青藏高原羌塘中部果干加年山上三叠统望湖岭组的建立及意义  

Establishment of the Upper Triassic Wanghuling Formation at Guoganjianian Mountain, central Qiangtang, Qinghai-Tibet Plateau, and its significance

作　　者：李才[1] 翟庆国[1] 董永胜[1] 于介江[1] 黄小鹏[1] 

机构地区：[1]吉林大学地球科学学院,吉林长春130061

出　　处：《地质通报》2007年第8期1003-1008,共6页Geological Bulletin of China

基　　金：国家自然科学基金项目(编号:40672147);中国地质调查局项目(编号:1212010561605;200313000015)资助。

摘　　要：在果干加年山的主脊及其以北识别出一套稳定的沉积岩系,角度不整合于蛇绿混杂岩之上,以细砂岩、硅质粉砂岩为主,其中夹有大小不等的古生代外来岩块,底砾岩成分因地而异并具有快速堆积的特点,底部夹有流纹岩。厚度大于1633m。流纹岩夹层获得的锆石SHRIMPU-Pb谐和年龄为214Ma±4Ma,时代为晚三叠世诺利期。在剖面测制和区域对比的基础上建立了上三叠统望湖岭组,代表龙木错-双湖缝合带闭合以后接受的最早的沉积盖层。望湖岭组之下的蛇绿混杂岩获得阳起石Ar-Ar年龄219.7Ma±6.5Ma。同位素定年确定构造转化事件发生在214～220Ma之间,为龙木错-双湖缝合带的闭合时间提供了确切的时间约束,望湖岭组是这一事件的沉积记录,是龙木错-双湖缝合带蛇绿混杂岩之上首次发现的沉积盖层。A uniform sedimentary series is recognized at the main ridge of Guoganjianian Mountain, central Qiangtang, Qinghai-Tibet Plateau. Unconformably overlying ophiolitic mélange, it consists predominandy of fine sandstone and siliceous siltstones, intercalated with some Paleozoic exotic blocks of varying sizes. The composition of basal conglomerate varies from place to place and shows the features of rapid accumulation, with rhyolite intercalated at the bottom. The sedimentary series has a thickness of 1633 m, The rhyolite interlayer has a SHRIMP U-Pb zircon concordia age of 214±4 Ma, indicating a Late Triassic Norian age. The Upper Triassic Wanghuling Formation is established based on the section measurements and regional correlation. It represents the oldest sedimentary cover formed after the dosing of the Lungmu Co-Shuanghu suture. The ophiolitic mélange below Wanghuling Formation has an actinolite Ar-Ar age of 219.7±6.5 Ma, which suggests the tectonic transformation event took place between 214 and 220 Ma. This provides an exact time constraint on the closing age of the Lungmu Co-Shuanghu suture and the Late Triassic Wanghuling Formation is the sedimentary record of this tectonic event and the first sedimentary cover above the ophiolitic mélange in the Lungmu Co-Shuanghu suture.

关 键 词：青藏高原 羌塘中部 果干加年山 晚三叠世 望湖岭组 不整合 沉积制约 

分 类 号：P534.51[天文地球—古生物学与地层学]