东北延边地区显生宙地壳增生和改造过程的Nd-Hf-O同位素制约
发布时间：2018-10-07 21:25
【摘要】：延边地区位于华北克拉通、兴蒙造山带和俄罗斯远东锡霍特-阿林活动大陆边缘之间,自古生代以来经历了古亚洲洋、古太平洋甚至太平洋板块俯冲作用的影响,这些不同时期的大洋俯冲、消减导致了区域上发生了强烈的地壳增生和改造作用,是探讨大陆地壳增生、改造、再循环甚至置换作用的天然实验室。花岗岩作为地壳的熔融产物,势必记录了区域地壳的形成和演化过程。论文选择延边地区广泛发育的晚古生代-早白垩世花岗岩为研究对象,通过岩石学、主、微量元素、Sr-Nd同位素以及锆石原位/微区Hf-O同位素的联合研究,取得了以下主要研究成果和进展。(1)综合的花岗岩元素-同位素对比结果显示延边地区以富尔河-古洞河断裂为界可以划分为南、北两个岩区。在北区,白垩纪之前形成的花岗岩显示亏损、年轻的源区特征(εNd(t)=㧟0.1~㧏3.8,平均值为2.4;TDM2=691~976 Ma,平均值为795 Ma;锆石εHf(t)=㧟2.5~㧏14.6,平均值为㧏9.0,TDM2=330~1388Ma,平均值为666 Ma;δ18O=3.4~8.7‰,平均值为5.60±0.36‰),反映其熔融源区主要为新增生的年轻地壳组分。在南区,白垩纪之前形成的花岗岩则显示相对富集的物质组成特点(εNd(t)=㧟13.6~㧟0.6,TDM2=1004~2166 Ma;锆石εHf(t)=㧟25.8~㧏8.5,TDM2=663~2906 Ma;δ18O=4.9~10.2‰),反映其熔融源区中存在古老再循环的华北克拉通地壳组分。(2)区域内花岗岩的熔融源区包含了至少三种地壳组分:古亚洲洋型增生弧地壳、古太平洋型增生弧地壳和华北克拉通古老再循环地壳。在古亚洲洋增生地壳组分中存在高锆石εHf(t)(㧏11.5~㧏14.6)和低?18O(5.5‰)的端元,很可能为构造侵位于地壳深部的残留高温蚀变洋壳。(3)从二叠纪到白垩纪,北区花岗岩全岩εNd(t)和锆石εHf(t)值随着侵位年龄的变新而逐渐降低,而锆石的?18O值显示逐渐升高的趋势,南区花岗岩的变化趋势正好相反,在早白垩世两区的Nd-Hf-O同位素组成趋于一致,反映先存于北区的古亚洲洋型增生弧地壳和南区的华北克拉通古老再循环地壳,在中生代期间遭受古太平洋板块俯冲形成的新生弧地壳的强烈改造和置换作用。(4)延边地区显生宙的地壳演化可以划分为四个演化阶段:(a)290-250 Ma为古亚洲洋俯冲导致的地壳增生阶段,岩石类型主要为高钾钙碱性花岗岩;(b)240-210 Ma为古亚洲洋俯冲板片断离的陆内伸展阶段,深部地壳发生重熔形成大量的碱性花岗岩;(c)190-160 Ma,古太平洋俯冲-改造阶段,形成了大量高钾钙碱性花岗岩;(d)130-110 Ma,古太平洋俯冲后撤阶段,形成了钙碱性花岗岩和火山岩。
[Abstract]:The Yanbian area is located between the North China Craton, the Xingmeng orogenic belt and the active continental margin of Sikhot-Arlin in the Russian far East. Since Paleozoic, the Yanbian area has experienced subduction of the paleo-Asian ocean, paleo-Pacific and even Pacific plate. The subduction and subduction of the ocean in these different periods lead to strong crustal accretion and transformation in the region, which is a natural laboratory for the exploration of continental crustal accretion, transformation, recycling and even replacement. Granite, as the melting product of the crust, is bound to record the formation and evolution of the regional crust. The late Paleozoic and early Cretaceous granites widely developed in Yanbian area were selected as the research objects. The combined studies of petrology, main elements and trace elements such as Sr ND isotopes and zircon in situ / microregional Hf-O isotopes were carried out. The main research results and progress are as follows: (1) the comprehensive comparison of elements and isotopes of granite shows that Yanbian area can be divided into two rock areas in the south and north by Fuhe-Gudong River fault. In the northern region, pre-Cretaceous granites show depleted, young source characteristics (蔚 Nd (t)? 0.1? The average value of Ma, is 2.4TDM2TDM2O691 / 976 Ma, and the average value is 795 Ma; zircon 蔚 Hf (t)? 2.5? 14.6, average? The average value is 666 Ma; 未 18O=3.4~8.7 鈥，
本文编号：2255725
[Abstract]:The Yanbian area is located between the North China Craton, the Xingmeng orogenic belt and the active continental margin of Sikhot-Arlin in the Russian far East. Since Paleozoic, the Yanbian area has experienced subduction of the paleo-Asian ocean, paleo-Pacific and even Pacific plate. The subduction and subduction of the ocean in these different periods lead to strong crustal accretion and transformation in the region, which is a natural laboratory for the exploration of continental crustal accretion, transformation, recycling and even replacement. Granite, as the melting product of the crust, is bound to record the formation and evolution of the regional crust. The late Paleozoic and early Cretaceous granites widely developed in Yanbian area were selected as the research objects. The combined studies of petrology, main elements and trace elements such as Sr ND isotopes and zircon in situ / microregional Hf-O isotopes were carried out. The main research results and progress are as follows: (1) the comprehensive comparison of elements and isotopes of granite shows that Yanbian area can be divided into two rock areas in the south and north by Fuhe-Gudong River fault. In the northern region, pre-Cretaceous granites show depleted, young source characteristics (蔚 Nd (t)? 0.1? The average value of Ma, is 2.4TDM2TDM2O691 / 976 Ma, and the average value is 795 Ma; zircon 蔚 Hf (t)? 2.5? 14.6, average? The average value is 666 Ma; 未 18O=3.4~8.7 鈥，
本文编号：2255725
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