华北板块北缘东段中三叠世构造演化——来自辽宁法库地区侵入岩的证据

本文对华北板块北缘东段辽宁北部法库地区中三叠世风歧堡岩体和靠陵沟岩体进行了岩相学、锆石U-Pb年代学、地球化学及Lu-Hf同位素研究。LA-ICP-MS锆石U-Pb测年结果显示，风歧堡岩体和靠陵沟岩体加权平均年龄分别为（241±1） Ma和（243±1） Ma，侵位时代为中三叠世。风歧堡岩体的Ba和Sr质量分数分别为（290.00×10^-6~484.00×10^-6）和（129.00×10^-6~338.00×10^-6），Sr/Y值为13.27~28.17，Sr/Yb值为117.50~250.28；靠陵沟岩体具有较高的Ba质量分数（899.00×10^-6~1 300.00×10^-6）和Sr质量分数（772.00×10^-6~997.00×10^-6），以及较高的Sr/Y值（67.47~78.21）和Sr/Yb值（661.81~781.32），Y、Rb和Yb质量分数较低，分别为11.00×10^-6~14.70×10^-6、55.80×10^-6~78.40×10^-6、1.17×10^-6~1.39×10^-6，地球化学特征上具有高Ba-Sr花岗岩的特征。此外，凤歧堡岩体样品富集大离子亲石元素Rb和K，亏损高场强元素Nb、P、Ti和大离子亲石元素Ba；靠陵沟岩体样品富集大离子亲石元素Ba、K、Sr，亏损高场强元素Nb、P、Ti。凤歧堡和靠陵沟岩体样品Nb/Ta值（4.18~10.26）和Zr/Hf值（30.39~38.76）与地壳平均值相近，Ni、Co和Cr质量分数较低；岩石地球化学特征表明法库地区中三叠世花岗质岩浆源岩为壳源岩石。中三叠世—晚三叠世早期，华北板块北缘东段处于造山地壳加厚阶段。研究区中三叠世花岗岩的ε_Hf（t）值均为正值，亏损地幔二阶段模式年龄（T_DM2）为949~555 Ma，结合岩石地球化学特征，中三叠世花岗质岩浆源岩为造山地壳加厚过程中新元古代新生下地壳部分熔融的产物。

Tectonic Evolution of Northern Margin of Eastern North China Craton:Evidences of Middle Triassic Plutons in Faku Area,Liaoning Province

This paper reports the studies of petrography, zircon U-Pb dating,geochemistry and zircon Lu-Hf isotopic data of the Middle Triassic Fengqipu pluton and Kaolinggou pluton in Faku area in north Liaoning, Northern margin of Eastern North China craton. The LA-ICP-MS zircon U-Pb dating results show that the mean weighted ages of Middle Triassic Fengqipu pluton and Kaolinggou pluton are (241±1) Ma and (243±1) Ma, respectively. The contents of Ba and Sr of Fengqipu pluton are from 290.00×10^-6 to 484.00×10^-6 and from 129.00×10^-6 to 338.00×10^-6, respectively, and the ratios of Sr/Y and Sr/Yb are from 13.27 to 28.17 and from 117.50 to 250.28,respectively. Similar to the geochemistry of high Ba-Sr granites, the samples of Kaolinggou pluton have high Ba and Sr contents, high ratios of Sr/Y and Sr/Yb, and low Rb, Y, and Yb contents. Furthermore, the samples of Fengqipu pluton are enriched in Rb, K(LILE) and depleted in Nb, P, Ti(HFSE) and Ba(LILE), while the samples of Kaolinggou pluton are enriched in Ba, K, Sr(LILE) and depleted in Nb, P, Ti(HFSE). All the sample’s ratios of Nb/Ta and Zr/Hf range from 4.18 to 10.26, from 30.39 to 38.76, respectively, and the samples have low Ni, Co and Cr contents. Geochemecially, the source of Middle Triassic grantic rocks in Faku area was from crust. During the Middle-Late Trassic, Northern margin of Eastern North China craton was under the thickened crustal tectonic setting related to the sustainable orogeny. The Middle Triassic granitic rocks have postive ε_Hf(t) values and 949-555 Ma of two stage model ages, indicating that the magma source of Middle Triassic granitic rocks should be partial melting products of the thickened new-proterozoic lower crust.