华北克拉通南缘早白垩世中基性火山岩成因及其地质意义  

PETROGENESIS OF THE EARLY CRETACEOUS INTERMEDIATE-MAFIC VOLCANICS FROM SOUTHERN MARGIN OF NORTH CHINA CRATON AND ITS GEOLOGICAL IMPLICATION

作　　者：李晓勇[1,2] 范蔚茗[2,3] 王岳军[2] 夏斌[2] 范立勇[2] 

机构地区：[1]株洲工学院 [2]中国科学院边缘海地质重点实验室,中国科学院广州地球化学研究所,广东广州510640 [3]中国科学院资源环境科学与技术局,北京100864

出　　处：《大地构造与成矿学》2006年第2期220-230,共11页Geotectonica et Metallogenia

基　　金：国家自然科学基金项目(No.40303005);中国博士后科学基金资助项目(No.2004036510)的共同资助.

摘　　要：平顶山早白垩世大营组中基性火山岩样品为钾质和钾玄岩石系列,主要由粗安岩组成,属于偏铝质岩石。低MgO(2.25%~2.88%)和Cr(17.5~30.0μg/g)、Ni(17.4~23.3μg/g),高Al2O3(17.32%~17.56%)和K2O(4.43%~4.56%),K2O/Na2O>1。稀土表现出LREE富集的右倾平滑分布型式,(La/Yb)CN=14.0~14.7,HREE弱分馏,(Gd/Yb)CN=2.42~2.66,富集Rb、Ba、K、LREE和亏损Nb-Ta、Th,弱的Sr正异常。Sr-Nd同位素较富集87Sr/86Sr(t)=0.706877~0.707005,εNd(t)=-10.9^-11.6。大营组中基性火山源区岩的稀土、微量元素地球化学和同位素组成类似于晚中生代苏鲁造山带基性火山岩,北大别镁铁-超镁铁质侵入体和北淮阳中基性火山岩(Fanetal.,2001,2004;Wangetal.,2005),暗示其可能具有相似的岩石成因,即大营组中基性火山来自于古老陆下岩石圈地幔和深俯冲的扬子下地壳混合源区的部分熔融作用,说明华北和扬子陆块在三叠纪碰撞过程中,扬子陆壳深俯冲再循环进入华北岩石圈地幔,其形成与板块俯冲作用没有直接的动力学关系,而形成于陆内伸展拉张环境下。The early Cretaceous volcanics from Pindingshan area, southern margin of North China Craton, show Kenriched and shoshonite characteristics, mainly composed of trachy andesites and belonging to metaluminous rocks. These volcanics show low MgO （2.25% - 2.88% ） , Cr （ 17.5 - 30. 0μg/g） , Ni （ 17.4 - 23.3μg/g） and high Al2O3 （17.32% - 17.56% ） , K2O （4.43% - 4.56% ） contents, with K2O /Na2O 〉 1. They are characterized by strong enrichment in LREE, and K, Ba but depletion in Nb, Ta, Th, and weak positive anomalies in Sr, and show moderately enriched Sr - Nd isotopic compositions （^87Sr/^86Sr （t） = 0. 706877 -0. 707005, εNd （t） = - 10.9 - - 11.6） , similar to those of the volcanics from NHB, the mafic-ultramafic intrusions from North Dabie Complex （NDC） , and basaltic rocks from Sulu Orogen. Such geochemical signatures indicate that the volcanics of Daying Formation may derive from partial melting of hybrid sources between subducted crust of YB and enriched lithospheric mantle of North China Block. The petrogenesis of the volcanics suggests that the YB crust had been deeply subducted and recycled into lithospheric mantle, and that the volcanics were formed under intracontinental extensional regime.

关 键 词：源区混合 地壳再循环 地球化学 早白垩世 大营组 平顶山 华北克拉通南缘 

分 类 号：P588.14[天文地球—岩石学] P591[天文地球—地质学]