The age and origin of the Jinfosi biotite granite, North Qilian, NW China: evidence from U-Pb zircon age data, geochemistry, and Nd-Sr-Pb isotopes

摘要

New geochemistry, Nd-Sr-Pb isotopes and U-Pb zircon data from the Jinfosi Biotite granite provide important constraints on the evolution of the crust in this part of the North Qilian, NW China. The Jinfosi Biotite granite have the following properties: SiO_2 > 65%, A/CNK(Molar Al_2O_3/(CaO + Na_2O + K_2O) ratios generally > 1.1, Na_2O generally < 3.2%, Sm/Nd values between 0.17 and 0.27, and high Rb/Sr values. A chondrite-normalized rare earth element (REE) pattern shows negative Eu anomalies and depletion in heavy REEs. ~(143)Nd/~(144)Nd values are relatively low, and values of εNd(t) and εSr(t) are indicative of continental lithosphere. (~(87)Sr/~(86)Sr)i values are between 0.69952 and 0.70962, corresponding to continental crust mixed with a minor component of mantle material. Values of ~(206)Pb/~(204)Pb, ~(207)Pb/~(204)Pb, and ~(208)Pb/~(204)Pb are 18.9-19.0, 15.59-15.85, and 38.00-and 39.00, respectively, corresponding to S-type collision-related granites. The Jinfosi Biotite granite yield a SHRIMP zircon U-Pb age of 416.7 ± 4.1 Ma. R1-R2 and Rb versus (Yb + Nb) discrimination diagrams indicate that the Jinfosi biotite granite was produced during continental collision following closure of the paleo-North Qilian Ocean.