Geochemical and Zircon Hf-O Isotopic Constraints on the Origin of Wulian A-Type Granite in Shandong Peninsula, Eastern China

Early Cretaceous A-type granitic plutons are widely distributed in Shandong Peninsula, which are of great significance to understanding the regional tectonic evolution. Here we report geochemical characteristics, geochronological results, and zircon Hf-O isotope compositions of Wulian granites to reveal its origin and geological significance. Wulian granites share most characteristics of the A(2)-type granite. Zircon U-Pb LA-ICPMS analysis for Wulian A-type granites yields average age of 116.6 +/- 2.1 Ma. Zircon O isotope values range from 4.20 parts per thousand to 5.57 parts per thousand, and these values are marginally identical to or slightly lower than those of mantle zircon (5.3 parts per thousand +/- 0.3 parts per thousand). Zircon epsilon(Hf)(t) values (-26.1-23.5) indicate an enriched source. Integrated zircon Hf-O isotope compositions indicate that the source region of Wulian granites involves the components of ancient oceanic crust. Apatites from Wulian granites have the lower chlorine (0.06 wt.%-0.15 wt.%) and higher fluorine contents (2.11 wt.%-2.48 wt.%) compared with Haiyang pluton, together with their high (La/Gd)(N), (La/Yd)(N) and low (Gd/Yb)(N) ratios and high oxygen state magma reflected from zircon, signifying that slab derived component was added into the overlying mantle region through fluid/melt. The geochemical characteristics of Wulian granites could be explained by the ridge (between the Izanagi and Pacific plates) subduction model, which began to influence the tectonic evolution of the Xuhuai region and Shandong Peninsula since similar to 130 +/- 5 Ma. The following slab window between two plates plausibly explains regional extension, resulting in hot magma upwelling and the formation of the A-type granite belt. Integrating the Lower Yangtze River belt and Shandong Peninsula A-type granite proves the northward movement of the ridge between the Pacific Plate and Izanagi Plate.

Automated summary

Wulian granites in the Shandong Peninsula have characteristics of A(2)-type granite and provide insights into their origin and geological significance. The geochemical characteristics and geochronological results suggest that the formation of Wulian granites may be related to the subduction of a ridge, resulting in regional extension and the formation of an A-type granite belt.