Petrogenesis and Tectonic Implications of Jurassic Granites in the Xingcheng Area, Northeastern North China Craton

New integrated geochemical studies are reported for Jurassic granites of the Xingcheng area in the northeastern North China Craton. U-Pb zircon data indicate that the Huashan and Taili monzogranites were emplaced during the Early (189 +/- 2 Ma) and Late (155 +/- 1 Ma) Jurassic, respectively. They are typical of high-K calc-alkaline series rocks and I-type granites, according to our whole-rock geochemical researches. Both Early and Late Jurassic monzogranites show adakitic rock characteristics because of their high Sr contents (221-347 ppm) and Sr/Y ratios (28.7-37.5), and low Y contents (7.83 -14.7 ppm). The Early Jurassic monzogranite samples have an (Sr-87/Sr-86)(i) ratio of 0.7046, SMALL ELEMENT OFNd(t) values of -11.62 to -11.51, and SMALL ELEMENT OFHf(t) values of -13.6 to -6.4, whereas the Late Jurassic monzogranites have higher (Sr-87/Sr-86)(i) ratios of 0.7069-0.7071 and lower SMALL ELEMENT OFNd(t) (-20.65 to -20.46) and SMALL ELEMENT OFHf(t) (-27.6 to -20.0) values. We suggest that the Early Jurassic adakitic rocks were derived from partial melting of thickened lower crust contaminated with mantle-derived materials, related to subduction of the Paleo-Pacific Plate. The Late Jurassic adakitic rocks were derived from partial melting of thickened lower crust in an extensional tectonic setting associated with an active continental margin.