was identified in the study area,bounded primarily by unconformities and weathering crusts.The Carboniferous system in the Kebai Fault Zone can be divided into five stages(C1-C5):the C1 stage is dominated by andesite,with a sedimentary interlayer of tuf-faceous sandy conglomerate at the top;the C2 stage consists of interbedded andesite and tuffaceous sandy conglomerate,topped by a tuffaceous sandy conglomerate marking the stage boundary;the C3 and C4 stages are characterized by tuffaceous sandy conglomerate and tuff as key lithological and lithofa-cies indicators;the C5 stage develops tuffaceous sandy conglomerate,forming a weathering crust in un-conformable contact with the Jurassic strata.The Chemical Index of Alteration(CIA)values for stages C1-C5 show alternating intensity of alteration,reflecting periodic changes in weathering conditions.Laterally,volcanic lava extends from north to south with progressively reduced distribution and dimin-ished eruption intensity.These results provide guidance for characterizing the vertical sequence and spa-tial distribution of different volcanic stages in the study area.