滇西昌宁-孟连带南段组碎屑锆石U-Pb年龄及其对沉积时代和构造环境的制约

U-Pb geochronology of the detrital zircons from the southern segment of the Changning-Menglian suture zone in western Yunnan:Constraints on sedimentary age and tectonic environment

为制约滇西昌宁-孟连带南段组的沉积时代和构造环境,阐明临沧地块演化特征,对南段组碎屑锆石进行U-Pb年代学研究。研究显示,南段组具统计意义的最年轻组碎屑锆石年龄为512 Ma、509.6 Ma,物源具泛非期(680~530 Ma)、晚格林威尔期(980~900 Ma)、早格林威尔期(1300~1100 Ma)3期年龄组段特点。结果表明,南段组中下部最大沉积下限为寒武纪,中上部上限为石炭纪。物源来自东冈瓦纳超大陆内部至少3条造山带,主要为南极Pinjarra造山带、西澳Albany-Fraser造山带、东澳Paterson-Peterman造山带,具亲冈瓦纳大陆性质。在古生代冈瓦纳大陆重建中,南段组古地理位置位于澳大利亚地块北缘,是一个从西澳大利亚地块往东澳大利亚地块,往北往东迁移,从被动大陆边缘到活动大陆边缘转换的演化过程。早期沉积环境为滨浅海或三角洲,后期为弧前增生楔沉积环境。

Clarify the evolution characteristics of the Lincang Block,it is necessary to restrict the sedimentary age and tectonic environment of the Nanduan Formaiton.The U-Pb geochronology of detrital zircon in the Nanduan Formaiton is studied in this paper.The study shows that the age of the youngest group from the Nanduan Formation are 512 Ma and 509.6 Ma.The source has the characteristics of three age groups:Pan African period(680~530 Ma),late Greenville period(980~900 Ma)and early Greenville period(1300~1100 Ma).The results show that it is considered that the maximum sedimentary lower limit of the Nanduan Formaiton is Cambrian,and the upper limit of the middle and the upper part is Carboniferous.The provenance comes from at least three orogenic belts in the East Gondwana supercontinent,which is mainly the Pinjarra orogenic belt in Antarctica,the Albany Fraser orogenic belt in Western Australia and the Paterson-Peterman orogenic belt in eastern Australia,with a pro-Gondwana continental nature.In the reconstruction of Gondwana continent in Paleozoic,the Nanduan Formation is located on the northern edge of the Australian plot,which expervenced an evolutionary process from the western Australia Block to the eastern Australia Block,moving north to East,and transforming from the passive continental margin to the active continental margin.The early sedimentary environment was coastal shallow sea or delta,and the later stage is forearc accretionary wedge sedimentary environment.