西藏洞错地区多尼组砂岩碎屑锆石U-Pb年龄及其地质意义
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摘要
对洞错地区早白垩世多尼组砂岩的碎屑锆石进行了U-Pb测年研究。结果表明,锆石颗粒粒径为50～180μm,Th/U值大,约51颗锆石的比值大于0.4,平均值约为0.64,说明锆石大部分为岩浆成因,部分可能为变质成因;锆石年龄主要分布在7个区间范围(或峰值):3261Ma、2739～2335Ma、1880～1750Ma、1006～657Ma、577～510Ma、456～409Ma和252～202Ma。3261Ma的最老碎屑锆石颗粒说明,其物源区存在古太古代古老地壳的残留。锆石U-Pb年龄谱对应羌塘地块经历的几次构造热事件,验证了洞错地区早白垩世沉积物的物源可能来自北部的南羌塘地块。
In this paper, the authors conducted some researches on U-Pb geochronology of detrital zircon of the Duoni Formation in Dongcuo area, Tibet. The grain diameter of detrital zircon is 50～180μm. The Th/U ratio is high. The Th/U ratio of 51 zircon samples is greater than 0.4, with the typical value being 0.64. So the magmatic zircon is dominant. The distribution of U-Pb age of zircon is 3261 Ma, 2739～2335 Ma, 1880～1750 Ma, 1006～657 Ma, 577～510 Ma, 456～409 Ma and 252～202 Ma. The oldest detrital zircon age is 3261 Ma. The provenance of the sediments contained residues of the earth's crust in Archean.The U-Pb age of zircon corresponds to the tectonic event of Qiangtang. So the provenance of Lower Cretaceous Formation in Dongcuo area should be Qiangtang block.
In this paper, the authors conducted some researches on U-Pb geochronology of detrital zircon of the Duoni Formation in Dongcuo area, Tibet. The grain diameter of detrital zircon is 50～180μm. The Th/U ratio is high. The Th/U ratio of 51 zircon samples is greater than 0.4, with the typical value being 0.64. So the magmatic zircon is dominant. The distribution of U-Pb age of zircon is 3261 Ma, 2739～2335 Ma, 1880～1750 Ma, 1006～657 Ma, 577～510 Ma, 456～409 Ma and 252～202 Ma. The oldest detrital zircon age is 3261 Ma. The provenance of the sediments contained residues of the earth's crust in Archean.The U-Pb age of zircon corresponds to the tectonic event of Qiangtang. So the provenance of Lower Cretaceous Formation in Dongcuo area should be Qiangtang block.
引文
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[16]朱弟成,赵志丹,牛耀龄,等.拉萨地体的起源于古生代构造演化[J].高校地质学报,2012,18(1):1-15.
[2]宋杨,唐菊兴,曲晓明,等.西藏班公湖-怒江成矿带研究进展及一些新认识[J].地质科学进展,2014,29(7):795-809.
[3]Yuan H L,Gao S,Liu X M,et al.Accurate U-Pb age and trace element determinations of zircon by laser ablation-inductively coupled plasma-mass spectrometry[J].Geotandards Geoanalytical Research,2004,28(3):353-370.
[4]吴元保,郑永飞.锆石成因矿物学研究及其对U-Pb年龄解释的制约[J].科学通报,2004,49(16):1589-1604.
[5]Compston W,Williams I S,Kirschvink J L.Zircon U-Pb ages for the Early Cambrian timescale[J].Journal of the Geological Society,1992,149:171-184.
[6]何世平,李荣社,王超,等.青藏高原北羌塘昌都地块发现4.0Ga碎屑锆石[J].科学通报,2011,56(8):573-582.
[7]Windley B F.The Evolving Continents[M].Chichester:John Wiley&Sons,1995:1-526.
[8]王国芝,王成善.西藏羌塘基底变质岩系的解体和时代厘定[J].中国科学(D辑),2001,31(增刊):77-82.
[9]董春艳,李才,万渝生,等.西藏羌塘龙木错-双湖缝合带南侧奥陶纪温泉石英岩碎屑锆石年龄分布模式:构造归属及物源区制约[J].中国科学(地球科学),2011,41(3):299-308.
[10]李江涛,梁斌,何文劲,等.藏北羌塘盆地基底的地质构造演化:来自侏罗纪雁石坪群砂岩碎屑锆石U-Pb同位素年代学证据[J].中国地质,2016,43(4):1216-1226.
[11]Rogers J,Santosh M.Configuration of Columbia,a Mesoproterozoic Supercontinent[J].Gondwana Research,2002,5:5-22.
[12]Zhao G C,Sun M,Wilde S A,et al.A paleo-Mesoproterozoic Supercontinent:Assembly,growth and break up[J].Earth Science Review,2004,67(1/2):93-123.
[13]万天丰.中国大地构造学纲要[M].北京:地质出版社,2003:1-387.
[14]李江涛,梁斌,何文劲,等.藏北羌塘盆地基底的地质构造演化:来自侏罗纪雁石坪群砂岩碎屑锆石U-Pb同位素年代学证据[J].中国地质,2016,43(4):1216-1226.
[15]裴英如,杨竹森,赵晓燕,等.藏北商旭金矿床的碎屑锆石U-Pb年龄及其地质意义[J].地球学报,2017,38(5):711-722.
[16]朱弟成,赵志丹,牛耀龄,等.拉萨地体的起源于古生代构造演化[J].高校地质学报,2012,18(1):1-15.