Petrogenesis Of The Lujiaying Megaporphyric Granite And Its Tectonic Implications Within Kangbao County,North Hebei Province

Lujiaying megaporphyric granite in the west of Kangbao County, whose exposure area has about 90 square kilometers. K-feldspar megaphenocrysts have a unique petrogenesis. The tectonic background of Lujiaying megaporphyric granite reveal the evolution of northern margin of North China Craton.Lujiaying megaporphyric granite consist of eastern marginal facies and western central facies. By compare of mineral composition and the use of mineral geothermobarometer inversed magmatic crystallization process. K-feldspar megaphenocrysts, large biotite and a little of plagioclase formed in the first stage. The temperature of system decreased following with the moving of magma, then magmatic crystallization process enter into the second stage. Plagioclase, K-feldspar and quartz crystallized largely. They were smaller than K-feldspar magacryst because of higher nucleation density.Dioritic enclave, fused inclusion and the wave of feldspar composition profile all indicate magma mixing. New magma bring about material and energy, which offer ideal conditions for K-feldspar megaphenocrysts' growth. At the same time, magma mixing influenced the evolution of magmatic component.Geochemical characteristics indicate it belong to peraluminous alkaline granite and have the characteristics of high fractionated A-type granite. REE distribution patterns and the composition characteristics of biotite both indicate its crustal source. Zircon U-Pb geochronology manifest the granite formed about 1244±18Ma. Diagrams for discriminating tectonic settings show this magmatism is the product of continental crust partial melting in a stretching background.