摘要
辽北清原地区位于华北板块北缘东段,是研究古太平洋构造域的典型地区之一.研究区中生代岩浆岩的成因及构造背景对认识古太平洋构造域的演化具有重要意义.本次研究对清原夏家堡地区辉长苏长岩、石英闪长岩和花岗闪长岩进行了锆石U-Pb年代学和岩石地球化学分析.锆石U-Pb测年结果表明,辉长苏长岩形成于中侏罗世晚期((163.8±2.4)Ma),石英闪长岩形成于中侏罗世中期((169.9±2.2)Ma),花岗闪长岩形成于中侏罗世中期(169.9～167.3 Ma).岩石地球化学特征上,辉长苏长岩和石英闪长岩属于钙碱性系列岩石,具有低硅、富铝、高镁及较高的Mg#,弱富集轻稀土元素(LREEs),富集Rb、Ba、K、Sr等大离子亲石元素(LILEs),亏损Nb、Ta等高场强元素(HFSEs),Eu呈微弱的正异常或无异常;花岗闪长岩具有较高的硅、铝和全碱含量,具有高钾钙碱性I型花岗岩地球化学特征,Sr/Yb值较高,Eu具弱的负异常,富集LREEs和LILEs(Rb、K、Ba等),亏损HFSEs(Nb、Ta等).上述地球化学特征表明辉长苏长岩和石英闪长岩的原始岩浆应起源于受俯冲板片析出流体所交代的岩石圈地幔部分熔融;花岗闪长岩是俯冲背景下受流体交代的下地壳基性火成岩部分熔融的产物.结合区域构造演化史和区域岩浆活动时空分布规律,认为辽北清原夏家堡地区中侏罗世侵入体的形成与古太平洋板块的俯冲作用有关.
Abstract
Qingyuan area in northern Liaoning,located at the eastern segment of the northern margin of the North China Craton,is one of the typical areas to study the paleo-Pacific ocean tectonic domain.The petrogenesis and tectonic setting of Mesozoic magmatic rocks in the study area are of great significance for understanding the evolution of the paleo-Pacific tectonic domain.This study focuses on the zircon U-Pb geochronology and geochemistry of gabbronorite,quartz diorite and granodiorite in the Xiajiapu area of Qingyuan.Zircon U-Pb dating results show that gabbronorite,quartz diorite and granodiorite were emplaced in the(163.8±2.4)Ma,(169.9±2.2)Ma and 169.9-167.3 Ma respectively.Geochemical characteristics of Gabbronorite and quartz diorite show that they have low SiO2 content,high Al2O3 content and high Mg#value,which are typical of the calc-alkaline series.Samples are weakly enriched in LREEs and enriched in LILEs(e.g.,Rb,Ba,K,Sr)and depleted in HFSEs(e.g.,Nb,Ta,),and Eu shows weak positive or no anomaly;Granodiorite shows a high content of SiO2,Al2O3 and total-alkali,which is typical of the high-K calc-alkaline I-type granite.Samples have high Sr/Yb values and weak Eu negative anomalies,and they are enriched in LREEs and LILEs(e.g.,Rb,K and Ba)and depleted in HREEs and HFSEs(e.g.,Nb,Ta).Based on these data,we conclude that primary magma of gabbronorite and quartz diorite is likely derived from partial melting of lithospheric mantle,which is metasomatized by fluid from subducted oceanic slab.Granodiorite is derived mainly from partial melting of mafic rocks in lower crust,which is metasomatized by fluid.Combining with regional tectonic evolution and spatial distribution of magmatic activity,we suggest that the origin of Middle Jurassic intrusive rocks in Xiajiapu area,Qingyuan,northern Liaoning might be related to the subduction of paleo-Pacific plate.
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