Geochronology and Geochemistry of the Late Triassic Cu-Bearing Granodiorite Porphyry at Changdagou, Northern Yidun Arc, SW China

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Abstract
The magma sources and tectonic significance of Late Triassic Cu-bearing intrusions in the northern Yidun Arc remain less well constrained than those of the southern segment. This study integrates geological observations, zircon U–Pb geochronology and whole-rock geochemistry to investigate the Changdagou granodiorite porphyry. LA-ICP-MS analyses of 23 magmatic zircons yield a weighted mean 206Pb/238U age of 215.4 ± 0.5 Ma (MSWD = 0.53), constraining Late Triassic crystallization of the Cu-bearing intrusion. The analyzed rocks contain 67.40–68.16 wt.% SiO2 and exhibit high-K calc-alkaline and weakly peraluminous compositions, with A/CNK values of 1.03–1.14. Their rare earth element patterns show light rare earth element enrichment relative to heavy rare earth elements and negative Eu anomalies (δEu = 0.48–0.68). Primitive mantle-normalized patterns display enrichment in Rb, Th and K and depletion in Nb, Ta, P and Ti. Low Ga/Al ratios and decreasing P2O5 contents with increasing SiO2 support an I-type granitoid affinity. Relatively low Mg# values (33–36), together with low Nd/Th and Nb/Ta ratios, suggest a substantial crustal contribution to magma generation. Trace-element discrimination results and regional geological relationships support an association with the tectonomagmatic system established by westward subduction of the Ganzi–Litang Ocean. These results complement previous zircon-based investigations by providing whole-rock constraints on the petrogenesis and tectonic affinity of the Changdagou intrusion within the Late Triassic magmatic framework of the northern Yidun Arc.
Funding Information
  • National Key Research and Development Program of China (2024YFC2910102)
  • National Natural Science Foundation of China (42672128)

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