北淮阳东端牛王寨岩体年代学及地球化学研究:对大别造山带早白垩世深部地质过程的制约

Geochronology and geochemistry of Niuwangzhai pluton in east end of North Huaiyang:constraints on deep geological process of Dabie Orogen in Early Cretaceous

牛王寨岩体位于大别造山带北部北淮阳构造带东端,岩性主要为花岗岩。LA-ICP MS锆石U-Pb测年结果显示,牛王寨花岗岩形成于(119.4±1.5)Ma,属于大别造山带早白垩世晚阶段岩浆活动的产物。牛王寨花岗岩具有高硅(SiO_(2)含量为71.98%~77.96%)、高碱(全碱含量为7.66%~9.30%)、低钙(CaO含量为0.19%~0.68%)、高FeO_(T)/MgO值(平均值为12.83)和10000×Ga/Al值(2.63~2.82)的特点。岩石富集高场强元素,(Zr+Nb+Ce+Y)平均含量为294×10^(-6),富Rb、贫Ba和Sr,具有显著的Eu负异常,指示牛王寨花岗岩具有A型花岗的特点。牛王寨花岗岩^(87)Sr/^(86)Sr初始值为0.70828~0.70841,ε_(Nd)(t)值为-18.77~-19.15,判断其源区物质可能为大别山中下地壳片麻岩。约130 Ma时,大别造山带加厚下地壳拆沉引发的软流圈上涌,为源区的部分熔融提供了热源。牛王寨岩体的形成受控于约130 Ma之后中国东部统一的伸展构造事件。

Niuwangzhai granite is located in the east end of North Huaiyang in Dabie Orogen.LA-ICP MS zircon U-Pb dating indicates that the Niuwangzhai granite was emplaced at(119.4±1.5)Ma and belongs to the late-stage Early Cretaceous magmatism of Dabie Orogen.The granites are characterized with high SiO_(2)(71.98%~77.96%)and high alkali(7.66%~9.30%)contents,low CaO contents(0.19%~0.68%),and high FeO_(T)/MgO(4.04~39.04,mean value of 12.83)and 10000×Ga/Al ratios(2.63~2.82).The granites are also enriched in high field strength elements(average content of Zr+Nb+Ce+Y is 294×10^(-6))and Rb,but are depleted in Ba and Sr with apparent lowδEu values.Geochemical features suggest that the Niuwangzhai granites can be classified into A-type granites.Combined with Sr-Nd isotopic compositions,the granites were probably derived from the gneiss in middle-lower crust of Dabie Orogen.The upwelling of asthenosphere caused by 130 Ma thickened lower crust delamination probably provided heat to melt the intermediate-acid gneiss.The formation of Niuwangzhai granite was possibly associated with extensional tectonic event of eastern China in post 130 Ma.