摘要
藏北南羌塘陆块北缘发育一套晚三叠世火山岩,命名为弄佰组。该组火山岩以玄武岩为主。岩石化学成分以低TiO_2、FeO+Fe_2O_3、K_2O为特征。∑REE介于162.91×10^(-6)383.4×10^(-6)之间,∑Ce／∑Y介于1.83～3.00之间,δEu介于0.47～0.97之间,平均为0.73,负Eu异常较明显。微量元素Sr、K、Rb、Ba、Th、Ce、Sm强烈富集,Ta、Nb、P、Ti、Cr相对亏损。岩石学和岩石地球化学特征表明弄佰组火山岩形成于消减带岛弧区。弄佰组火山岩出露于龙木错-双湖结合带的南侧,K-Ar同位素年龄值为223Ma±5Ma.与双湖带中蓝片岩和绿片岩相变质岩系的形成年龄(220～235Ma)基本一致,时空关系的紧密相连,说明其形成可能与晚三叠世龙木错-双湖古特提斯洋的南向俯冲消减事件有关。
A suite of Late Triassic volcanic rocks is developed at the northern margin of the south Qiangtang block, northern Tibet. It is named the Nongbai Formation. The volcanic rocks in this formation consist predominantly of basalt and are characterized by low TiO2, FeO＋Fe2O3 and K2O. ∑REE ranges between 162.91×10^-6 and 383.4×10^-6, ∑Ce/∑Y between 1.83 and 3.00, and 8Eu from 0.47 to 0.97 with an average of 0.73, exhibiting a negative Eu anomaly. The rocks are strongly enriched in the trace elements Sr, K, Rb, Ba, Th, Ce and Sm and depleted in Ta, Nb, P, Ti and Cr. The petrological and geochemical characteristics suggest that the volcanic rocks in the area formed in an island arc environment of a subduction zone. The volcanic rocks of the Nongbai Formation are exposed at the south side of the Lungmu Co- Shuanghu junction zone. Their K/Ar age is 223±5 Ma, which is in the main consistent with the age （220-235Ma） of the blueschist and greenschist metamorphic schist in the Shuanghu junction zone. The close temporal-spatial relation suggests that their formation was probably related to the southward subduction of the Late Triassic Lungmu Co-Shuanghu Paleo-Tethys Ocean.
出处
《地质通报》
CAS
CSCD
北大核心
2007年第6期682-691,共10页
Geological Bulletin of China
基金
中国地质调查局<西藏1:25万帕度错幅(145C004003)
昂达尔错幅(145C004004)区域地质调查>顶目(编号:200313000018)成果
关键词
晚三叠世
弄佰组
火山岩
构造环境
南羌塘陆块北缘
龙木错-双湖结合带
藏北
Nongbai Formation
Late Triassic
volcanic rocks
tectonic setting
northern margin of the south Qiangtang block
Lungmu Co-Shuanghu junction zone
northern Tibet
