CAJ | 학술논문

首次在藏北羌塘中部达瓦山地区识别出一套复理石沉积,厚度大于3000m,未见顶底,岩石组合以变质砂岩、杂砂岩和千枚岩为主,夹双峰式火山岩,火山岩岩性为流纹岩和玄武岩.用LA-ICP-MS同位素测定技术对流纹岩夹层中的锆石进行了U-Pb同位素测定,获得锆石的年龄为454.0±2.0Ma和458.3±1.8Ma,时代为中晚奥陶世达瑞威尔—桑比期,代表了达瓦山组的主体形成时代.在剖面测制和区域对比的基础上建立了中—上奥陶统达瓦山组,代表冈瓦纳大陆北缘中—晚奥陶世裂谷型深水-半深水复理石沉积.中—上奥陶统达瓦山组的发现和建立完善了该区中晚奥陶世的地层系统,进一步确定该区中—晚奥陶世洋盆的存在,对冈瓦纳大陆北缘中—晚奥陶世岩相古地理研究具有重要意义.
수차재장북강당중부체와산지구식별출일투복리석침적,후도대우3000m,미견정저,암석조합이변질사암、잡사암화천매암위주,협쌍봉식화산암,화산암암성위류문암화현무암.용LA-ICP-MS동위소측정기술대류문암협층중적고석진행료U-Pb동위소측정,획득고석적년령위454.0±2.0Ma화458.3±1.8Ma,시대위중만오도세체서위이—상비기,대표료체와산조적주체형성시대.재부면측제화구역대비적기출상건립료중—상오도통체와산조,대표강와납대륙북연중—만오도세렬곡형심수-반심수복리석침적.중—상오도통체와산조적발현화건립완선료해구중만오도세적지층계통,진일보학정해구중—만오도세양분적존재,대강와납대륙북연중—만오도세암상고지리연구구유중요의의.
In this paper, a set of flysch sediments were firstly discovered in central Qiangtang, northern Tibet. Their thickness is more than 3000 m, and the top and bottom were not observed. Rock association consists of metamorphic sandstone, greywacke and phyl-lite, intercalated with bimodel volcanic rocks. The main lithology of the volcanic rocks includes rhyolite and basalt. The results of zir-con LA-ICP-MS U-Pb dating indicate that the rhyolite rocks formed at 454Ma and 458Ma, indicating Middle-Late Ordovician Darriwilian-Sandbian age, which represents the formation age of Dawanshan Formation. The Middle-Upper Ordovician Dawashan Formation was established based on the section measurement and regional correlation, which shows that the abyssal-bathyal flysch was formed in the rift of northern Gondwana continent margin in the Middle-Late Ordovician. The establishment of Dawashan For-mation contributes to the improvement of Ordovician stratigraphic system and also confirms the existence of Middle-Late Ordovi-cian Ocean in this area. The results obtained by the authors are of great importance for the study of the Middle-Late Ordovician lithofacies paleogeograghy on the northern margin of Gondwana continent.