Neoproterozoic (~ 900 Ma) Sariwon sills in North Korea: Geochronology, geochemistry and implications for the evolution of the south-eastern margin of the North China Craton
Neoproterozoic (~ 900 Ma) Sariwon sills in North Korea: Geochronology, geochemistry and implications for the evolution of the south-eastern margin of the North China Craton
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DOI：
10.1016/j.gr.2010.12.011
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发表时间：
2011-07
影响因子：
6.1
通讯作者：
P. Peng;M. Zhai;Qiu-li Li;Fu-guan Wu;Quanlin Hou;Zhong Li;Tiesheng Li;Yanbin Zhang
中科院分区：
文献类型：
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作者：
P. Peng;M. Zhai;Qiu-li Li;Fu-guan Wu;Quanlin Hou;Zhong Li;Tiesheng Li;Yanbin Zhang
沙里院岩床分布于朝鲜半岛中部、华北东部的平南盆地。这些岩床的厚度可达150米，长度可达10公里以上。从一个约50 m厚的岩床中分离出的斜锆石颗粒获得SIMS 206 Pb-207 Pb年龄为899± 7 Ma（MSWD=0.34，n=14），这是该岩床的结晶年龄。同一岩床中的锆石U-Pb年龄截距较低，约为400 Ma，可能与该岩床的绿片岩相变质作用有关。Sariwon岩床为粗粒岩，具有拉斑玄武岩成分。与原始地幔标准化蜘蛛图上的邻近元素相比，它们显示出轻稀土元素浓度（La/YbN=1.4-2.8）的富集，并且高场强元素（例如Nb、Zr和Ti）略有贫乏。整个岩石的εNdt（t= 900 Ma）值约为−2，而锆石颗粒的原位εHft（t= 900 Ma）值则在−25至+8之间。它们与华北平原其他地区的同时代岩床相似，山东半岛徐淮盆地的楚兰岩床和辽东半岛旅大盆地的大连岩床。这些岩床可能起源于亏损的地幔源（例如，而不是来自华北东部的古老岩石圈地幔，并经历了岩石圈物质的显著同化作用。徐淮盆地、旅大盆地和平南盆地的地层和岩床具有可比性，而且根据新元古代的地理重建，三个盆地在地理上是可比较的。因此，我们认为，在新元古代（~ 900 Ma），沿着华北陆块东南缘存在一个徐-怀-吕-大-平南裂谷系，裂谷闭合于~ 400 Ma，是陆缘作用的结果。这是可能的，这东南边缘的NCC没有面对内陆的配置超大陆Rodinia。
The Sariwon sills are distributed in the Pyongnam basin at the center of the Korean peninsula, eastern part of the North China Craton. These sills are up to 150m in thickness and up to more than 10km in length. Baddeleyite grains separated from a ~50m thick sill give a SIMS206Pb–207Pb age of 899±7Ma (MSWD=0.34, n=14), which is interpreted to be the crystallization age of this sill. Zircon grains from the same sill gives a lower intercept U–Pb age of ~400Ma, which is likely a close estimation of the greenschist-facies metamorphism of this sill. The Sariwon sills are dolerites and have tholeiitic compositions. They show enrichment of light rare earth element concentrations (La/YbN=1.4–2.8) and are slightly depleted in high field strength elements (e.g. Nb, Zr, and Ti), in comparison to neighboring elements on the primitive-mantle normalized spidergram. The whole rock εNdt(t=900Ma) values are around −2, whereas in-situ εHft(t=900Ma) values from zircon grains vary from −25 to +8. They are similar to the coeval sills in other parts of the North China Craton, e.g., the Chulan sills (Xu-Huai basin, Shandong peninsula) and the Dalian sills (Lv–Da basin, Liaodong peninsula). These sills possibly originated from a depleted mantle source (e.g., asthenosphere), rather than from the ancient lithospheric mantle of the North China Craton, and have experienced significant assimilation of lithospheric materials. The strata and sills in the Xu-Huai, Lv–Da and Pyongnam basins are comparable; moreover the three basins are geographically correlatable based on Neoproterozoic geographical reconstruction. We therefore propose that there is a Xu-Huai–Lv–Da–Pyongnam rift system along the south-eastern edge of the North China Craton during Neoproterozoic (~900Ma), with the closure of the rift at ~400Ma as a result of a continent-margin process. It is possible that this southeastern margin of the NCC did not face the inland in the configuration of the supercontinent Rodinia.