CAJ | 학술논문

沉积物源分析是认识盆山演化的重要途径.四川盆地上三叠统的砾岩碎屑、砂岩骨架颗粒、碎屑重矿物组分显示,晚三叠世存在5大物源,它们分布于龙门山北段-中段、大巴山、龙门山南段、盆地东南和盆地南部.碎屑物源总体以"再旋回造山带"和"大陆板块"类型为主,其中,龙门山北段-中段和龙门山南段以"再旋回造山带"类型为主,而盆地东南部和南部以"大陆板块"类型为主."再旋回造山带"类型可细分为"混合造山带"及"碰撞造山和褶皱冲断带"两种类型,龙门山北段和龙门山南段均以"混合造山带"及"碰撞造山和褶皱冲断带"类型为特征.盆地物源分布存在阶段性特征:早期,龙门山北段-中段、大巴山物源规模较大,盆地东南和南部规模较小;晚期,盆地东南和南部规模增大,各方向呈均衡分布格局,这与周缘板块构造活动的阶段性有关.晚三叠世,龙门山北段由西北向东南方向挤压,构造活动强度总体具有弱-强-弱的演变趋势.须二期,龙门山北段逆冲-推覆开始形成,并暴露水面遭受剥蚀,向盆地提供物源;须四期为盆地最活跃期,龙门山北段进一步挤压抬升剥蚀,盆内沉积中心也由西北向东南迁移;须四期后,龙门山北段剥蚀区继续向东南推进,但构造活动强度渐趋和缓.
침적물원분석시인식분산연화적중요도경.사천분지상삼첩통적력암쇄설、사암골가과립、쇄설중광물조분현시,만삼첩세존재5대물원,타문분포우룡문산북단-중단、대파산、룡문산남단、분지동남화분지남부.쇄설물원총체이"재선회조산대"화"대륙판괴"류형위주,기중,룡문산북단-중단화룡문산남단이"재선회조산대"류형위주,이분지동남부화남부이"대륙판괴"류형위주."재선회조산대"류형가세분위"혼합조산대"급"팽당조산화습추충단대"량충류형,룡문산북단화룡문산남단균이"혼합조산대"급"팽당조산화습추충단대"류형위특정.분지물원분포존재계단성특정:조기,룡문산북단-중단、대파산물원규모교대,분지동남화남부규모교소;만기,분지동남화남부규모증대,각방향정균형분포격국,저여주연판괴구조활동적계단성유관.만삼첩세,룡문산북단유서북향동남방향제압,구조활동강도총체구유약-강-약적연변추세.수이기,룡문산북단역충-추복개시형성,병폭로수면조수박식,향분지제공물원;수사기위분지최활약기,룡문산북단진일보제압태승박식,분내침적중심야유서북향동남천이;수사기후,룡문산북단박식구계속향동남추진,단구조활동강도점추화완.
Analysis of depositional provenances is an important approach to understand the history of basin-range evolution. Mineral compositions of Upper Triassic conglomerate clasts and sandstone framework grains and heavy minerals in Sichuan Basin suggest five depositional provenances, which are distributed around the north-central Longmenshan, south Dabashan, south Longmenshan, southeastern and southern Basin. The clastic depositional provenances are dominated by the recycled orogen zone and continental plate type, with the former in the middle, north, and south Longmenshan, and the latter in the south-east and the south Sichuan Basin. The recycled orogen can be subdivided into two types: mixed orogenic belt, and collision orogen and fold thrusting fault belt, with both occurring in north and south Longmenshan. The distribution of depositional provenances displays different stages. In the early stage, depositional provenances were distributed dominantly in the middle-south part of Longmenshan and Dabashan, with limited deposits from the south-east and south Sichuan Basin. In the late stage, the south-east and south Sichuan Basin provided much sediment increasingly, leading to balanced distribution of depositional provenances, and this may be related to periodic tectonic activities of circumferential plate. During Late Triassic, the north Longmenshan experienced an NW-SE compression and intensity of tectonic activities also experienced a change trend from weak and then strong to weak.During the member 2 sedimentary period of Upper Triassic, Longmenshan area began thrusting and overlapping, and then denuded after exposing groundwater, which provided substantive sediments to Sichuan Basin. The member 4 sedimentary period of Upper Triassic was characterized by intensive tectonic activity, which resulted in further compression-lifting-denudation of north Longmenshan. The depocenter of the basin migrated from northwest to southeast basin. Afterwards,the denudation of north Longmenshan advanced from NW to SE basin continually, but tectonic intensity was weakening gradually.