摘要
对华北北缘中段马营地区的晚三叠纪酸性侵入岩进行了锆石U-Pb定年、岩石地球化学和锆石Hf同位素分析。马营地区晚三叠纪酸性侵入岩主要包括细粒、中粒和粗粒二长花岗岩。研究表明,马营地区二长花岗岩形成于232~236.2 Ma,SiO_(2)为74.26%~76.54%,铝指数A/CNK=1.04~1.14,K_(2) O/Na_(2) O为0.76~1.44,属过铝质高钾钙碱性花岗岩。轻重稀土分馏明显,LREE/HREE=8.89~18.28,(La/Yb)N为10.35~29.33。具负至正的Eu异常,δEu为0.59~1.22。富集大离子亲石元素Rb、Ba、Th、U、K,亏损Nb、P和Ti。马营二长花岗岩的成分受分离结晶作用控制,其部分地球化学特征接近A型花岗岩,但Zr+Nb+Ce+Y为99.8~184.5×10^(6),10000 Ga/Al为2.2~2.8,TZr为724℃~814℃,为典型的非A型花岗岩。P_(2)O_(5)随着SiO_(2)的升高呈下降趋势,并且样品中SiO_(2)含量大于75%的样品,其P_(2)O_(5)为0.01%~0.04%,与高分异I型花岗岩的特征相符。微量元素特征结合前人成果显示,马营地区二长花岗岩形成于碰撞后的伸展环境,主要起源于古老地壳,可能有少量地幔物质的贡献,说明除了碰撞后的减薄过程外,深部岩浆系统的作用可能扮演着重要的角色。
Zircon U-Pb dating,petrogeochemistry and Hf isotopic were analyzed on late Triassic acid intrusive rocks in the Maying area,northern margin of North China.The late Triassic acid intrusive rocks in Maying area mainly include fine-grained,mediumgrained and coarse-grained monzogranites.The results reveal that the monzogranites in Maying area were formed in 232~236.2 Ma,with SiO_(2)content ranging from 74.26%~76.54%,aluminum index A/CNK=1.04~1.14,with K_(2) O/NaO of 0.76~1.44,which belongs to peraluminous high potassium calc-alkaline granite.The differentiation of light and heavy rare earth is obvious,with LREE/HREE ratios of 8.89~18.28 and(La/Yb)N ratios of 10.35~29.33.There are negative to positive Eu anomalies withδEu ranging from 0.59 to 1.22.The rocks are enriched in large-ion lithophile elements such as Rb,Ba,Th,U,and K,while depleted in Nb,P,and Ti.The composition of monzogranite is controlled by fractional crystallization,and some of their geochemical characteristics are close to A-type granite,but the content of Zr+Nb+Ce+Y is range of 99.8~184.5×10^(6),10000 Ga/Al is 2.2~2.8,and TZr is 724℃~814℃,which is a typical non-A-type granite.The P_(2)O_(5)content shows a decreasing trend with the SiO_(2)content increasing,and the samples with SiO_(2)content greater than 75%,the P_(2)O_(5)content ranges from 0.01%to 0.04%,which is consistent with the characteristics of highly differentiated I-type granite.The trace elements characteristics combined with previous results show that the monzogranites in Maying area were formed in the post-collision extensional environment,mainly originated from the ancient crust with a minor contribution from mantle material,indicating that except for the post-collision thinning process,the deep magmatic system also played an important role.
作者
王稀玉
陶光活
张璞
WANG Xi-yu;TAO Guang-huo;ZHANG Pu(Hebei GEO University,Shijiazhuang 050031,China;Hebei Geological Survey Institute,Shijiazhuang,Hebei 050081,China)
出处
《河北地质大学学报》
2023年第6期1-13,共13页
Journal of Hebei Geo University
关键词
华北北缘
晚三叠纪
马营二长花岗岩
northern margin of the North China craton
late Triassic
monzogranite of Maying area
