大兴安岭南段东麓中生代O型埃达克质火山岩及其成因、古构造环境和找矿意义  

Mesozoic O-type adakitic volcanic rocks and its petrogenesis,paleo-tectonic dynamic and nineralization significance of the eastern side of sourthern Da Hinggan,China.

作　　者：张永北[1] 孙世华[1] 毛骞[1] 

机构地区：[1]中国科学院地质与地球物理研究所矿物资源重点实验室

出　　处：《岩石学报》2006年第9期2289-2304,共16页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2003CB716506);中国地质大学(武汉)(40472037);北京大学(40372103)自然科学基金项目.

摘　　要：蒙东西拉禾伦河北侧查干木伦河流域,属中生代大兴安岭火山-侵入杂岩带南段。最近区内晚侏罗世满克头鄂博组陆相火山杂岩火山盾中,发现有埃达克质火山岩,与少量钠质流纹岩和玄武岩共生。埃达克岩 Al_2O_3>15%,MgO<3.4%,K_2O 平均=1.77%,Na_2O/K_2O>1,LREE 富集,HREE 及 LIRE 强烈亏损,无负铕异常,高 Sr(497.91～896.40×10^(-6)),低 Y(4.33～15.77<18×10^(-6)),低 Yb(0.35～1.54<1.9×10^(-6)),I_(Sr)=0.70374～0.70594,ε_(Nd)(t)为-0.45～+6.58,在 K-Na-Ca、Rb-Sr-Ba、Sr/Y-Y 和 Sr/Yb-Yb 等图中属埃达克岩,具奥长花岗岩演化趋势,是典型的 O 型埃达克岩。其与共生岩石ε_(Nd)(t)、I_(Sr)与晚古生代玄武岩的接近,部分岩石 t_(DM)(677～845Ma)与晚古生代俯冲洋壳(t_(DM)=627～998Ma)相同,Sr-Nd 同位素及Zr/Hf-Nb/Ta 比值具有亏损地幔与下地壳混合特征,另有岩石(t_(DM)=343～453Ma)源于古生代年轻地幔。据此推论其源岩是以晚元古代俯冲洋壳为主,多源物质混合的增生地体下地壳。La_N/Yb_N-Yb_N 及 La/Sm-La 图证明埃达质岩浆是榴辉岩化源岩部分熔融的原始岩浆,钠质流纹岩是该原始岩浆分离结晶产物,玄武岩浆则可能是源岩深度熔融的结果。岩石成分及微量元素判别该火山活动环境是大陆边缘弧。大兴安岭地区在中生代出现埃达克质火山岩及该类火山弧,未必与环太平洋或者鄂霍茨克海俯冲构造直接相关,而是晚古生代古亚洲洋残存洋壳在中生代沿续存俯冲断裂继续向增生地体下地壳俯冲并发生部分熔融结果。区内与满克头鄂博组有关的铁、铜、金矿化,应有大矿前景。The valley of Chagan Mulun River on the north side of Xila Mulun fiver in eastern Mongolian, is the east side of southern Da Hinggan Mesozoic volcano-platonic complex zone. Recently, many adakitic volcanic rocks with a little intergrowth of sodium rhyolite and basalt have been discovered in the Neo-mesozoic Manketou Obo volcanic group in this area. Of the adakite, Al2O3 〉15%, MgO 〈3.4%, average K2O = 1.77 %, Na2O/K2O 〉 1, LREE enriched, but HREE and LITE greatly depleted, lack negative Eu anomaly, high Sr （497. 91 ×10^ -6- 896.40 ×10^-6 ）, low Y（4. 33× 10^-6 -15. 77 ×10^-6 〈 18 ×10^ -6 ） , lOW Yb（0.35× 10^-6 - 1.54 ×10^ -6 〈 1.9 ×10^ -6） , ISr = 0. 70374 - 0. 70594, εNd （t） = - 0. 45 - ＋ 6. 58. In K-Na-Ca, Rb-Sr-Ba, Sr/Y-Y and Sr/Yb-Yb diagram, all data of the rocks are distributed in adakitic region and show the evolution trend of trondhjemite. Therefore, those rocks are typical O-type adakites. Of those rocks with their intergrowths εNd （ t ） , ISr are close to that of Neo-paleozoic basalt, tDM （677 --845Ma） of a part of adakite are the same of that （tDM = 627 -998Ma） of Neo-paleozoic subducted oceanic slab. Their Sr-Nd isotopic and Zr/Hf-Nb/Ta ratios reveal the mixed feature of depleted mantle and lower crust, otherwise, a few adakite （tDM = 343 -- 453Ma） are derived from younger mantle of Paleozoic. Hereby, infer that the source rocks are the lower crust of accretionary terrane consisted of multi-source materials dominated by Neo-Proterozoic subducted oceanic slab. LaN/YbN-YbN and La/Sm-La diagram reveal that the adakitic magma was primitive magma created by source rocks partial melting via eclogite phase metamorphism, sodium rhyolite magmas were results of those primitive magma differentiation crystallization, but basalt should be created by deeply partial melting of the source rock. The petrochemical and trace elemental indicators show that those volcanoes were active in a continental marginal arc. This kind of arc and adakitic volcanic rocks appeared i

关 键 词：O型埃达克岩 中生代火山岩 大兴安岭南段 岩石成因 大陆动力学环境 成矿作用 

分 类 号：P588.14[天文地球—岩石学]