渤海海域蓬莱9-1大型油田是国内首次发现的中生代花岗岩潜山油藏，该岩体的地球化学特征和成因研究为渤海湾盆地中生界构造环境和陆壳生长机制提供了重要的线索。应用 LA-ICP-MS 获得蓬莱9-1潜山花岗岩体锆石 U-Pb 年龄为164±2Ma，代表岩体的形成时代。ω（SiO2）范围62．22％～70．86％，ω（K2 O）范围3．29％～4．36％，ω（CaO）范围1．71％～4．10％，碱度率 AR 为2．13～3．06，含铝指数 A／CNK 介于0．89～1．07之间，表明该岩体为准铝－弱过铝范围的高钾钙碱性Ⅰ型花岗岩；REE 配分模式程较陡的右倾模式，富集轻稀土元素（LREE）、强烈亏损重稀土元素（HREE），大离子亲石元素（LILE）富集、高场强元素 HFSE 贫化，总体具有消减带地球化学特征，表明岩浆源区与消减带组分存在密切相关；δEu 略微正异常，高 Sr、Sr／Y、La／Yb 和低 Y、Yb、Mg＃特征具有增厚基性下地壳部分熔融形成埃达克岩的特征；R1-R2判别图解和（Y＋Nb）-Rb 构造图解指示其形成于碰撞后的拉张阶段。综上分析，蓬莱9-1潜山花岗岩体为碰撞造山过程地壳增厚背景下，后碰撞阶段由于地幔上隆致使具消减带组分的下地壳物质发生部分熔融所致。其形成标志着渤海湾盆地中生代陆块汇聚碰撞的强烈主碰撞阶段已经结束，并在164Ma 期间进入到由主碰撞挤压转向后碰撞伸展演化阶段，为进一步精细确定渤海湾盆地中生代陆块汇聚碰撞造山过程提供了新的依据。%The large Penglai 9-1 oilfield in the Bohai Bay Basin is the first discovered buried hydrocarbon reservoir of the Mesozoic granite.The geochemical characteristics and origin of the rocks provide important clues for the mechanism of Mesozoic tectonic environment of and continental crust growth of Bohai Bay Basin.A new age of 164 ±2 Ma was obtained for the Penglai 9-1 granitic pluton by LA-ICP-MS,and represents the formation age of the pluton consisting mainly of quartz monzodiorite,granodiorite and monzonitic granite.The study of major elements shows that the ω(SiO2 )=62.22%~70.86%,ω(K2 O)=3.29%~4.36%,ω(CaO)=1.71%~4.10%,AR=2.13~3.06,A/CNK=0.89~1.07,indicating that the pluton belongs to I-type granite of high-k calc-alkaline series.The chondrite-normalized REE patterns show a right-dipping mode, enrichment in LREE and LILE, depletion in HREE and HFSE.The geochemical characteristics of the subduction zone components (SZC)display its close relation to the source region of magma.The granite is characterized by high contents of Sr,Sr/Y and La/Yb,and low contents of Y,Yb and Mg# ,showing characteristics of adakite rock resulting from partial melting of thickening lower crust.The R1-R2 discriminant diagram and (Y+Nb)vs Rb tectonic diagram reveal that the granite was formed in the post-collisional expansion stage.In conclusion,the Penglai 9-1 granite pluton were formed by partial melting of lower crustal materials including subduction materials in the crust thickening background due to the postcollisional extension.Its formation marks that the main collision of the Mesozoic continental convergent collision in the Bohai Bay basin had ended and entered post-collisional extension stage from the compression of the main collisional stage during the period of 164 Ma,providing new evidence to further determine the Mesozoic continental collision process in the Bohai Bay basin in detail.
展开▼
