The Shimian ophiolite in the western Yangtze Block, SW China: Zircon SHRIMP U-Pb ages, geochemical and Hf-O isotopic characteristics, and tectonic implications

摘要: Abstract The Shimian mafic-ultramafic rocks in the western Yangtze Block is a structurally dismembered complex which intruded by Neoproterozoic granite and faulted against Suxiong Group. In this study, we divide into two suites including Late Mesoproterozoic ophiolite Early gabbros, based on differences field occurrence, age, geochemical characteristics. mainly consist of serpentinites, basalts, rodingites. Zircon U–Pb dating using sensitive high-resolution ion microprobe (SHRIMP) gabbro sample yielded an age 1066 ± 11 Ma, representing formation ophiolite. All basalt samples are tholeiitic have normal mid-ocean ridge (N-MORB)-like immobile element patterns with negative Nb Ti anomalies. low zircon δ18O (4.6–5.6 ‰) high positive eHf(t) (+10.8 to +18.3) values indicate that these were derived from depleted mantle source. These features comparable those basaltic SSZ-type gabbros at ca. 937 Ma. isotopic characteristics similar island arc basalts. Integrating previous studies data presented contribution, suggest northwestern has probably witnessed Mesoproterozoic–Early diachronous subduction.