LA-ICP-MS zircon U-Pb dating, trace element and Hf isotope geochemistry of the Heyu granite batholith, eastern Qinling, central China: Implications for Mesozoic tectono-magmatic evolution

摘要

Mesozoic granitoids are widespread in the southern margin of the North China Craton, and of particular geological interests because of their indication for lithospheric evolution and close association with porphyry Mo mineralization. In this contribution, in situ LA-ICP-MS U-Pb, Hf isotope and trace element analyses of zircon crystals have been combined to constrain the emplacement time and petrogenesis of the Heyu granitic batholith which hosts the Yuchiling porphyry Mo system, Henan Province, China. As inferred from field investigations, the concentrically zoned Heyu batholith mainly consists of four texturally distinguishable phases, and displays a pattern of monotonically decreasing U-Pb age from 143.0±1.6 Ma for Phase 1, through 138.4± 1.5 Ma for Phase 2, through to ca. 135 Ma for Phase 3, and to 133.6 ± 1.3 Ma for the Mo-mineralized Yuchiling granite porphyry (Phase 4). The sHf(t) values ( - 27.7 to -3.4) and the two stage Hf model ages (1403 to 2924 Ma) of zircon grains, together with the ages of local strata, suggest that the magmas forming the Heyu batholith were dominantly sourced from the crust, with input of a mantle component. The higher Ce/Ce* ratios of the zircon crystals in the mineralized Yuchiling porphyry compared to those in the Mo-barren phases suggests that fluids exsolved from oxidic magmas might be more favorable for Mo enrichment. A regional synthesis suggests that intensive lithospheric thinning in the southern margin of the North China Craton should not be earlier than 130 Ma.