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Yidun arc is an important constituent of the Sanjiang Tethyan Domain in SW China. The Changdagou pluton, located in the northern part of the Yidun Arc, mainly consists of granodiorite. In this study, we conducted in-situ LA-ICP-MS zircon U-Pb dating, and trace element and Hf isotope analyses on the Changdagou granites. Age dating results yielded a weighted mean U-Pb age of 214.97 &#177; 0.98 Ma (MSWD = 1.2, 2&#963;), broadly coeval with extensive late Triassic magmatism across the Yidun Arc. All zircon grains analyzed showed high concentrations of Th, U, and HREE, with positive Ce and negative Eu anomalies. Log<i>fo</i>₂ and Ce_N/Ce_N* values vary from FMQ &#8722;3.14 to FMQ +7.44 (average FMQ +3.98), and 14 to 172 (avg. 98), respectively. The zircon Eu_N/Eu_N* (avg. 0.22) ratios have no clear correlation with the Ce_N/Ce_N* ratios, suggesting that the former were mainly affected by the magma water content. In addition, zircon &#949;Hf(<i>t</i>) values vary in a narrow range (&#8722;2.9 to &#8722;4.9, avg. &#8722;3.4) that clusters around zero, indicating a greater component of mantle-derived magma. Hence, we propose that the Changdagou granodiorite was derived from a highly oxidized, &#8220;wet&#8221;, Cu-rich source, of the type likely to generate porphyry Cu mineralization. However, these parameters (log<i>fO</i>₂, Eu_N/Eu_N*, (Ce/Nd)/Y, and &#949;Hf(t)) are all lower than those of intrusions associated with Cu ores at Pulang and Lannitang, which may explain why the Cu deposit discovered at Changdagou is small by comparison. Furthermore, on the basis of the decreasing trends of &#949;Hf, log<i>fO</i>₂, and H₂O content from south to north along the Yiduan arc, we infer that the northern segment of the Yidun arc (including Changdagou) was located further away from the subduction front.