内蒙古赤峰金厂沟梁地区花岗岩类年代学、地球化学与Hf同位素特征

Geochronology, Geochemistry and Hf Isotopic Compositions of Granitoids in Jinchanggouliang Area, Chifeng, Inner Mongolia

内蒙古赤峰金厂沟梁地区出露的中生代花岗岩类对确定华北克拉通北缘中段中生代构造格局和演化具有重要意义.对西台子岩体、金厂沟梁岩体、小西沟岩体及西对面沟岩体进行了锆石U-Pb(LA-ICP-MS)年龄测定、地球化学分析及Hf同位素测定.西台子岩体及金厂沟梁岩体锆石U-Pb测年结果分别为220.5±2.1 Ma和225.5±1.7 Ma,为晚三叠世,两个岩体具有右倾的球粒陨石标准化配分曲线,均为弱的正Eu异常,锆石εHf(t)的变化范围分别为-8.0^-3.0和-5.7^-2.3;小西沟岩体的锆石U-Pb测年结果为162.5±1.6 Ma,为晚侏罗世,(La/Yb)N比值为0.14~0.51,其稀土元素球粒陨石标准化图谱显示稍向左倾的“V”字型,弱的负Eu异常,锆石εHf(t)为-7.3^-4.4;西对面沟岩体锆石U-Pb测年结果为128.2±1.1 Ma,为晚白垩世,具有右倾的球粒陨石标准化配分曲线,弱的正Eu异常,锆石εHf(t)为-11.4^-10.4.西台子及金厂沟梁岩体为I型花岗岩,小西沟岩体为A1型花岗岩,西对面沟岩体为C型埃达克质岩石,其源区均为华北克拉通下地壳物质的部分熔融;西台子岩体、金厂沟梁岩体可能形成于古亚洲洋闭合后地壳伸展的动力学背景之下,小西沟岩体形成于蒙古-鄂霍茨克海闭合后的伸展构造背景,西对面沟岩体形成于地壳减薄过程中局部加厚的构造背景之下.

The Mesozoic granitoids exposed in Jinchanggouliang area of Chifeng are of great significance to the Mesozoic tectonic framework and evolution in the middle part of the north margin of North China.In this study,geochemical analysis,zircon U-Pb(LA-ICP-MS)dating and Hf isotopic compositions were carried out for the Xitaizi,Jinchanggouliang,Xiaoxigou and Xiduimiangou rock bodies.U-Pb dating of zircons from Xitaizi and Jinchanggouliang rock bodies are 220.5±2.1 Ma,225.5±1.7 Ma,respectively,which are Late Triassic.The two rock bodies have similar right-leaning chondrite-normalized distribution curves and show a certain weak positive Eu anomaly.TheεHf(t)values of the two rock bodies range from-8.0 to-3.0,and-5.7 to-2.3.U-Pb dating of zircons from Xiaoxigou rock body is 162.5±1.6 Ma,which is Late Jurassic.The(La/Yb)N ratios of the rock body are 0.14 to 0.51 and have a slightly left-leaning“V”shape chondrite-normalized distribution curve and a weak negative Eu anomaly.TheεHf(t)value is-7.3 to-4.4.U-Pb dating of zircons from Xiduimiangou rock body is 128.2±1.1 Ma and has right-leaning chondrite-normalized distribution curve and shows a certain weak positive Eu anomaly.TheεHf(t)value is-11.4 to-10.4.Analyses of the above chronology,rock geochemistry and Hf isotope data,combined with regional geological data,show that Xitaizi and Jinchanggouliang rock bodies are I-type granites,Xiaoxigou rock body is A1-type granite and Xiduimiangou rock body is C-type adakite rocks.The source regions are all from the partial melting of the lower crustal materials in the North China craton.Xitaizi rock body and Jinchanggouliang rock body may have formed under the extensional dynamic background of the ancient Asian Ocean closure.Xiaoxigou rock body was formed in the extensional tectonic background after the closure of the Mongol-Okhotsk Ocean.The Xiduimiangou rock body was formed under the tectonic background of local thickening in the process of crust thinning.