兴安地块南段晚泥盆世包格德岩体时代的厘定及地质意义

The determination of Late Devonian Baogede granite in the southern part of the Xing'an block and its significance

中亚造山带东端兴安地块南段的包格德岩体由石英二长岩、二长花岗岩和花岗斑岩3种岩性组成,岩体锆石LA-ICP-MS U-Pb定年结果分别为368±1 Ma、364±1 Ma、355±1 Ma,为晚泥盆-早石炭世岩浆活动的产物;岩体的(Na_(2)O+K_(2)O)含量为7.62%~8.82%,K_(2)O/Na_(2)O值为0.93~4.21,具有富碱且相对富钾的特点,A/CNK为0.95~1.20,以准铝质-弱过铝质为主,成因上为高钾钙碱性系列的I型花岗岩;岩体具有偏低的稀土元素总量(83.60×10-6~163.40×10-6),中等的铕负异常(δEu=0.34~0.78),相对富集大离子亲石元素(Rb、Th、K)及轻稀土元素,不同程度亏损Ba、Sr、Ti及P等元素;岩体形成于活动大陆边缘弧的伸展环境,与古亚洲洋的演化有关。

Zircon U-Pb dating and geochemical characteristics of Late Devonian Baogede granite in the southern part of the Xing'an block were studied and its petrogenesis and geological significance were discussed in this paper.The rocks are composed of quartz monzonite,monzonitic granite and granite porphyry.Zircon U-Pb dating results of syenogranite and alkali-feldspar granite are 368±1 Ma,364±1 Ma and 355±1 Ma respectively.indicating that they are the products of magmatic activity in the Late Devonian to Early Carboniferous period.(Na_(2)O+K_(2)O)=7.62%~8.82%,K_(2)O/Na_(2)O=0.93~4.21,characterized by full high alkali content and high potassium.A/CNK=0.95~1.20,suggesting metaluminous to weakly peraluminous rocks.They belong to the high-K calc-alkaline series I-type granites.They are low in total REE(83.60×10-6~163.40×10-6),and the negative europium anomaly is medium(δEu=0.34~0.78).They are rich in large ion lithophile elements(Rb,Th,K)and light rare earth elements,and have suffered from different degrees of loss of Ba,Sr,P and Ti elements.The Baogede granite was formed in an extended environment of the active continental margin,and ts formation was related to the Paleo-Asian Ocean.