青藏高原东北缘寺口子剖面碎屑锆石示踪及其构造意义
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本文为国家自然科学基金(41202148, 41030317)、中国地震局地震行业专项(201008003)和地质研究所基本科研业务专项(IGCEA1127)共同资助的成果。


Provenancial Tracing for the Cenozoic Sikouzi Section in the NortheasternMargin of the Tibetan Plateau and Its Tectonic Implications
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    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200~470 Ma(以230 Ma、440 Ma为峰值年龄)、1600~1890 Ma、2100~2450 Ma,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720~980 Ma的年龄峰值;4 Ma的砂岩样品中锆石U Pb年龄谱主要为200~490 Ma。这些样品中,1600~1890 Ma与2100~2450 Ma的锆石εHf(t)值偏负(-31.1~5.1),720~980 Ma的锆石具有负的εHf(t)值为-15.1~-1.7, 200~470 Ma的锆石εHf(t)值范围较宽为-11.2~12.5。通过与周围构造单元对比,发现1600~1890 Ma与2100~2450 Ma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200~470 Ma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27 Ma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。

    Abstract:

    Located in the northeastern corner of the Tibetan Plateau, the Sikouzi section deposits huge thick Cenozoic strata whose provenancial 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 200~470 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 εHf(t) values, the 720~980 Ma zircons have positive εHf(t) values ranging from -15.1~-1.7, and the 200~470 Ma zircons have εHf(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.

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王伟涛,郑德文,庞建章.2013.青藏高原东北缘寺口子剖面碎屑锆石示踪及其构造意义[J].地质学报,87(10):1551-1569.
Wang Weitao, Zheng Dewen, Pang Jianzhang.2013. Provenancial Tracing for the Cenozoic Sikouzi Section in the NortheasternMargin of the Tibetan Plateau and Its Tectonic Implications[J]. Acta Geologica Sinica,87(10):1551-1569.

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  • 收稿日期:2012-11-20
  • 最后修改日期:2013-02-25
  • 录用日期:2013-10-28
  • 在线发布日期: 2013-10-30
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