长白山天池火山CZK07钻所揭示的火山地层层序和火山作用特征

摘要

Tianchi volcano in Changbai Mountains is one of the largest active volcanoes on the earth.Its formation and evolution is very complicated.Based on the systematic compilation of drilling cores in and around Tianchi,this study carried out the CZK07 drilling program in this area.We analyzed the compositions of volcanic eruption material under Tianchi volcano cone at Baitoushan stage and the characteristics of volcanic stratigraphic sequences,and manifestation modes of the accompanying volcanism and active characteristics of fault structures during volcanic activities.CZK07 drilling core comprehensively records volcanic stratigraphic sequences of early activities,early and late shield-forming stages,and the pre-cone-forming stage after shield-forming.Among them,early activities in Tianchi volcano are reflected by strongly altered rhyrolite.The early shield formed in the Pliocene,and consists of Junjianshan Formation olive-basalt intercalated with pyroxene-basalt.The late-stage shield formed in the early Early-Pleistocene,and consists mainly of Manjiang Formation trachybasalt with intercalation with trachyte.It can be divided into three volcanic activities at least.The pre-cone-forming stage happened in the late Early-Pleistocene and volcanic eruption material consists of trachytic lava and its pyroclastic rock of the Xiaobaishan Formation.The accompanying volcanism includes basaltic subvolcanic rock during the late shield formation,trachytic subvolcanic activity accompanied with alteration and crypto-explosion during the cone-forming stage,and crypto-explosive breccias,hydrothermal alteration and alkaline-rhyolitic subvolcanic activity during the Holocene eruptions.High-angle extension-shear faults were very active since the Late-Cenozoic in the Tianchi volcano area,inferring that this was closely related to formation of "U" shaped Valley.%长白山天池火山是地球上最大的活火山之一,其形成演化过程复杂.本文在对天池周边工程钻岩芯资料系统整理的基础上,以本次在北坡“U”形谷中开展的CZK07钻岩芯为研究对象,揭示天池火山白头山期火山锥体之下的火山喷发物物质组成和火山地层层序变化特征,分析火山活动过程中伴生火山作用的表现形式及断裂构造的活动特征.CZK07钻岩芯较全面地记录了天池火山早期活动、早期造盾、晚期造盾和造盾之后前造锥阶段火山活动的火山地层层序.其中天池火山早期活动记录由蚀变较强的流纹岩组成;早期造盾由军舰山组橄榄玄武岩夹辉石玄武岩组成,形成于上新世;晚期造盾由漫江组粗面质(橄榄)玄武岩夹粗面岩组成,形成于早更新世早期,且至少存在3期火山活动;造盾之后前造锥阶段的火山喷发物由小白山组粗面质熔岩及碎屑岩组成,形成于早更新世晚期.伴生的火山作用记录表现为造盾晚期的玄武质次火山活动,造锥阶段的粗面质次火山活动及伴随发生的蚀变和隐爆现象,及全新世大爆发阶段的隐爆角砾、热液蚀变和次火山活动等现象.天池火山地区晚新生代以来高角度张剪性断层的活动强烈,推测与“U”形谷的形成密切相关.