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首页> 外文期刊>Journal of Asian earth sciences >SHRIMP U-Pb ages of detrital zircons in metasedimentary rocks of the central Ogcheon fold-thrust belt, Korea: Evidence for tectonic assembly of Paleozoic sedimentary protoliths
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SHRIMP U-Pb ages of detrital zircons in metasedimentary rocks of the central Ogcheon fold-thrust belt, Korea: Evidence for tectonic assembly of Paleozoic sedimentary protoliths

机译：韩国Ogcheon褶皱冲断带中生沉积岩中碎屑锆石的SHRIMP U-Pb年龄：古生代沉积原生质体构造组合的证据

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We analyzed detrital zircons in four metasandstones and two metadiamictites of the central Ogcheon Metamorphic Belt (OMB) in order to provide geochronologic constraints on the time of deposition and protolith age distributions. SHRIMP U-Pb ages of the newly analyzed zircons range from Archean to Early Paleozoic, and their age patterns permit the definition of four lithotectonic slices: upper and lower Pibanryeong units consisting primarily of quartzite and metasandstone; an upper Poeun unit of black slate containing Early Permian plant fossils; and a lower Poeun unit made up of metasandstone and metadiamictite. A quartzite of the upper Pibanryeong unit yielded two major zircon age populations at 965 ± 11 Ma and 447 ± 5 Ma, whereas two lower Pibanryeong metasandstones show major age concentrations at ~2.5Ga, 1.0-0.9 Ga, and 545-535 Ma. The youngest components of these units suggest maximum ages of sedimentation as Late Ordovician and Early Cambrian, respectively. These upper and lower Pibanryeong zircon age distribution patterns are consistent with those of Ordovician and Devonian sedimentary strata, respectively from the South China Craton (SCC). On the other hand, three samples of the lower Poeun unit yielded two distinct age populations at ~1.87 Ga and 755 ± 7 Ma. In addition, a metadiamictite contains abundant Mesoproterozoic zircons with two broad peaks centered at ~1.3 and 1.6 Ga. Protolith ages and distribution patterns are profoundly different between the Pibanryeong and Poeun lithotectonic packages, suggesting the presence of a major thrust fault juxtaposing allochthons that are also characterized by large P-T contrasts. Our detrital zircon results for the Pibanryeong unit are compatible with derivation from the SCC, in apparent contrast with the Poeun occurrence of Early Permian plant fossils most likely correlative with the North China Craton (NCC). Taken together, the suturing of Paleozoic metasedimentary terranes in the OMB is a product of Permo-Triassic orogeny reflecting collision of the North and South China cratons.
机译：我们分析了Ogcheon中央变质带（OMB）中部的4个变砂岩和2个变质岩中的碎屑锆石，以便为沉积时间和原生岩年龄分布提供地质年代学约束。新近分析的锆石的SHRIMP U-Pb年龄范围从太古宙时代到早古生代，它们的年龄模式可以定义四个岩相构造切片：上和下Pibanryeong单元主要由石英岩和准砂岩组成；黑色板岩的上Poeun单元，其中包含早二叠世的植物化石；下部的Poeun单元由变质砂岩和变质透辉石组成。 Pibanryeong上部单元的一个石英岩在965±11 Ma和447±5 Ma上产生了两个主要的锆石年龄种群，而两个下Pibanryeong阶砂岩在〜2.5Ga，1.0-0.9 Ga和545-535 Ma处显示了主要的年龄集中。这些单元中最年轻的部分表明最大的沉积年龄分别为奥陶纪晚期和寒武纪早期。这些上，下Pibanryeong锆石年龄分布模式分别与华南克拉通（SCC）的奥陶纪和泥盆纪沉积地层一致。另一方面，较低的Poeun单位的三个样本在〜1.87 Ga和755±7 Ma处产生了两个不同的年龄种群。此外，变质岩中含有丰富的中元古代锆石，在约1.3和1.6 Ga处有两个宽峰。原生岩年龄和分布模式在Pibanryeong和Poeun岩相构造包中有很大的不同，这表明存在一个主要的逆冲断层，并排排列了所有的外原体。 PT对比度大。我们对Pibanryeong单元的碎屑锆石结果与SCC的推导相吻合，这与Poeun发生的早二叠世植物化石极有可能形成鲜明对比，后者可能与华北克拉通（NCC）有关。综上所述，OMB中的古生代准沉积地层的缝合是二叠纪-三叠纪造山运动的产物，反映了华北和华南克拉通的碰撞。

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