The southeastern margin of North China Craton experienced episodic growth and underwent multiple reworking in the Precambrian crust.In the late Neoarchean,a significant tectono-thermal event occurred,resulting in the addition of new continental crust.Zircon U-Pb dating and geochemical analysis were carried out on the newly discovered gneissic monzogranite in Bengbu uplift,southeastern margin of North China Craton,and its genesis and tectonic significance were discussed.The results show that the zircons of the gneissic monzogranite have obvious core-mantle structure,with oscilla-tory growth zone and high Th/U ratio,which are characteristic of magmatic zircons.The LA-ICP-MS U-Pb age of the gneissic monzogranite is(2 557±24)Ma,indicating that it was formed in the late Neoarchean.The rock has high SiO2(69.03％-70.05％),high Al2O3(14.71％-15.63％),low MgO(0.92％-1.43％),with K2O/Na2O ratio of 0.95 to 1.06 and A/CNK ratio of 1.08 to 1.12,suggesting that they belong chemically to weak peraluminous,high fractionated high-K and calc-alkaline rocks.The rock shows enrichment in large ion lithophile elements like Rb,K,and Ba,while dis-playing depletion in high field strength elements such as Nb,Zr,P,and Y.The REE content is low(∑REE=81.25 × 10-6-123.74 ×10-6),with a significant segregation between light and heavy rare earth elements,and a(La/Yb)N ratio ranging from 52.71 to 72.13,showing a positive Eu anomaly(δEu=1.36-2.40).The above characteristics indicate that it belongs to the Ⅰ-type granite formed by partial melting of the middle and lower crust.The discovery of late Neoarchean gneissic monzogranite indicates that there was a strong tectonic thermal event in the Bengbu uplift during this period,which is consistent with the crustal growth and evolution history of the North China Craton,and supports the idea that 2.5 Ga is an important stage of lithospheric growth in the southeastern North China Craton.
NETL
NSTL
万方数据
