Identification and petrogenesis of Wuhema highly fractionated I-type granitoids in Qinghai Province from Songpan-Ganzi Terrane

In order to study the genetic type and petrogenesis of the Wuhema granitoids in the Songpan Ganzi Terrane, the petrography, geochemistry, zircon U−Pb chronology and Lu-Hf isotope have been studied in this paper. The Wuhema granitic rocks are identified as highly fractionated I-type granitoids with crystallization age of 216.6±4.3 Ma. The rocks are syenogranite, and have the characteristics of weakly peraluminous, high-K calc-alkaline. The fractionation of REE in the rocks is not obvious (La/Yb)_N <7), light rare earth elements are slightly enriched, and heavy rare earth elements are gently distributed. The rocks have obvious negative Eu anomalies (δEu= 0.08 ~ 0.43), with obvious depletion of Ba, Sr and high field strength elements (HFSEs, e.g., Nb, Ta, P and Ti), and enrichment of large ion lithophile elements (LILEs, e.g., Rb, Th and U), ε_Hf(t) values of the rocks range from -2.54 to 1.32. The primary magma of the Wuhema granitic rocks were formed by the upwelling of asthenosphere caused by the lithosphere delamination, and induced the partial melting of Mesoproterozoic crustal materials (similar to metagreywacke), then the magma went through a high degree of fractionation of plagioclase, potassium feldspar, apatite and other minerals.