羌塘地块作为近年地质研究的热点,其构造属性及是否存在太古面—元古宙基底等问题一直存在争议.文中采用LA-ICP-MS锆石U-Pb法对西藏荣玛牛山上三叠统日干配错组碎屑锆石进行年代学研究,结果表明:(1)日干配错组沉积岩中最年轻碎屑锆石年龄为(215±2)Ma,表明日干配错组的最大沉积年限为该时间,结合区域地质资料可将其沉积时代限定为晚三叠世诺利期—瑞替期.(2)年龄介于(580±6)～(212±2) Ma,峰值为(298±2)Ma,表明在晚古生代早期受古特提斯洋发育早期地壳减薄伸展阶段岩浆活动影响,冈瓦纳古陆为其物源区;峰值为(442±3)Ma,表明在中古生代受加里东期扬子板块和华夏板块碰撞、拼合而形成的岩浆活动的影响,物源区为扬子大陆周缘;只获得1颗锆石650～500Ma年龄,表明源区基本未受到泛非运动岩浆活动的影响.(3)碎屑锆石出现相对少量介于(1 091±6)～(757±6)Ma的年龄,表明在中—新元古代受格林威尔晋宁构造岩浆-热事件的影响,物源区与羌南地块一致.(4)日干配错组沉积岩碎屑锆石测年得到大量介于(3 214±7)～(1 380±15) Ma年龄值,占总量的近60％,峰值为(1 875±5)Ma和(2 531±6) Ma,表明羌塘地块受元古宙羌塘结晶基底主期构造-热事件和太古宙末全球超大陆拼合事件影响显著,且羌塘地块存在太古宙—元古宙基底.%The Qiangtang Block has become a geological research hotspot in recent years,however,its tectonic attributes,as well as the existence of Archean-Proterozoic basement in the block,have been controversial.In this work,using LA-ICP-MS zircon U-Pb technique,we performed detrital zircon dating for the sedimentary samples from the Rigain Pünco Formation in the Niu Mountain in Rongma,Tibet.The results show:(1) The youngest age of detrital zircon is 215 ± 2 Ma,equalling the maximum deposition age for the Rigain Pünco Formation.Combined with regional geological data,the deposition period was determined to be coincide with the Late Triassic Norian Rhaetian stage.(2) The zircon grain age ranges between 580± 6 and 212±2 Ma.The age peak at 298±2 Ma indicates the area was affected by the crustal thinning extensional stage magma activities during the Paleo-Tethys evolution in the Early Paleozoic.The age peak at 442±3 Ma shows that the area was affected by the magmatic activity due to the collision and accretion of the Caledonian Yangtze and Cathaysian plates in the Middle Paleozoic,and the provenance of the elastic rocks was the Yangtze continental margin.There is only one age occurrence at 650-500 Ma,suggesting the provenance region was almost unaffected by the pan-african magmatism.(3) Clastic zircon appears in relatively small amount and ages from 1091±6 to 757±6 Ma,showing that the area was affected by the tectonic magmatic thermal events of the Grenville-Jinningian in the southern Qiangtang Block.(4) A large number of detrital zircons are dated between 3214±7 and 1380± 15 Ma,they account for 60％ of total zircon samples from the Rigain Pünco Formation.The age peaks at 1875± 5 and 2531± 6 Ma show that,the Qiangtang block was affected by the Proterozoic crystalline basement main stage tectonic-thermal events,and the late Archean supercontinent split global events,hence providing a strong evidence for the existence of Archean-Proterozoic basement rocks in the Qiangtang Block.
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