塔里木柯坪地区二叠系沉积岩碎屑锆石U-Pb定年和Hf同位素特征及其对塔里木块体地质演化的限定

U-Pb dating and Hf isotopic compositions of detrital zircons from Permian sedimentary rocks in Keping area of Tarim Basin,Xinjiang,China: Constraints on geological evolution of Tarim Block

塔里木早二叠世大火成岩省是我国继峨眉山大火成岩省得到国际公认后的又一个重要的大火成岩省，对其中广泛出露的多层玄武质熔岩的夹层沉积岩中的锆石年代学和Hf同位素特征研究可以对塔里木早二叠世大火成岩省的岩浆演化以及之前的地质史方面的认识提供重要的信息。本文选取塔里木西北缘柯坪地区印干村大湾沟剖面玄武岩的夹层粉砂岩中3个不同层位的沉积岩样品，对其中碎屑锆石u-Ph年龄和Hf同位素组成进行了较系统的研究。研究表明3个样品碎屑锆石u-Pb年龄中最年轻的一组年龄峰值介于284～291Ma之间，与前人对塔里木早二叠世大火成岩省大规模溢流玄武质岩浆事件相吻合。此外，还存在老于1．7Ga、0．9～1．0Ga和750～850Ma以及410～450Ma的几组年龄，可能分别对应于塔里木哥伦比亚超大陆聚合、罗迪尼亚超大陆的聚合和裂解以及志留系地层的剥蚀沉积等一系列地质事件的发生。对上述3个沉积岩样品中锆石Hf同位素成分分析得出其碎屑锆石源区成分复杂，主要源自塔里木前寒武纪基底、志留系地层和塔里木早二叠世大火成岩省岩浆事件。具有二叠纪年龄的锆石εhf（t）值在-10～4之间，平均值为-4．8，Hf同位素亏损地幔模式年龄tDM^HF为801～1363Ma，表明这些玄武质熔岩中沉积岩夹层的碎屑锆石应该来自古老的富集岩石圈地幔。通过对柯坪地区这些夹层沉积岩的锆石u-Pb年龄和Hf同位素成分研究，有助于对塔里木早二叠世大火成岩省岩浆演化的认识。

The Early Permian Tarim Large Igneous Province （TLIP） is regarded as an important large igneous province in China. Study of the geochronology and Hf isotopic compositions of detrital zircons from sedimentary rocks as intedayers of large-scale flood basaltic lavas can provide important implication on the magmatic evolution of TLIP. Three samples from the different sedimentary layers in laminated siltstones among the basalts of the Yingan section in Keping area of Tarim Basin were selected for the U-Pb dating analysis of Hf isotopic compositions of detrital zircons using LA-MC-ICP-MS analyses. Three samples of sedimentary rocks yielded the youngest peak age ranging between 284Ma and 291Ma, coincided with the geological event of the Early Permian TLIP reported previously. In addition, there are other age clusters of 410 ～450Ma, 750 ～ 850Ma, 0. 9 ～ 1.0Ga and older than 1.7Ga, probably corresponding to the Tarim Silurian strata denudation and sediment, breakup and assembly of Rondina supercontinent, and assembly of Columbia supercontinent respectively. Based on the analyses of zircon Hf isotopic compositions of three sedimentary rock samples, the source materials of detrital zircons are complicated, mainly from the Precambrian basement, Silurian strata and Early Permian TLIP. The εHf（t） value of Permian zircons was -10-4 with the average value of -4. 8, and the tDM^Hf（depleted- mantle model age） of Hf isotopes between 1363Ma and 801Ma were yielded, illustrating that detrital zircons may be from the old enrichment lithosphere mantle. The study of zircon U-Pb geochronology and Hf isotopic compositions from these sedimentary rocks provided the better understanding of the Early Permian TLIP magmatic evolution