河西走廊带与澳大利亚的亲缘性--来自牛首山中寒武统碎屑锆石U-Pb年龄和Hf同位素的证据

The affinity of the Hexi Corridor and Australia—Evidence from U-Pb geochronology and Hf isotopes of detrital zircons from Middle Cambrian strata in Niushoushan

在河西走廊带东端牛首山地区中寒武统的沉积岩中开展碎屑锆石原位LA-ICP-MS U-Pb定年和Hf同位素研究。结果表明,所采样品U-Pb年龄谱存在3个峰值：0.6~0.8Ga（峰值为669Ma）、1.0~1.3Ga（峰值为1173Ma）、1.6~1.8Ga（峰值为1710Ma）,明显区别于河西走廊带寒武系之上地层中的碎屑锆石U-Pb年龄谱。碎屑锆石U-Pb年龄谱和Hf同位素特征表明,典型的格林威尔期的物质和峰值为1710Ma的碎屑物质可能源于澳大利亚西南部,与现有的古生物学和古地磁学研究结果相吻合;中奥陶世随着北祁连洋的进一步扩张及其古地理位置的变化,碎屑物质的源区也随之变化,河西走廊带开始出现0.8~1.0Ga晋宁期的碎屑物质;晚奥陶世后由于祁连山的造山隆起、剥蚀、风化,河西走廊带记录了该地区0.4~0.5Ga的碎屑物质。

U-Pb geochronology and Lu-Hf isotopic studies of detrital zircons from middle Cambrian sediments of Niushoushan area, eastern Hexi Corridor, show three major groups of U-Pb age： 0.6-0.8Ga （peak at 669Ma）, 1.0-1.3Ga （peak at 1173Ma）, and 1.6- 1.8Ga （peak at 1710Ma）, which are significantly different from the detrital zircons U-Pb age spectrum of the upper strata in the Hexi Corridor belt. The characteristics of the detrital zircon U-Pb age spectra and Hf isotopes indicate that the detrital zircons 1.0-1.3Ga and 1.7-1.75Ga in age might have originated from southwest Australia, which is consistent with the evidence of paleontological and paleomagnetic studies in the Hexi Corridor. The Jinning-age （0.8-1.0Ga） detrital zircons that appear in the middle Ordovician strata in Hexi Corridor may indicate the changes of the source area of detrital materials, which resulted from the expansion of the North Qilian Ocean. The detrital zircons 0.4-0.5Ga in age extracted from post Ordovician strata were probably produced by the uplift of Qilian orogenic belt as well as the erosion and weathering processes in the Hexi Corridor.