A Jurassic peraluminous leucogranite from Yiwul(u|¨)shan,western Liaoning,North China craton:age,origin and tectonic significance

【摘要】：正The Gangjia granite stock is a garnet-bearing muscovite leucogranitic body emplaced in Yiwulushan in Western Liaoning Province at the eastern segment of the Yanshan orogenic belt, North China craton.The SHRIMP U-Pb zircon age is 153±5 Ma.The Gangjia granites are peraluminous with A/CNK of more than 1.14,and exhibit a tetrad effect in their REE distribution patterns,as well as non-charge-and-radius-controlled trace element behaviour.This is in contrast to the LREE-enriched patterns of the host Liishan monzogranites.These geochemical characteristics, together with low Th/U ratios in zircon,suggest that the parental magmas for the Gangjia granites have experienced extensive magmatic differentiation,including interaction between residual melt and a coexisting high-temperature aqueous fluid.Their similarε_(Nd)(t),model ages,compatible age patterns and common volcanic arc signature in source materials between the Gangjia granites and the host L(u|¨)shan monzogranites indicate their comagmatic relationship.These unusual peraluminous leucogranites,coupled with the voluminous adakitic granites hosting them,represent typical postorogenic magmatism developed under an intra-continental extensional tectonic regime.At the very end of the prolonged Jurassic magmatic evolution in Western Liaoning,extensive fractionation of most probably ferromagnesian phases and plagioclase from a calc-alkaline magma parental to the host L(u|¨)shan pluton,with overprint of the magmatic hydrothermal fluid,produced highly evolved peraluminous parental magmas for the Gangjia granites.