吉林中部旺起花岗闪长岩锆石U-Pb年代学和岩石地球化学研究

Zircon U-Pb geochronology and petrogeochemistry of Wangqi granodiorite in central Jilin Province

对吉林省中部旺起花岗闪长岩进行了LA-ICP-MS锆石U-Pb年代学和岩石地球化学研究。LA-ICP-MS锆石U-Pb定年结果显示旺起花岗闪长岩形成时代为172. 5±1. 4 Ma,即中侏罗世。在主量元素组成上,SiO_2含量为65. 03%～66. 25%,Al_3O_2含量为15. 41%～16. 29%,Na_2O含量为4. 17%～4. 29%,MgO含量为1. 85%～2. 01%,TFe2O3含量为4. 66%～5. 37%,Mg#为41～44,属于中钾钙碱性系列。在痕量元素组成上,富集轻稀土元素(LREE)和大离子亲石元素(LILE,Rb、Th、U),亏损重稀土元素(HREE)和高场强元素(HFSE,Nb、Ta、P、Ti),具有弱的Eu负异常。Sr含量为514×10^(-6)～587×10^(-6),Y含量为12. 8×10^(-6)～15. 8×10^(-6),Yb含量为1. 27×10^(-6)～1. 58×10^(-6),其地球化学特征与埃达克质岩石具有相似性,说明旺起花岗闪长岩岩浆来源于加厚下地壳的部分熔融。结合区域同时代火成岩的空间展布特征,旺起花岗闪长岩形成于古太平洋板块向欧亚大陆下俯冲形成的活动大陆边缘环境,可能受到松嫩—张广才岭地块与佳木斯地块碰撞-拼合的叠加影响。

LA-ICP-MS zircon U-Pb chronological and petrogeochemical studies of Wangqi granodiorite in central Jilin Province have been carried out. The LA-ICP-MS zircon U-Pb dating results indicate that the crystallization age of Wangqi granodiorite is 172. 5 ± 1. 4 Ma,i. e.,the Middle Jurassic. In terms of major element composition,it has SiO2= 65. 03% ~ 66. 25%,Al3 O2= 15. 41% ~ 16. 29%,Na2 O = 4. 17% ~ 4. 29%,MgO =1. 85% ~ 2. 01%,TFe2 O3= 4. 66% ~ 5. 37%,and Mg#= 41 ~ 44. It belongs to the medium-K calc-alkaline series. In terms of trace element composition,Wangqi granodiorite is characterized by enrichment in light rare earth elements( LREE) and the large ion lithophile elements( LILE,Rb,Th and U),depletion in heavy rare earth elements( HREE) and the high field strong element( HFSE,Nb,Ta,P and Ti),and weak negative Eu anomalies.It has Sr = 514 ~ 587 × 10-6,Y = 12. 8 ~ 15. 8 × 10-6,and Yb = 1. 27 ~ 1. 58 × 10-6,exhibiting an affinity to adakitic rocks. These geochemical characteristics reveal that the magma of Wangqi granodiorite was derived from the partial melting of a thickened lower continental crust. Combined with the spatial distribution of the coeval igneous rocks,it is suggested that the Wangqi granodiorite was formed in an active continental margin related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent,and the collision-collage between Songnen-Zhangguangcai Range and Jiamusi massifs.