冀东青龙-双山子地区新太古代高镁安山岩-镁闪长岩锆石U-Pb年代学、地球化学及大地构造意义

Zircon U-Pb Chronology,Geochemistry and Tectonic Significance of Neoarchean High-Mg Andesites and Magnesian Diorites in Qinglong-Shuangshanzi Area,Eastern Hebei

冀东地区位于华北克拉通北缘,学术界对该地区新太古代岩浆作用的成因模式及构造背景一直存在争议,因此对冀东青龙-双山子地区的新太古代变质表壳岩及侵入岩进行了系统的同位素年代学及岩石地球化学研究.锆石LA-MC-ICP-MS U-Pb年代学结果显示变安山岩的形成时代为2 576Ma,辉长闪长岩-英云闪长岩-石英闪长岩的侵入时代为2 484～2 535Ma.岩石地球化学特征显示,较早期的变安山岩部分属高镁安山岩类,源自俯冲板片脱水流体交代地幔楔的部分熔融;而稍晚的侵入岩类为具有埃达克质岩石特征的镁闪长岩类,源区具有熔体交代地幔楔部分熔融的特征;整体构成高镁安山岩-埃达克质镁闪长岩组合.结合区域上的同位素年代学及地球化学报道,冀东青龙-双山子地区新太古代应处于活动大陆边缘构造背景.

Eastern Hebei Province is located in the northern margin of the North China Craton,but magmatic genesis and tectonic setting of Neoarchean igneous rocks in the area still remain controversial.Systematic geochronologic and geochemical study of Neoarchean supracrustal and intrusive rocks in Qinglong-Shuangshanzi area,eastern Hebei are presented in this paper.Zircon LA-MC-ICP-MS U-Pb isotopic dating reveals that the meta-andesite erupted at 2 576 Ma,and the intrusive rocks(gabbro-diorites,tonalites and quartz diorites)emplaced in a range of 2 484 Ma to 2 535 Ma.Part of the early-formed meta-andesites shows high-Mg andesite geochemical characteristics,which indicates these rocks were generated from partial melting of mantle wedge peridotite metasomatised by fluids from dehydration of the subducted slab.The magnesian diorites show adakite characteristics,which suggests they have source characteristics of partial melting of mantle wedge peridotite metasomatised by felsicmelts of the subducted slab.Both of the high-Mg meta-andesites and adakite like magnesian diorites belong to a suite of island arc assemblages.Combining previous regional studies,it is concluded that Qinglong-Shuangshanzi area was under a tectonic setting of active continental margin during Neoarchean era.