青藏高原东北缘寺口子剖面碎屑锆石示踪及其构造意义  

Provenancial Tracing for the Cenozoic Sikouzi Section in the Northeastern Margin of the Tibetan Plateau and Its Tectonic Implications

作　　者：王伟涛[1] 郑德文[1] 庞建章[1] 

机构地区：[1]中国地震局地质研究所,地震动力学国家重点实验室,北京100029

出　　处：《地质学报》2013年第10期1551-1569,共19页Acta Geologica Sinica

基　　金：国家自然科学基金(41202148,41030317);中国地震局地震行业专项(201008003);地质研究所基本科研业务专项(IGCEA1127)共同资助的成果

摘　　要：位于青藏高原东北缘的寺口子剖面发育巨厚的新生代沉积地层,分析这些沉积物的碎屑来源能够为高原东北缘构造变形过程提供重要证据。本文在寺口子剖面磁性地层年代的约束下,对该剖面27~4 Ma的砂岩样品进行了碎屑锆石示踪研究。研究结果显示27~12 Ma的砂岩样品中锆石U-Pb年龄主要分布在200~470Ma(以230Ma、440Ma为峰值年龄)、1600~1890Ma、2100~2450Ma,与>12 Ma的砂岩样品相比,7 Ma的砂岩样品中新增了锆石U-Pb年龄为720~980Ma的年龄峰值;4Ma的砂岩样品中锆石U-Pb年龄谱主要为200~490Ma。这些样品中,1600~1890Ma与2100~2450Ma的锆石εHf(t)值偏负(-31.1~5.1),720~980Ma的锆石具有负的εHf(t)值为-15.1^-1.7,200~470Ma的锆石εHf(t)值范围较宽为-11.2~12.5。通过与周围构造单元对比,发现1600~1890Ma与2100~2450Ma的锆石可能源于与鄂尔多斯地块西缘,720~980 Ma的锆石与宁夏中部的南华山、西华山岩石具有亲缘性,U-Pb年龄为200~470Ma的锆石则与六盘山南部岩浆岩的锆石U-Pb年龄一致。寺口子剖面碎屑锆石示踪与半定量估算表明:六盘山南部可能在27Ma已隆升、变形,成为宁夏南部盆地的物源区,而宁夏南部盆地晚中新世的物源变迁可能反映了海原-六盘山断裂带强烈的构造变形。Located in the northeastern corner of the Tibetan Plateau, the Sikouzi section deposits huge thick Cenozoic strata whose provenancia analysis provides the exceptional opportunity to testify the deformational processes in the northeast Tibetan Plateau. Here, the single grain detrial zircon U Pb ages and Hf isotopic compositions are used to trace the source variation of the 27-4 Ma strata based on the Magnetostragraphy from the Sikouzi section. Most of the U-Pb ages from 27-12 Ma samples concentrate within the intervals of 200-70 Ma （clustering around two peak ages of 230 Ma and 440 Ma）, 1600-1890 Ma, 2100-2450 Ma. In contrast to the 27--12 Ma samples, 7 Ma sample has one more detrital zircon age peak of 720-980 Ma, and zircons from the sample with age of 4 Ma is dominated by U-Pb ages in range of 200-490 Ma. In the samples collected from the Sikouzi Section, the 1600-1890 Ma and 2100-2450 Ma zircons mainly have positive au-（t） values, the 720-980 Ma zircons have positive s,-（t） values ranging from --15.1--1.7, and the200-470 Mazirconshave-Hf（t） values of --11.2 to 12.5. Comparing these with neighboring tectonic units, we found that zircon populations at 1600-1890 Ma, 2100-2450 Ma probably were drained from west margin of Ordos block, the 720-980 Ma zircons have their affinity to the Xihuashan and Nanhuashan and zircons at 200-470 Ma may come from west Liupanshan. The results of zircon source trace suggest that the southern Liupanshan probably initiate uplift at - 27 Ma and late Miocene deformation and uplift in this region may related to reactivation of Haiyuan-Liupansh fault system.

关 键 词：锆石U-PB年龄 HF同位素组成 寺口子剖面 青藏高原东北缘 

分 类 号：P597[天文地球—地球化学] P548[天文地球—地质学]