Late Jurassic-Early Cretaceous Plutonism in the Northern Part of the Precambrian North China Craton:SHRIMP Zircon U-Pb Dating of Diorites and Granites from the Yunmengshan Geopark,Beijing

摘要

The Yunmengshan Geopark in northern Beijing is located within the Yanshan range.It contains the Yunmengshan batholith,which is dominated by two plutons:the Yunmengshan gneissic granite and the Shicheng gneissic diorite.Four samples of the Yunmengshan gneissic granite give SHRIMP zircon U-Pb ages from 145 to 141 Ma,whereas four samples of the Shicheng gneissic diorite have ages from 159 Ma to 151 Ma.Dikes that cut the Yunmengshan diorite record SHRIMP zircon UPb age of 162±2 and 156±4 Ma.The cumulative plots of zircons from the diorites show a peak age of 155 Ma,without inherited zircon cores,and the peak age of 142 Ma for granite is interpreted as the emplacement age of the Yunmengshan granitic pluton,whose igneous zircons contain inherited zircon cores.The data presented here show that there were two pulses of magmatism:early diorites,followed c13 Ma later by true granites,which incorporated material from an older continental crust.