黑龙江伊春地区晚三叠世—早侏罗世铝质A型正长-碱长花岗岩地球化学特征及其构造意义  

Geochemistry of Late Triassic-Early Jurassic aluminous A-type syenogranite-alkali feldspar granite in Yichun area,Heilongjiang Province and its tectonic implications

作　　者：韩振哲[1,2,3] 赵海玲[1,2] 王盘喜[1] 杨霄[1] 牛延宏 赵寒冬[1,2,3] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]中国地质大学岩石圈构造深部过程及探测技术教育部重点实验室,北京100083 [3]黑龙江省地质调查研究总院齐齐哈尔分院,黑龙江齐齐哈尔161005

出　　处：《岩石矿物学杂志》2009年第2期97-108,共12页Acta Petrologica et Mineralogica

基　　金：中国地质调查局基础地质调查项目(200313000035);国家自然科学基金资助项目(40672088)

摘　　要：黑龙江伊春地区晚三叠世-早侏罗世正长-碱长花岗岩的岩石学和主、微量元素及同位素分析结果表明，岩石中大多含有高温自形或锥形石英、副矿物萤石和文象结构、晶洞构造等；岩石化学特征上具有高硅、富碱和低钙镁、偏铝质-过铝质特点，稀土元素配分模式呈轻稀土元素略微富集的、缓向右倾斜而重稀土元素较为平坦、铕亏损的海鸥型，富集高场强元素（HFS）Zr和Ga，亏损Ba、Sr、Eu等；岩石中的石英包裹体均一温度为750～950℃，具有高温岩浆浅成被动就位的特征。岩石富SiO2、K2O、Al2O3，δ^18O值为5．1％o～10．3％0，属正常略偏低δ^18O值花岗岩类；Isc值较高、εNd值较低，暗示了其源区物质来源主要与古老下地壳变质基底物质有关，并涉及到一定程度的壳幔岩浆混合作用。综合这些特征，首次提出伊春地区晚三叠世-早侏罗世正长-碱长花岗岩属于铝质A2型花岗岩，这说明此后该地区进入了古亚洲洋最终闭合之后大陆碰撞后跨塌、伸展动力学体制的构造背景。An analysis of petrography, major elements, trace elements and isotopic elements of Late Triassic-Early Jurassic syenogranites-alkali feldspar granites in Yichun area of Heilongjiang Province shows that most of these rocks have high temperature idiomorphic or conical quartz, accessory mineral fluorite, graphic texture and drusitic structure. Lithochemically, they are characterized by high silicon, enrichment of alkali, low calcium and magnesium and meta-aluminous to peraluminous nature. The REE distribution patterns show slight LREE enrichment with gentle right-oblique deviation and relative flat HREE pattern, sea-gull model of europium depletion, concentration of HFS elements such as Zr, Ce, Y and Ga, and depletion of Ba, Sr and Eu. Homogenization temperatures of quartz inclusions in these rocks are 750 - 950℃, indicating characteristics of high temperature hypabyssal magmatic passive injection. Syenogranites-alkali feldspar granites are rich in SiO2, K2O and Al2O3, and the values of δ^18O are 5.1‰ - 10.3‰, belonging to granitic rock of normal or somewhat lower δ^18O values. The values of Isr are relatively high and the values of of εNd are comparatively low, suggesting that original source materials of the source area are related to the metamorphic basement of the primeval lower crust, and also to a definite extent of crust-mantle magmatie mixing. Based on an integrated analysis, the authors hold that the Late Triassic-Early Jurassic syenogranites-alkali feldspar granites in Yichun area of Heilongjiang Province should belong to aluminous A2-type granites, and the tectonic background might be continental postcollisional collapse and extensional dynamic regime after the ultimate closure of the paleo-Asian ocean.

关 键 词：正长-碱长花岗岩 铝质A型花岗岩 晚三叠世-早侏罗世 造山后 伊春地区 

分 类 号：P588.121[天文地球—岩石学] P59[天文地球—地质学]