楚雄前陆盆地的充填层序与造山作用

INFILLING SEQUENCES AND OROGENESIS IN THE CHUXIONG FORELAND BASIN,YUNNAN

关键词:  前陆盆地  充填层序  造山作用  楚雄

Key words:  foreland basin  infilling sequence  orogenesis  Chuxiong

摘要:

楚雄盆地是一中生代前陆盆地,发展过程有两个阶段:晚三叠世卡尼期至诺利期为前陆复理石充填期;诺利晚期至瑞替期为前陆磨拉石充填期。相应的形成两个二级层序和四个三级层序。层序的构型显然与造山过程耦合。哀牢山前缘逆冲带推进的速度控制着楚雄盆地基底挠曲幅度,因而决定了盆地的沉降率;逆冲带隆升幅度则决定了陆源区的物源供给量。由于可容空间和物源供给率是控制盆地层序地层格架的两个基本因素,因此前陆逆冲载荷的迁移就是控制层序地层的关键。作者以盆地中的充填层序反馈哀牢山造山作用的特点和过程:早、中期,盆地中以向上变深的二级沉积层序代表了哀牢山逆冲的初始价段,逆冲载荷达到盆地拉张变薄的基底上,前陆挠曲幅度大,造山带抬升的相对高度较低。晚期,盆地中以向上变浅的二级沉积层序代表了逆冲载荷推进到克拉通基底上,地壳挠曲受阻,物源供给量加大。三级沉积层序的相互叠置则反映了造山带多幕次、多周期活动的特点。

Abstract:

The Chuxiong Foreland Basin,a Mesozoic foreland basin installed on the southwestern margin of the Yangtze plate has seen two stages of development;the foreland flysch infilling stage from the Carnian to Norian (Late Triassic),and the foreland molasse infilling stage from the late Norian to Rhaetian (Late Triassic),during which two second-order sequences and four third-order sequences were correspondingly generated.The progradation velocities of the Ailaoshan frontal thrust zone got control of the upwarping amplitudes of the basement and the subsidence rates of the Chuxiong Foreland Basin,and the uplifting amplitudes of the thrust zone commanded the supply rates of the terrigenous clasts.Seeing that the accommodation spaces and supply rates are considered to be two fundamental factors for controlling sequence stratigraphic framework of the basin,the migration of the foreland thrust load is interpreted as the key factor for controlling the sequence stratigraphy of the basin.The research results in the present paper have disclosed the characteristics and processes of orogenesis with the aid of the infilling sequences in the basin.The early and middle deepening-upward second-order sedimentary sequences in the basin indicate that the thrust load was prograded onto the cratonic basement.The upwarping rates of the crust decreased,and the supply rates of sediments increased.The mutual superimposition of the third-order sedimentary sequences has revealed the multiphase and multistage orogenesis in the orogenic zone.