福贡地区石炭系地层可能属于拉萨地块:来自碎屑锆石年龄谱的指示

欧亚与印度大陆的碰撞使得印度大陆的北东角强烈挤入欧亚大陆内部,形成东构造结,其引发的强烈变形将南羌塘地块、北羌塘地块、拉萨地块、保山地块、兰坪-思茅地块以及地块之间的缝合带挤压于很窄的范围内,造成青藏高原腹地与其东南缘之间构造单元划分、对比困难。滇西福贡地区位于青藏高原东南缘,东构造结影响范围内,是三江造山带及青藏高原相关地块的汇聚处。福贡地区石炭系岩石组合表明其形成于较为稳定的浅海相沉积环境中,具有被动大陆边缘沉积特征。三件石炭系二云母石英片岩碎屑锆石表面年龄数据(194个有效分析点)形成五个主要年龄区间:2550~2400Ma、1800~1550Ma、1200~1080Ma、1000~850Ma和600~480Ma,峰值分别为~2502Ma、~1724Ma、~1120Ma、~886Ma和~512Ma。对比其他地块同时代地层的碎屑锆石年龄谱表明,福贡地区石炭系可能是拉萨地块的一部分,与腾冲地块一样,属于其南延部分。结合中新生代岩浆岩带的构造连续性,我们认为,印度板块东北角向北、北东方向的强烈挤压导致拉萨地块及冈底斯岩浆岩带弯曲、缩颈、并发生分离与旋转。

The Carboniferous strata in the Fugong region, western Yunnan likely belong to the Lhasa terrene: Evidence from detrital zircon U-Pb age-spectra.

Impingement of the India continent into the Eurasia along the Eastern Himalaya Syntax greatly modified the tectonic pattern of the southeastern Tibetan Plateau, where several continental blocks, such as southern and northern Qiangtang, Lhasa, Baoshan, and Tengchong blocks, and the sutures between them have been merged in a narrow region. As a result, it is hard to reveal the relationships between these tectonic units. The Fugong region is located in the east of the Eastern Himalaya Syntax, and is consisted of several blocks of the Tibetan Plateau and of the Sanjiang Orogenic Belt. This paper reports LA-ICP-MS U-Pb dating results of detrital zircons from the Carboniferous strata in the Fugong region. Field and petrological study demonstrated that these strata are of shallow marine facies likely in a passive continental margin. Detrital zircon U/Pb analyses of three quartzite samples reveal five major ²⁰⁶Pb/²³⁸U age-intervals:2550~2400Ma, 1800~1550Ma, 1200~1080Ma, 1000~850Ma and 600~480Ma, which are peaked at~2502Ma,~1724Ma,~1120Ma,~886Ma and~512Ma, respectively. This age spectrum suggests that the Upper Paleozoic strata in Fugong area are highly comparable with those of the Lhasa block. Taking the spatial continuity of the Cenozoic magmatic belt in southeastern Tibet into account, these strata, along with those of the Tengchong block, seem to be the southern extending of the Lhasa block, which likely had resulted from stretching, bending and rotation of this block due to the impingement of the India continent along the Eastern Himalaya Syntax.