Geochemistry and zircon U-Pb dating of Early Jurassic syenogranite in the Kaoshan area, southern part of the Zhangguangcai Range, NE China, and tectonic implications

Early Jurassic Kaoshan medium- and fine-grained syenogranites emplaced along the Yitong-Shulan Fault Zone in the southern part the Zhangguangcai Range, central Jilin Province, intruded Middle Triassic granitoids and Carboniferous-Devonian intrusive rocks. They have medium- and fine-grained textures and contain K-feldspar, quartz, plagioclase, and biotite. They are peraluminous (A/CNK = 1.13-1.20) and have high values of SiO2 (74.60-75.82 wt%), total alkalis (Na2O + K2O = 8.28-9.18 wt%), light rare earth elements (20.89-56.14 ppm), large-ion lithophile elements, and FeO/MgO = 2.78-5.93. In contrast, they feature low values of CaO (0.40-0.49 wt%), TiO2 (0.05-0.14 wt%), P2O5 (0.02-0.04 wt%), Sr (24.20-62.59 ppm), heavy rare earth elements (5.14-11.80 ppm), high-field-strength elements, and delta Eu (0.41-0.76), and the calculated zircon saturation temperatures (T-zr) range from 804 to 870 degrees C, all of which are similar to the geochemical signatures of anorogenic A(1)-type granites. Zircon U-Pb geochronology analyses from the medium- and fine-grained syenogranites yield concordia ages of 193.18 +/- 0.95 Ma (MSWD = 6.7, n = 18) and 190.29 +/- 0.92 Ma (MSWD = 8.7, n = 17), respectively, and belong to the Early Jurassic Sinemurian stage. In situ Hf isotope analyses of dated zircons yield epsilon(Hf)(t) values ranging from +17.0 to +9.7 and Hf model ages (T-DM(C)) of 225-614 Ma. Their whole-rock (Sr-87/Sr-86)(i) (0.704740-0.704133) and epsilon(Nd)(t) values (+2.8 to +0.2) are similar to those of many coeval A(2)-type granites in this region, and they form an A-type granite assemblage. Consequently, the Kaoshan medium- and fine-grained syenogranites were probably derived from partial melting of juvenile lower crust and might be related to the subduction of the Palaeo-Pacific Plate.