河北承德甲山正长岩成因的Sr-Nd-Pb-Hf同位素制约  

Petrogenesis of the Jiashan syenite in Chengde, Hebei Province: Geochemical and Sr-Nd-Pb-Hf isotopic evidence

作　　者：刘源[1] 江思宏[2] 陈春良[2,3] 韩宁[2] 

机构地区：[1]中国地质大学,湖北武汉430074 [2]中国地质科学院矿产资源研究所,国土资源部成矿作用与资源评价重点实验室,北京100037 [3]中国地质大学,北京100083

出　　处：《岩石矿物学杂志》2015年第1期14-34,共21页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金资助项目(41030421,41273061)

摘　　要：报道了华北克拉通北缘承德地区甲山正长岩的锆石U-Pb年龄及Hf同位素、主微量元素、Sr-Nd-Pb同位素组成。甲山岩体的LA-ICP-MS锆石U-Pb年龄为111~108 Ma,代表岩体的结晶年龄,表明其侵位于早白垩世晚期。岩体高Si O2、K2O+Na2O、Al2O3、LILEs(Rb、K)和LREE,低Fe2O3T、Ca O、Ti O2、Mg O和HFSE,具有板内裂谷岩浆岩的特征,属A型花岗岩。甲山岩体εNd(t)=-5.0^-0.9,tDM2(Nd)=0.98~1.31 Ga;εHf(t)=-2.7^+4.3,tDM2(Hf)=0.90~1.33 Ga;Δ8/4=84.9~91.3,Δ7/4=-6.4^-4.0,(206Pb/204Pb)i=16.63~17.10,(207Pb/204Pb)i=15.24~15.30,(208Pb/204Pb)i=36.54~37.20。根据野外地质观察、实验岩石学以及元素地球化学和Sr-Nd-PbHf同位素示踪的综合分析,认为甲山岩体可能起源于下地壳与亏损地幔的混合源区,是华北克拉通北缘岩石圈强烈减薄、地壳伸展作用的结果。早白垩世甲山岩体形成过程中亏损地幔物质的参与指示了华北克拉通北缘岩石圈减薄和软流圈地幔上涌,记录了陆内伸展环境下与软流圈底侵作用相关的岩浆事件。The LA-ICP-MS zircon U-Pb ages and Hf isotopic data, major and trace elements and Sr-Nd-Pb iso- topic compositions are presented in this paper for the Jiashan syenite intrusive on the northern margin of the North China Craton. The Jiashan syenite intrusive was emplaced at 111--108 Ma in the Early Cretaceous peri- od. The pluton has high SiO2, KO2^＋ Na2O, Al2O3, LILEs （Rb, K） and LREE but low Fe2O3^T, CaO, TiO2, MgO and HFSE, with no Nb and Ta anomalies, suggesting intracontinental rift volcanic rocks that belong to the A-type granite, eNd（t） = - 5.0-- - 0.9, tDM2（Nd） = 0.98-- 1.31 Ga, εHf（ t ） = - 2.7～ ＋ 4.3, tDM2（Hf） = 0.90～1.33 Ga, A8/4 = 84.9～91.3, A7/4 = - 6.4～- 4.0, （206pb/204pb）i = 16.63～ 17.10, （^207pb/^204pb）i = 15.24～15.30, and （^208pb/^204pb）i = 36.54～ 37.20. According to the comprehensive analysis of the geologi- cal field observation, experimental petrology, trace element geochemistry and Sr-Nd-Pb-Hf isotopes, the authors hold that the Jiashan pluton was derived from the mixed source of the lower crust and the depleted mantle, and resulted from the crustal extension and the lithosphere thinning of the NCC. The involvement of the depleted mantle during the formation of the Early Cretaceous Jiashan syenite intrusive indicates the lithospheric thinning on the northern margin of the North China Craton and the upwelling of the asthenosphere mantle, which record- ed the magmatic events related to the asthenosphere underplating in a continental extensional environment.

关 键 词：正长岩 早白垩世 下地壳 亏损地幔 甲山岩体 华北克拉通 

分 类 号：P588.122[天文地球—岩石学] P597[天文地球—地质学]