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刘志慧,罗敏,陈龙耀,曲玮,刘晓春. 2018. 南秦岭佛坪地区地层格架与物源分析:变质沉积岩中碎屑锆石LA-ICP-MS U-Pb定年提供的制约. 岩石学报, 34(5): 1484-1502
南秦岭佛坪地区地层格架与物源分析:变质沉积岩中碎屑锆石LA-ICP-MS U-Pb定年提供的制约
作者单位
刘志慧 中国地质科学院地质力学研究所, 北京 100081
北京大学地球与空间科学学院, 北京 100871 
罗敏 大庆油田有限责任公司第四采油厂地质大队, 大庆 163511 
陈龙耀 中国地质科学院地质力学研究所, 北京 100081 
曲玮 中国地质科学院地质力学研究所, 北京 100081 
刘晓春 中国地质科学院地质力学研究所, 北京 100081 
基金项目:本文受国家重大基础研究发展规划项目(2015CB856104)和国家自然科学基金项目(41472064)联合资助.
摘要:
      南秦岭佛坪地区位于东西秦岭交汇部位,以前寒武纪基底穹状隆升为主要特征,因其特殊的构造位置和变质变形特征而受到广泛关注。为了更好地揭示南秦岭构造带的性质及其在秦岭造山带构造演化中的作用,本文对佛坪地区的前寒武纪基底和沉积盖层进行了系统的碎屑锆石LA-ICP-MS U-Pb年代学研究。佛坪穹隆核部前寒武纪基底中碎屑锆石主要年龄峰值为600~820Ma、2021Ma和2467Ma,其中3个样品给出最年轻的年龄区间约为615~728Ma,沉积时代不早于新元古代,另外1个样品给出的最年轻的年龄峰值为1113Ma,沉积时代不早于中元古代,否定了关于认为其为太古代或古元古代的变质结晶基底的认识,其碎屑物质可能来源于南秦岭构造带和扬子陆块北缘。佛坪穹隆上覆盖层和外围南侧盖层给出了相似的年龄图谱,主要年龄峰值为410~450Ma、650~880Ma和910~950Ma,其中最年轻的年龄区间为344~416Ma,表明其沉积时代晚于泥盆纪,碎屑物质来源为北秦岭构造带和南秦岭构造带。上述研究结果表明,南秦岭构造带(前寒武纪基底)于新元古代已增生为扬子陆块北缘的重要组成部分,于晚古生代(泥盆纪)紧邻华北-北秦岭构造带南缘,并共同为南秦岭大面积的泥盆纪盆地提供碎屑物质。
英文摘要:
      The Foping area in the South Qinling tectonic belt, located at the junction of the East and West Qinling orogen, is characterized by the domal uplifted Precambrian metamorphic basement. Its particular tectonic location and characteristics on metamorphic and deformation have drawn extensive attention. In this paper, systematic LA-ICP-MS U-Pb dating of the detrital zircons from Precambrian basement and Phanerozoic sedimentary covers in the Foping area has been used to reveal the nature of the South Qinling tectonic belt and the role it plays in the tectonic evolution of the Qinling orogen. The age spectrums of detrital zircons from the four Precambrian basement samples in the core of Foping dome show the major populations at 600~820Ma, 2021Ma and 2467Ma. Three of the samples show a youngest population range of 615~728Ma, suggesting the deposition time is no earlier than the Neoproterozoic. While the other one has the youngest population at 1113Ma, suggesting the deposition time is no earlier than the Mesoproterozoic. Thus, the Precambrian metamorphic basement of the Foping dome is not formed in the Archean or Paleoproterozoic, its sediments might derive from the South Qinling tectonic belt and the northern margin of Yangtze Block. Sedimentary covers in Foping dome and its peripheral strata display similar age spectrums. The youngest populations range from 342~416Ma, and the major populations show three ranges of 410~450Ma, 650~880Ma and 910~950Ma. These data suggest that the sedimentary covers deposited after the Devonian, and sediments were probably derived from the North and South Qinling tectonic belt. Based on those analyses above, we propose that the South Qinling tectonic belt accreted to the northern margin of the Yangtze Block in the Neoproterozoic, and was adjacent to the southern margin of the North China Block-North Qinling tectonic belt in the Paleozoic. The North and South Qinling tectonic belt provided the clastic sediments to the widespread Devonian basins.
关键词:碎屑锆石  LA-ICP-MS U-Pb定年  物质来源  变质沉积岩  佛坪地区
投稿时间:2017-11-05  修订日期:2018-03-02
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