辽西北票早侏罗世兴隆沟组英安岩的地球化学特征  

Geochemical characteristics of the early Jurassic dacites of the Xinglonggou Formation in Beipiao area,west Liaoning province.

作　　者：李伍平[1] 

机构地区：[1]广州大学土木工程学院

出　　处：《岩石学报》2006年第6期1608-1616,共9页Acta Petrologica Sinica

基　　金：国家自然科学基金项目重点项目(批号40334039和批号40132020)联合资助

摘　　要：辽西北票早侏罗世兴隆沟组英安岩具有埃达克岩的地球化学特征。它们具有较高的SiO_2(≥63．93%)、Al_2O_3 (≥15．40%)、Na_2O(≥3．65%)和MgO(≥2．32%,Mg~#=0．48～0．61)含量,较高的Sr(＞463μg/g)、Cr(＞119μg/g)、Ni(＞75μg/g)含量,较低的Yb(＜1．70μg/g)、Y(＜17μg/g,)含量,高的La/Yb(＞18)、Sr/Y(＞34)值和低Rb/Sr(≤0．31)比值,稀土元素强烈分馏,弱的负铕异常(Eu/Eu^(?)=0．80～0．87)．它们的Nd同位素(^(143)Nd/^(144)Nd=0．512414～0．512502,ε_(ND)(t)=-2．10～-0．38,T_(DM)=0．89～1．02Ga),Sr同位素(^(87)Sr/^(86)Sr=0．7073～0．7075,εSr(t)=11．16～13．78)和Pb同位素(^(206)Pb/^(204)Pb=18．28～18．40,^(207)Pb/^(204)Pb=15．42～15．53,^(208)Pb/^(204)Pb=38．08～38．27)组成与华北陆块古老的岩石圈地幔及其中的中晚侏罗世和早白垩世火山岩不同。这表明兴隆沟组英安岩可能是古亚洲洋壳残片部分熔融形成的,熔体在上升过程中与地幔楔发生过强烈的混染作用。据此,推测古亚洲洋曾向华北陆块发生过俯冲作用。The early Jurassic dacites of the Xinglonggou Formation in Beipiao area of West Liaoning Province have similar geochemical characteristics of adakite, which is generated from partial melting of young oceanic crust. Dacites are high SiO2 （ ≥63.93% ） high Al2O3 （〉115. 40% ）high Na2O （〉13.65%） high MgO（ 〉12. 32%, 0. 48 - 0. 61 in Mg^#） lavas characterizes by high trace element contents （Cr 〉 119ppm, Ni 〉75ppm, Sr 〉463ppm）and low heavry rare earth element contents （ Yb 〈 1.70ppm, Y 〈 17ppm）, and high La/Yb （ 〉18）high Sr/Y（ 〉 34） low Rb/Sr （≤0.31） ratios, and by strongly fractianated LREE and negligible negative Eu anomalies （ Eu/Eu^＋ = 0. 80-0. 87）. Their Nd-Sr-Pb isotopic compositions （ ^143 Nd/144 Nd = 0. 512414 -0. 512502,εNd（t） = - 2. 10 - 0. 38, TDM =0. 89- 1.02Ga,^87Sr/^86Sr=0.7073-0.7075 ,εSr（t） = 11.16-13. 78 ,^206Pb/^204Pb = 18.28-18.40,^207Pb/^204Pb = 15.42-15.53, ^208Pb/^204Pb = 38.08-38.27）differ from the Archeozoic lithosphere mantle and the middle Jurassic, later Jurassic and the early Cretaceous volcanic rocks of the North China Craton. The Author thinks that the magmas were generated from partial melting of subducted oceanic slab of the Paleo-Asian Ocean and interacted with the Archeozoic lithosphere mantle during the ascending magmas, implying that the subduction of the Paleo-Asian Ocean beneath the North China Craton in Paleozoic might took placed.

关 键 词：英安岩 古亚洲洋 早侏罗世 辽西 燕山造山带 

分 类 号：P588.143[天文地球—岩石学] P534.52[天文地球—地质学]