Late Jurassic Wenjiaping high Sr/Y granite: A product of partial melting of the Precambrian basement rocks trigged by lithospheric extension in the Songpan–Garzê fold belt, SW China

Abstract

The Wenjiaping granite, as one of the few Late Jurassic granites in the Songpan-Garzê fold belt (SGFB), can provide an important clue for comprehensively recognizing the tectonic evolution and mineralization of this belt. In this contribution, we present new age and geochemical data for this pluton to better constrain its petrogenesis and discuss the tectonic and metallogenic implications. LA-ICP-MS zircon U-Pb dating shows that the Wenjiaping pluton was emplaced at ~159 Ma. The granite contains minor amphibole, and exhibits slightly peraluminous characteristics (A/CNK = 1.03-1.10) and lower initial Sr-Pb isotope ratios than those of the Liwu Group, which excludes the possibility that the Wenjiaping granite was derived from partial melting of the metasedimentary rock-dominated Liwu Group as previously suggested. Significantly, high Sr/Y (40.93-54.30), La N /Yb N (39.64-56.64), and K 2 O/ NaO (0.77-1.11) ratios, low MgO (0.47%-0.86%) and Cr (25.1-41.3 ppm) contents, and relatively enriched Sr-Nd-Pb-Hf isotope compositions of the Wenjiaping granite are comparable to those of the Late Triassic adakitic rocks in the SGFB, indicating that they probably share a similar source. Combined with previous researches, we propose that large-scale detachment of the Jianglang dome caused by post-collisional lithospheric extension in the SGFB-induced decompressional partial melting of the Precambrian basement rocks can account for the generation of the Late Jurassic Wenjiaping pluton. In addition, our results also suggest that the Wenjiaping pluton probably cannot supply abundant metal elements for the Liwu-type Cu-polymetallic deposits in the Jianglang dome, SGFB.