摘要
通过对吉林和龙地区勇新岩体岩石学、岩石化学、岩石地球化学及锆石U—Pb年代学等方面的研究,探讨其形成时代、岩石成因、形成构造环境等问题。勇新岩体岩石类型为二长花岗岩,与围岩新元古代长仁岩组大理岩接触带上,见有石英、钾长石与方解石共生现象;岩体中见有辉长岩脉;镜下观察,长英质矿物重结晶现象发育,并见有斜长石残斑。岩石化学、地球化学分析结果显示,二长花岗岩高硅富铝贫镁,属于过铝质、高钾钙碱性系列,成因类型为S (I)型花岗岩;δEu值0. 09～0. 77,平均值0. 47,显示为较强烈的Eu负异常,La_N/Yb_N值12. 61～25. 77,平均值22. 57,轻重稀土分馏明显;富集大离子亲石元素Rb、K和Th等活泼的不相容元素,明显亏损Nb、Ta、Zr、P、Ti等高场强元素。LA—ICP—MS锆石U—Pb定年结果表明勇新岩体形成于中三叠世,其年龄分别为236. 9±1. 1 Ma和236. 5±1. 1 Ma。结合区域资料,认为勇新岩体形成于中下地壳的原地重熔,与古亚洲洋闭合后的岩石圈伸展密切相关。
The formation age,rock genesis,and tectonic environment of the Yongxin pluton were investigated by the research on petrology,rock geochemistry and zircon U-Pb geochronology in Helong area,Jilin Province.Yongxin pluton consists of monzogranite,with symbiosis of quartz,K-feldspar and calcite in its contact belt with host rocks,which are marble of the Neoproterozoic Changrenyan Formation. Gabbro veins are found in the pluton.The felsic mineral recrystallization can be identified under microscopic observation,with residual phenocryst of plagioclase. The analysis of geochemistry indicates that the monzogranite is with high silicon and aluminum but low magnesium,which belongs to the peraluminous,high-potassic,calcium-alkaline series,type S( I) granite. The δEu values are 0. 09~0. 77,with an average of 0. 47,showing a strong negative Eu anomaly. The La_N/Yb_N values are 12. 61~25. 77,with an average of 22. 57,indicating obvious fractionation between light and heavy rare earth elements. It is enriched in large ion lithophilic elements such as Rb,K and Th( active incompatible elements),but depleted in high field strength elements such as Nb,Ta,Zr,P,and Ti. The LA-ICP-MS zircon U-Pb dating results indicate that the Yongxin pluton formed in Middle Triassic,with ages of 236. 9 ± 1. 1 Ma and 236. 5 ± 1. 1Ma respectively. Integrating the regional geological data,it is suggested that the Yongxin pluton formed from in-situ remelting of mid-lower crust,which was closely related to the extension of the lithosphere after the closure of the Paleo-Asian Ocean.
作者
闫冬
臧兴运
马春生
支宇博
王福亮
YAN Dong;ZANG Xing-yun;MA Chun-sheng;ZHI Yu-ho;WANG Fu-liang(Geological Survey of Jilin Province,Changchun 130102,China)
出处
《世界地质》
CAS
2018年第3期724-736,共13页
World Geology
基金
中国地质调查局项目(1212011220473)资助
关键词
勇新岩体
中三叠世
原地重熔
古亚洲洋
Yongxin pluton
Middle Triassic
in-situ remelting
Paleo-Asian Ocean
