Geochronology and geochemistry of the Daolanghuduge A-type granite in Inner Mongolia, and its geological significance
内蒙古道郎呼都格地区A型花岗岩年代学、地球化学及地质意义

The K-feldspar granite intrusion from Daolanghuduge,Inner Mongolia,is located in the Bainaimiao arc of the northern margin of the North China Craton(NCC) .The SHRIMP analyses of zircons from the intrusion yield a weighted mean 206Pb/238U age of 139.6±1.7Ma.The intrusion is characterized by high SiO2 contents(75.79%～78.07%) ,high alkali contents(K2O+Na2O=7.39%～8.29%) but low CaO contents(0.22%～0.59%) .The K-feldspar granite is marked by a "sea-gull" pattern of REE distribution with a δEu ranging from 0.03 to 0.12,showing a relatively significant negative Eu anomaly.These rocks are enriched in Ga(21.2×10-6～26.6×10-6) ,Zr(173×10-6～417 ×10-6) ,Nb(32.3×10-6～42.4×10-6) and Y(24.6×10-6～53.9×10-6) but depleted in Sr(14×10-6～44×10-6) and Ba contents(18×10-6～211×10-6) ,and exhibit remarkably negative Ba,Sr,P,Eu and Ti anomalies on the primitive mantle-normalized trace element diagram.All these characteristics resemble A-type granites which originated from the partial melting of felsic crust under high temperature and low pressure conditions and the subsequent fractional crystallization of feldspar,titanite,etc.Combined with regional tectonic evolution,we suggest that the K-feldspar granite formed in an intraplate extensional setting.The northern margin of the NCC went through a transitional tectonic regime from compression to extension during Late Mesozoic.Under this tectonic regime,the upwelling asthenosphere provided enhanced heat flux and triggered the partial melting of the overlying felsic crust and then produced the Daolanghuduge K-feldspar granite intrusion.