| 安徽洪镇地区董岭群碎屑锆石U-Pb年代学及其地质意义 |
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| 引用本文： | 王继林,何斌.安徽洪镇地区董岭群碎屑锆石U-Pb年代学及其地质意义[J].大地构造与成矿学,2016(6):1239-1246. |
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| 作者姓名： | 王继林 何斌 |
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| 作者单位： | 1. 中国冶金地质总局山东局测试中心,山东济南250014;中国地质大学(武汉)地球科学学院,湖北武汉430074;2. 中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广东广州510640 |
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| 基金项目： | 中国科学院知识创新项目(KZCX2YW128;KZCX1YW151)，国家自然科学基金(41173037) |
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| 摘 要： | 安徽洪镇地区的董岭群为一套以二长片麻岩为主的中深变质岩系,长期以来被认为是长江中下游地区古元古代的变质结晶基底,因作为洪镇变质核杂岩的"变质核"而受到广泛关注。为了能够更好地揭示华南前寒武纪的大地构造演化和洪镇"变质核杂岩"的成因,本文对洪镇地区董岭群主体的二长片麻岩进行了碎屑锆石LA-ICP-MS U-Pb定年,获得了760~830 Ma、1930~2060 Ma和2360~2530 Ma 3个主要年龄区间。这一年龄谱与扬子克拉通前寒武纪的碎屑锆石年龄分布特征类似,暗示董岭群的物质源于其附近克拉通物质的剥蚀及搬运;其中最年轻的锆石年龄为768±16 Ma,这一年龄限定了董岭群地层时代下限,结合其上覆盖层为震旦系(底界小于635 Ma),将董岭群的地层时代限定于新元古代,这一结论否定了其为古元古代古老变质结晶基底的说法。综合近年来的研究,扬子板块西缘及东南缘目前并未发现太古宙-古元古代的结晶基底。另外,由于董岭群地层时代的重新厘定,得知这一地区并不存在大规模地层缺失和大规模剥离断层,因此前人提出的洪镇"变质核杂岩"的构造模型值得商榷。
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| 关 键 词： | 董岭群 碎屑锆石U-Pb年龄 新元古代 变质结晶基底 变质核杂岩 |
LA-ICP-MS U-Pb Dating of Detrital Zircons from Dongling Group in Hongzhen Area and its Geological Implications |
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| Abstract: | The Dongling Group,exposed in the Hongzhen area,Anhui province,was previously considered to be the Paleoproterozoic basement.It has been extensively studied because it was believed to be the core of the Hongzhen metamorphic core complex and the metamorphic crystalline basement of South China as well.To accurately interpret the Precambrian tectonic evolution of South China and the formation mechanism of the Hongzhen "metamorphic core complex",detrital zircons from the gneiss,the main part of the Dongling Group,were analyzed and three age groups of 760-830 Ma,1930-2060 Ma and 2360-2530 Ma were obtained.The age distribution of the zircons is similar to those of the Yangtze Craton as whole,indicating that the detrital material of the Dongling Group was derived from adjacent basement of the Yangtze Carton.The youngest detrital zircon age (768±16 Ma) of the Dongling Group and the 635 Ma lower boundary age of overlying Sinian System suggest that the Dongling Group should be deposited in Neoproterozoic rather than Paleoproterozoic.Thus,the Dongling Group is not the crystalline basement of South China.We thus suggest that there is no crystalline basement has yet been discovered in the southeast of the Yangtze Craton.In addition,the strata in the Hongzhen area is continuous so long as the Dongling Group is Neoproterozoic.Therefore,the viewpoints concerning the Hongzhen metamorphic core complex proposed previously need to be re-evaluated. |
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| Keywords: | Dongling Group U-Pb age of detrital zircons Neoproterozoic metamorphic crystalline basement metamorphic core complex |
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