Geochronology and geological significance of the granites from the Mahe Mo deposit in the North Qinling
北秦岭马河钼矿区花岗岩类的锆石U-Pb年龄、地球化学特征及其地质意义

LA-ICP-MS U-Pb dating for the granites from the Taoguanping and Xigou plutons in the Mahe Mo deposit in the North Qinling yields concordant ages of 157±1Ma (NSWD=13) and 153±1Ma (NSWD=14)respectively indicating that the two plutons were formed at late Jurassic. The Mahe Mo deposit is closely related to the two plutons. Therefore these ages may suggest the Mo deposit formed at Late Jurassic appreciably later than 157~153Ma. The granites from the Taoguanping and Xigou plutons are characterized by high in silica (68.12%~76.33%) and alkali (Na2O+K2O=6.35%~10.38%) with the A/CNK of 0.85~1.14 and lager variation of K2O/Na2O (0.91~1.89), showing that they are metaluminous or weakly peraluminous and high-K calc-alkaline series. The Taoguanping and Xigou granites are enriched in U, Pb, Hf, but depleted in Rb, Ba, K, Sr and P. The REE patterns are characterized by enrichment in LREE with weak negative abnormal of Eu (0.5~0.9), but a few samples have weak positive Eu anomalies (1.05 to 1.08). The granites are similar to the molybdenum deposits related granites in the southern margin of the North China Block in enriched in SiO2 and Na2O+K2O. However, these granites are lower in SiO2,Na2O+K2O and higher in CaO and MgO than the granites in the southern margin of the North China Block. It may be one reason that the Mahe Mo deposit is not as larger as the deposits in the southern margin of the North China Block.