冀东青龙地区中生代花岗岩的岩石成因和地质意义  

Petrogenesis and geological implications for the Mesozoic granites in Qinglong area,eastern Hebei Province

作　　者：徐希阳 姜能[1] 范文博[1,2] 胡俊[1,2] 宗克清[3] 

机构地区：[1]中国科学院地质与地球物理研究所,岩石圈演化国家重点实验室,北京100029 [2]中国科学院大学地球科学学院,北京100049 [3]中国地质大学地质过程与矿产资源国家重点实验室,武汉430074

出　　处：《岩石学报》2016年第1期212-232,共21页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(90914008)资助

摘　　要：冀东青龙地区中生代发育多期花岗质岩浆活动。本文系统报道了青龙地区三叠纪都山花岗岩和侏罗纪白家店花岗岩及其镁铁质微粒包体(MMEs)的锆石U-Pb年龄、地球化学和Sr-Nd-Hf同位素组成。锆石SIMS U-Pb定年结果显示,都山花岗岩的结晶年龄为215.7±2.3Ma,指示了晚三叠世岩浆活动;而白家店花岗岩及其包体的结晶年龄分别为170.5±2.0Ma和172.4±2.0Ma,指示了中侏罗世岩浆活动。都山花岗岩以低含量的MgO、Fe_2O_3~T、Cr和Ni,高(La/Yb)_N、Sr/Y比值及低Yb和Y含量,低的初始^(87)Sr/^(86)Sr比值(0.7042~0.7044)、极负的ε_(Nd)(t)值(-19.8^-14.4),很负的ε_(Hf)(t)值(-17.6^-13.0,除了2个较大值-5.6和-8.6)和接近晚太古代的Hf模式年龄,显示出主要来源于晚太古代下地壳重熔,可能有少量幔源物质加入。综合的岩石学、矿物学、地球化学和Sr-Nd-Hf同位素数据(白家店花岗岩:(^(87)Sr/^(86)Sr)_i=0.7051~0.7065,ε_(Nd)(t)=-13.4^-10.8,ε_(Hf)(t)=-11.8^-8.2;MMEs:(^(87)Sr/^(86)Sr)_i=0.7059~0.7062,ε_(Nd)(t)=-11.1^-7.0,ε_(Hf)(t)=-3.7^+3.4),表明了白家店花岗岩和MMEs为亏损地幔来源的镁铁质岩浆和下地壳来源的长英质岩浆通过混合形成。从晚三叠世都山花岗岩到中侏罗世白家店花岗岩,它们成因的明显差异,揭示了地幔角色的转换(从只提供热量几乎不提供物质到既提供能量又提供物质),暗示华北东部岩石圈在这一时期可能发生一次重要减薄。Multiple episodes of granitic magmatism occurred during Mesozoic in Qinglong area, eastern Hebei Province. This study presents a systematic zircon U-Pb ages, geochemical and Sr-Nd-Hf isotopic compositions of Triassic Dushan granites and Jurassic Baijiadian host granites and its mafic microgranular enclaves （MMEs）. SIMS U-Pb dating of zircons yields a concordant age of 215.7 ±2. 3Ma for the Dushan granite and two nearly consistent crystallization ages of 170. 5 ±2. 0Ma and 172.4 ±2. 0Ma for the Baijiadian granite and its MME, suggesting two episodic granitic magmatism occurred in the Late Triassic and the Middle Jurassic, respectively. Dushan granites have low contents of MgO, Fe2 03 T, Cr and Ni, high ratios of （La/Yb） N and Sr/Y but low contents of Yb and Y, low ratio of initial S7Sr/S6Sr （0. 7042 -0. 7044 ） and extremely negative value of εNd （t） （ -19. 8 - --14. 4 ）, highly negative value of of（t） （ -17.6 - -13.0）, except two relatively negative value of -5.6 and -8. 6, and the hafnium model age approximate the Late Archean, suggesting the granite derived dominantly by partial melting of the Late Archean lower crust, with the involvement of minor mantle material. Integrated data of petrological, mineralogical, geochemical and Sr-Nd-Hf isotopic compositions （ Baijiadian granites ： （ s7 Sr/S6 Sr）i= 0. 7051 - 0. 7065, 8Nd （t） = - 13. 1 - 11. 2, εHf （ t ） = - 11. 8 - 8. 2 ; MMEs ： （ 87 Sr/86 Sr）i = 0. 7059 - 0. 7062, εNd （t） = - 11. 1 - 7. 0, 6He （t） = - 3. 7 - ＋ 3. 4 ）, indicates that the Baijiadian granites and MMEs were generated by mixing of the depleted mantle-derived mafic magma with the lower ernst-derived felsie magma. The different petrogenesis for the Late Triassic Dushan granites and Middle Jurassic Baijiadian granites, suggests that the mantle played different roles in the granitic magmatism formation （from providing heat with a little or without material to providing heat and material）, implying an important lithospheric thinning

关 键 词：中生代 花岗岩 岩石成因 岩浆混合 岩石圈减薄 青龙地区 冀东 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]