Petrogenesis and tectonic significance of Late Triassic Baishiya granodiorite porphyries in the Dulan area, eastern segment of the East Kunlun Orogenic Belt, China

Abstract

The timing of closing of the A'nyemaqen Ocean—the north branch of the Palaeo‐Tethys Ocean—and the subsequent continental collision remain controversial. In this study, detailed geochronological and geochemical analyses of the Baishiya granodiorite porphyries in the Dulan area [eastern segment of the East Kunlun Orogen Belt (EKOB)] were conducted. The LA–ICP–MS zircon U–Pb dating analysis revealed that the Baishiya granodiorite porphyries were emplaced during the Late Triassic (~223 Ma) and possess adakitic features, including relatively high SiO2 (67.2–69.0 wt%), Al2O3 (15.2–15.9 wt%), and Sr (416–540 ppm) contents, low Y (10.5–12.3 ppm) and Yb (1.03–1.38 ppm) contents, and high Sr/Y and La/Yb ratios. They belong to the high‐K calc‐alkaline series and show significant light rare‐earth element enrichment, minor Eu anomalies, HFSE depletion, and LILE enrichment. The porphyries record a narrow range of (87Sr/86Sr)i ratios (0.709067–0.709920) and ɛNd(t) values (−6.84 to −5.27) with two‐stage model ages (TDM2) ranging from 1,426 to 1,554 Ma. These geochemical features imply that the Baishiya granodiorite porphyries originated from the partial melting of the thickened Mesoproterozoic lower crust by mixing with minor mantle‐derived material. Late Triassic adakitic magmatism in the eastern segment of the EKOB formed in a post‐collisional extension setting due to the closing of the A'nyemaqen Ocean since Early Triassic.