冀北凤山晚古生代闪长岩-花岗质岩石的成因：岩石地球化学、锆石U-Pb年代学及Hf同位素制约  

Petrogenesis of the Late Paleozoic Diorites-Granitoids in Fengshan Area,Northern Hebei Province: Constraints from Petrochemistry,Zircon U-Pb Chronology and Hf Isotope

作　　者：凤永刚[1] 刘树文[1] 吕勇军[1] 田伟[1] 柳小明[2] 

机构地区：[1]造山带与地壳演化教育部重点实验室、北京大学地球与空间科学学院,北京100871 [2]西北大学大陆动力学国家重点实验室,西安710069

出　　处：《北京大学学报（自然科学版）》2009年第1期59-70,共12页Acta Scientiarum Naturalium Universitatis Pekinensis

基　　金：国家自然科学基金(40872120,40821002,40472096,40472118);西北大学大陆动力学国家重点实验室对外开放测试基金资助

摘　　要：冀北风山地区侵位于前寒武纪岩石组合中的晚古生代的闪长岩一花岗质岩石，具有富Na，高Sr，低Y和重稀土元素等地球化学特征，Sr／Y在37．15～151．22之间变化，绝大多数样品均显示正Eu异常（一个样品例外），Eu^＊在0．92～1．53之间变化。LA—ICP-MS锆石U—Pb同位素测年和锆石Hf同位素分析表明闪长岩（JB6024）和二长花岗岩（样品JB6037—1）分别形成于315±2．8Ma和306．6±6Ma，即该区晚古生代存在两个岩浆作用幕。地球化学、全岩Sr-Nd同位素和锆石Hf同位素研究揭示凤山晚古生代闪长岩是EMI型富集岩石圈地幔部分熔融形成的岩浆与古老下地壳部分熔融形成的长英质岩浆混合作用结果，而花岗质岩石则是闪长质岩浆发生分离结晶作用的残余岩浆同化上部地壳岩石形成的。The late Paleozoic diorites-granitoids emplaced into Precambrian lithological assembleges in Fengshan area, Northern Hebei province are characterized by enrichment in sodium （Na2 O/K2O 〉 1.0）, high Sr, low Y and HREE contents, and their St/ Y values change from 37.15 to 151.22. Most samples also show positive Eu anomalies and their Eu^＊ ranges from 0.92 to 1.53. LA-ICP-MS zircon dating and zircon Hf isotope analyses for samples diorite （sample JB6024 ） and monzogranite （sample JB6037-1 ） reveal that the diorite and the monzogranite were produced at 315 ± 2.8 Ma and 306.6 ± 6 Ma, respectively, namely, indicated the two late Paleozoic magmatic episodes in the Fengshan area. Whole rock petroehemistry, Sr-Nd isotopes and zircon Hf isotope indicate that the late Paleozoie Fengshan diorite was produced by the magmatic mixing between marie magma derived from an EMI-type enriched mantle and felsic magma derived from partial melting of the ancient lower crust, and the granitoids derived from fractional crystallization of the dioritic magma that was obviously contaminated by upper crustal materials during their emplacement.

关 键 词：闪长岩和花岗质岩石 锆石U—Pb年代学 Sr-Nd—Hf同位素体系 岩石成因 晚古生代 华北克拉通北缘 

分 类 号：P597[天文地球—地球化学]