摘要
小兴安岭西北部新开岭地区4个花岗岩岩体锆石U-Pb年龄为:大头山石英闪长岩体(187.7±1.4)Ma,大平山二云母二长花岗岩体(170.7±1.3)Ma,大平北山黑云母二长花岗斑岩(128.0±1.1)Ma以及黑云母花岗斑岩岩脉(120.6±0.6)Ma。结合前人年龄资料,该区中生代花岗质岩浆活动可分为早中侏罗世(188～164Ma)和早白垩世(128～106Ma)两个阶段,这与中国东北地区和俄罗斯远东地区早中侏罗世和早白垩世花岗岩可以对比。从早中侏罗世到早白垩世,花岗岩质岩石显示明显的演化趋势,由准铝质—弱过铝质高钾钙碱性(或者与钙碱性过渡类型)的I型花岗岩,演变到弱过铝质高钾钙碱性—钾质高分异I型花岗岩;Sr/Y值也较低,锆石的εHf(t)值略有升高。这显示由挤压增厚地壳的下部熔融形成的早期以壳源为主的花岗岩,演变为由相对伸展减薄环境下有年轻幔源加入形成的晚期高分异I型花岗岩。从花岗岩浆的演变特点分析,结合区域上构造演化,表明该时期研究区发生了由相对挤压增厚到伸展减薄的转换,这种转换的时间大致在160Ma。
Zircon U-Pb ages of four granitoids in Xinkailing region,Northwestern Xiao Hinggan Mountain,are reported in this paper.They are（187.7±1.4） Ma for the Datoushan quartz diorite,（170.7±1.3） Ma for the Dapingshan biotite monzogranites,（128.0±1.1） Ma for the East Fudiyingzi biotite monzogranite porphyry and（120.6±0.6） Ma for biotite granite porphyry dyke,respectively.Combined with previous zircon age datas,the Mesozoic granitic magmatism in this area can be divided into two stages,Early-Middle Jurassic（188-164 Ma） and Early Cretaceous（128-106 Ma）,which are comparable with NE China and Far East Russia.From Jurassic to Cretaceous,the granitoids show clear evolution characteristics,from metaluminous-weakly peraluminous,high-K calc-alkaline（or over with calc-alkaline type） I-type granitoids to weakly peraluminous,high-K calc-alkaline to shoshonitic highly differentiated I-type granitoids,Sr/Y ratios become significantly lower and zircon εHf（t） values increased slightly.These suggest that the early high Sr/Y granitoids probably melted from the lower crust of compressional and thicken crust transferred into the late highly fractionated I-type granitoids formed in a relative extensional and thinning setting and evolved by mantle-derived materials.Evolution characteristics of granitoid magmatisms,combined with the regional tectonic evolution on the periods,indcates that the crust in the region experienced a transition from compaction and thickening setting to a relative extension and thinning setting during ca.160 Ma.
出处
《吉林大学学报（地球科学版）》
EI
CAS
CSCD
北大核心
2011年第6期1881-1900,共20页
Journal of Jilin University：Earth Science Edition
基金
国家自然科学基金重点项目(90714006)
中国地质调查局项目(1212011120135
1212010611803
1212011085474
1212011085473)
