鄂西秭归盆地中三叠世-早侏罗世沉积记录及其对秦岭印支碰撞造山作用的启示  

Middle Triassic-Early Jurassic Sedimentary Record in the Zigui Basin and Implication for the Qinling Indosinian Collisional Orogensis

作　　者：柴嵘 杨江海[1,2] 杜远生[1,2] 丁典识 

机构地区：[1]中国地质大学(武汉)生物地质与环境地质国家重点实验室,武汉430074 [2]中国地质大学(武汉)地球科学学院,武汉430074

出　　处：《地质科技情报》2016年第4期43-49,共7页Geological Science and Technology Information

基　　金：国家自然科学基金项目(41272120;41302083)

摘　　要：随着印支期南秦岭勉略洋盆闭合，华南和华北两大块体最终拼贴、构成中国大陆的基本轮廓。普遍认为这一洋陆转换、碰撞造山发生在三叠纪，但具体时间和空间过程仍存在较多争议。秭归盆地位于秦岭逆冲褶皱带东段南缘，是扬子北缘前陆盆地系统的重要组成，在沉积序列和碎屑来源上与秦岭印支期造山作用密切相关。该盆地经历早中三叠世滨-浅海相到晚三叠世-早侏罗世三角洲-河流相的沉积转变，中三叠统巴东组和上三叠统九里岗组之间发育平行不整合。不整合面之上的上三叠统一下侏罗统砂岩在碎屑组分上不仅含有泥岩、粉砂岩等沉积岩岩屑和千枚岩、板岩和片岩等中-低级变质岩岩屑，而且还见有中酸性火山岩岩屑。结合碎屑锆石颗粒U—Pb定年和古流向数据，这些火山岩岩屑揭示北部的秦岭造山带源区在晚三叠世（225～200Ma）存在火山活动，与同期的花岗质侵入岩一起反映秦岭印支期的同碰撞造山岩浆活动。The closure of the Mianlue Ocean in the south Qinling region occurred during the Triassic In- dosinian orogeny, causing the North China and South China to coalesce and thus forming the proto Chinese continent. This Triassic assembly has been widely accepted, but its exact time and spatial processes re- mained to be confirmed. The Mesozoic Zigui Basin,located to the south of eastern Qinling Orogen, consti- tutes part of the northern Yangtze foreland basin system, where the deposition and sedimentary prove- nance are closely related to the orogenic processes o{ the Qinling Orogen. This basin evolves from the Ear- ly-Middle marine to the Late Triassic-Early Jurassic, forming dehaic-riverine sedimentary facies with a weathering crust separating the Badong and Jiuligang formations, with a disconformity between the under- lying and overlying strata. Sandstones ofthe Jiuligang and Tongzhuyuan formations contain sedimentary, metamorphic and volcanic rock fragments, which directly denote a provenance where corresponding rocks were exposed and eroded. The felsie and microlitic textures of the volcanic rock fragments suggest first-cy- cled detritus from andesitic-rhyolitic source rocks. In combination of the domination of 230--200 Ma popu- lation in the detrital zircons of the Late Permian-Early Triassic samples, the presence of andesite-rhyolite detritus and southward paleocurrents would signify Late Triassic volcanism in the north and the eastern Qinling Orogen. Such volcanism probably represents an extrusive counterpart of the widely reported gran- itoid plutons in the Qinling Orogen and seemly responds to the Indosinian collisional orogensis there.

关 键 词：秭归盆地 洋陆转换 碰撞造山 沉积序列 碎屑沉积物源 

分 类 号：P534.5[天文地球—古生物学与地层学]