松潘地区尕海盆地上白垩统热鲁组物源分析及其意义

运用Dickinson三角图解和碎屑锆石年龄分析方法,对松潘地区白龙江隆起西段尕海盆地上白垩统热鲁组物源及沉积背景进行了研究。热鲁组砂岩岩屑以变质岩为主,碎屑物质成分和结构成熟度较低;Dickinson三角图解显示热鲁组砂岩物源主要来自再旋回造山带的石英再旋回和过渡再旋回带;碎屑锆石分析显示最新年龄为137Ma,指示该地层时代应晚于早白垩世早期;碎屑锆石U-Pb年龄基本上继承了区域上三叠纪地层的碎屑锆石年龄分布特征,说明热鲁组碎屑物质主要来自于区域上三叠纪地层,较少或几乎没有来自前三叠纪地层,而现今展布于盆地周围的下伏前三叠纪地层,晚白垩世时期尚未出露遭受剥蚀,同时这一结论也与松潘地区的热年代学数据揭示的构造背景相一致。

Provenance Study on Sediments in the Gahai Basin of the Songpan and its Geological Significance

The Songpan-Ganzi fold belt in central China is located in the junction of the Qiangtang Block, North China Block and Yangtze Block. In this region, the the pro-Triassic sequences are well developed, while the sediments of Jurassic and Cretaceous are rare. The research of the Gahai basin provides significant information about the evolution of the Jurassic and Cretaceous sedimentation. Using detrital zircon geochronology and Dickinson triangular plots, distinct sediment sources of the Relu Formation can be distinguished in the Gahai basin which is in the Bailongjiang uplift of Songpan-Ganze block. The types of detritus and quartz indicate that the provenance is mainly metamorphic rocks, with low compositional and textural maturities. The source originates from the quartzose recycled origin and transitional recycled origin as exhibited in the Dickinson triangular plots. The youngest concordant age of the detrital zircons from the Relu Formations is 137 Ma, which indicates that the Relu Formation was developed in Late Cretaceous. The results show that the detrital zircons in the Relu Formation were inheritance from the Triassic strata in Songpan-Ganze area. It suggests that the provenance of the Relu Formation was mainly derived from recycled Triassic sedimentary of the Songpan-Ganze complex near Bailongjiang uplift. Actually, the underlying pre-Triassic strata occurring around the basin were not uplifted as denudation areas and provided sediment material to the Gahai basin in Late Cretaceous,which is also supported by the thermochronological results.