Geochemistry, zircon U-Pb dating and Hf isotopies composition of Paleozoic granitoids in Jinchuan, NW China: Constraints on their petrogenesis, source characteristics and tectonic implication

摘要

Granitoids are widely distributed in Jinchuan at the southwestern margin of the North China plate, which is also an important area of mineral deposits. The research subject of this article are two Paleozoic granitoids, a cataclastic syenogranite and a granodiorite porphyry. This study presents whole rock geochemistry and zircon U-Pb-Hf isotope data for the two granitoids to determine their petrogenesis, source characteristics and tectonic significance. The cataclastic syenogranite is characterized by metaluminous composition with high potassium, and La-N/Yb-N from 39 to 48. The composition with strong negative Eu anomalies and Zircon saturation temperatures (T-Zr) from 947 to 1072 degrees C classify this intrusion as an A-type granite. The granodiorite porphyry is metaluminous with high sodium, sub-alkaline, La-N/Yb-N ratios from 27 to 32. These I-type intrusions have no Eu anomalies and T-Zr ranges from 818 to 845 degrees C. Both the cataclastic syenogranite and granodiorite porphyry show enrichment of LREE and LILE and depletion of HREE and HFSE, except Hf and Zr. Using single zircon LA-ICP-MS U-Pb dating, the emplacement age of the cataclastic syenogranite and granodiorite porphyry are determined at 433.4 +/- 3.7 Ma and 361.7 +/- 4.6 Ma, respectively. Zircons from the cataclastic syenogranits have uniform negative epsilon(Hf)(t) values (-11 +/- 0.5 to -9 +/- 0.5), implying the involvement of an old Palaeoproterozoic crustal source in magma genesis. The zircons from the granodiorite porphyry have epsilon(Hf)(t) values that range from -8 +/- 1.0 to +10 +/- 0.6, suggesting heterogeneous source materials involving both juvenile and ancient crust reworked crustal components. Based on the geological significance of granites at the southwestern margin of the North China plate, the closure of the North Qilian Ocean occurred at similar to 444 Ma. Geochemical' features suggest that the cataclastic syenogranite and granodiorite porphyry formed in an intraplate extensional and compressional setting, respectively. Hence after a period of extensional post-collisional intraplate evolution, strong compressive forces affected the area. (C) 2016 Elsevier Ltd. All rights reserved.