The Kengdenongshe Au–Ag–Pb–Zn polymetallic deposit, a newly discovered large-scale polymetallic deposit in the southeastern section of the East Kunlun Orogen (EKO), contains an Au resource of 40 t, Ag resource of 690 t and Pb–Zn resource of 10.5 × 105 t. The ore-bearing rocks are mainly composed of laminar barite and rhyolitic tuff. In this study, LA-ICP-MS zircon U–Pb dating and whole rock major and trace elements analyses have been conducted on the ore-bearing rhyolitic tuff. LA-ICP-MS zircon U–Pb dating data show that these rhyolitic tuffs were emplaced at ca. 243.3 ± 1.6 Ma. The samples show similar features to those of S-type granites, including high contents of SiO2 (76.4–82.6 wt. %) and Al2O3 (11.0–12.7 wt. %) and relatively low concentrations of Na2O (0.35–2.43 wt. %) and CaO (0.095–0.124 wt. %), with high A/CNK (molar [Al2O3/(CaO + Na2O + K2O)]) (1.72–2.03) and K2O/Na2O ratios (1.41–17.1). Further, they exhibit depletion in HFSEs (High Field Strength Elements) and enrichment in LREEs (Light Rare Earth Element) with negative Eu anomalies (Eu/Eu* = 0.51–0.64). These geochemical characteristics indicate that the Kengdenongcuo rhyolitic tuff originated from the fluid-absent melting of a plagioclase-poor, clay-rich metapelitic source and experienced minor fractional crystallization. In combination with arc-type magmatism and contemporaneous syn-collision granitoids in the region, the Kengdenongcuo tuff formed in a continental collision setting, implying that the Bayan Har–Songpan Ganzi Terrane collided with the East Kunlun Terrane and the Paleo-Tethys Ocean was closed at the period of ~243 Ma. The Kengdenongcuo polymetallic deposit formed at about the same time.
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.
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