罗布泊第四纪湖盆物源与盆地构造演化特征：来自LDK01孔碎屑锆石U-Pb年龄证据

为揭示罗布泊盐湖第四系潜在物源区及凹陷阶段性演化过程,本文对罗布泊第一口钾盐科探深钻LDK01孔更新统不同深度样品进行碎屑锆石U-Pb微区定年分析。Th/U比值显示,钻孔碎屑锆石类型主要为岩浆锆石,少量为变质成因锆石。锆石年龄主要集中在209~240Ma、265~304Ma、320~385Ma、406~446Ma、705~880Ma及2376~2405Ma几个区间。综合分析潜在物源区的岩石属性和年龄构成,初步认为罗布泊地区前寒武纪年龄来自北部山前库鲁克塔格地区,加里东期碎屑锆石可能来源于阿尔金造山带和(或)南天山构造带。276Ma的峰值记录了塔里木盆地二叠纪大火成岩省事件,南天山最有可能为主导物源区。印支期和新生代碎屑锆石年龄暗示了北山地块和东天山,甚至较远的帕米尔-西昆仑山等地可能也提供了物源。凹陷周缘富钾岩体广泛出露,经风化、淋滤搬运至罗布泊,为凹陷第四纪成钾提供了有利的物质来源。塔里木盆地内部流域带来的碎屑组分是主要的物质来源,近源地区造山带岩体提供的物源有限。碎屑锆石年龄纵向变化特征显示,罗布泊北部地区在中更新世发生一次明显的构造抬升,可能是导致罗北凹地形成的重要原因。

Provenance of the Quaternary Lake Basin and Tectonic Evolution of the Basin in Lop Nur: Evidence from Detrital Zircon U-Pb Age of Core LDK01

Detrital zircon U-Pb age analyses for the samples from the first scientific potash exploration drill core in Lop Nur were conducted to reveal the potential source area of the Quaternary salt lake and stage tectonic evolution of the depression in Lop Nur. Th/U ratios show that the detrital zircons are dominantly magmatic origin, with minor metamorphic zircons. Zircon ages are concentrated mainly in the ranges of 209~240Ma, 265~304Ma, 320~385Ma, 406~446Ma, 705~880Ma and 2376~2405Ma. Combined with the rock nature and age range of the potential source area, it can be preliminarily concluded that the pre-Cambrian materials mainly sourced from the Kuruktag area, and the Caledonian sources derived from the Altyn and South Tianshan tectonic belts. 276Ma of age peak records a representative event of Permian large igneous province (LIPs) in the Tarim basin and South Tianshan is likely the major provenance. Indosinian and Cenozoic detrital zircon ages imply that the Beishan block and East Tianshan, even distant Pamir and West Kunlun, were the potential source areas. Due to large scale weathering and leaching, widely exposed K-rich rocks in the periphery of the depression were transported to Lop Nur, providing important materials for the Quaternary potash formation in Lop Nur. In addition, sediment compositions transported by drainage system of the Tarim basin were also major provenance, with limited amount from the orogenic belts in northern and northeastern Lop Nur. The vertical variety features of detrital zircon ages suggest an obvious tectonic uplift in the north part of Lop Nur, probably resulting in the formation of the Luobei depression.