ABSTRACT

The Precambrian–Palaeozoic evolution of the Qilian orogen is widely debated due to the complexity of the orogen’s structure and the extent of Phanerozoic deformation. In order to identify the tectono-magmatic events of the Qilian orogenic belt, we conducted detrital zircon U-Pb geochronology on river sediments across the orogen. The results indicate that the detrital zircon ages mainly comprise five populations: 220–280 Ma, 400–520 Ma, 800–1000 Ma, 1200–2100 Ma, and 2200–2700 Ma. The sediments in the Central Qilian Block exhibit zircon age peaks at ~1.8 Ga and ~1.0 Ga, which support that the Central Qilian Block successively accreted to the Columbia and Rodinia supercontinents. The sediments in the Quanji Block exhibit zircon age peaks at ~1.8 Ga and ~2.5 Ga, revealing possible affinity of the Quanji Block to the North China Craton prior to the Neoproterozoic. The detrital zircon age population in 400–520 Ma of all the sediments recorded the continental aggregation process among the Quanji, Qaidam, and Central Qilian Blocks. The widespread 200–300 Ma zircon ages in Central Qilian, Quanji, and North Qaidam regions, reflect a tectono-magmatic event which was most likely associated with the low-angle Paleo-Tethys subduction at the southern margin of Qaidam Block. Our results underline that the overlooked Neoarchean to Paleoproterozoic and Permian to Triassic tectono-magmatic events of the Qilian orogenic belt deserves more attention in the future study. The detrital zircon age populations of different river sand samples indicate fairly high variability, highlighting that caution should be exercised while using modern river sand detrital zircon age signatures to track tectono-magmatic history of such complex orogens.

摘要

由于造山带结构的复杂性和生代变形的程度，对祁连造山带的前寒武纪-古生代演化进行了广泛的争论。为了确定祁连造山带的构造-岩浆事件，我们对造山带上的河流沉积物进行了碎屑锆石U-Pb年代学研究。结果表明，碎屑锆石年龄主要包括五个种群：220-280 Ma，400-520 Ma，800-1000 Ma，1200-2100 Ma和2200-2700 Ma。祁连中部地区的沉积物在〜1.8 Ga和〜1.0 Ga处表现出锆石年龄的峰值，这支持了祁连中部地区先后向哥伦比亚和罗迪尼亚超大陆增生。全济区块的沉积物在〜1.8 Ga和〜2.5 Ga处表现出锆石年龄峰值，揭示了新元古代之前全济地块对华北克拉通的可能亲和力。在所有沉积物中400-520 Ma的碎屑锆石年龄种群记录了全济，柴达木和祁连中部地块的大陆性聚集过程。祁连中部，全济和柴达木北部地区普遍存在200-300 Ma锆石年龄，反映了构造岩浆事件，最有可能与柴达木地块南缘的低角度古特提斯俯冲有关。我们的研究结果表明，祁连造山带的新古纪至古元古代和二叠纪至三叠纪构造岩浆事件被忽视，值得在未来的研究中给予更多的关注。不同河砂样品的碎屑锆石年龄种群显示出相当高的变异性，