Petrogenesis of Late Carboniferous intrusions in the Linglong area of Eastern Tianshan, NW China, and tectonic implications: Geochronological, geochemical, and zircon Hf–O isotopic constraints

Abstract

The Linglong porphyry Cu deposit is located in the Dananhu–Tousuquan Arc Belt, adjacent to the large Tuwu–Yandong Cu deposits in Eastern Tianshan, northwest China. In this study, zircon U–Pb, whole rock geochemistry, and zircon Hf–O isotopic analyses were carried out on the Linglong intrusions (i.e., quartz albite porphyry and diorite porphyry). New SIMS zircon U–Pb dating and previous data indicate that the quartz albite porphyry occurred in the Late Carboniferous (318.6 ± 3.0 Ma), younger than emplacement of the diorite porphyry (338–340 Ma) and tonalite porphyry (332–335 Ma) in this area, as well large-scale copper mineralization (331–335 Ma) in Eastern Tianshan. The geochemistry of the quartz albite porphyry intrusions is consistent with calc-alkaline normal arc magmatism, characterized by high SiO2 (74.82–77.89 wt%), obvious Eu anomalies (0.42–0.52), high Y (21–25.9 ppm) and Yb (2.98–3.67 ppm) concentrations, moderate Mg# values (35–40), but relatively low Sr/Y (6.86–9.52)and low 10,000 Ga/Al values. In situ Hf–O isotopic analyses on zircons show that the quartz albite porphyry rocks have variable εHf(t) (+9.0 to + 13.9) and low δ18O values (4.72 to 5.84‰), suggesting a juvenile lower crust derived composition. However, the diorite porphyry intrusions show features of low SiO2 (57.51–61.12 wt%), minor Eu anomalies (0.82–1.15), strong depletion in high field strength elements (e.g., Nb, Ta, P and Ti), but enrichment in large ion lithophile elements (e.g., Rb, Ba, K and Pb). They also exhibit normal island arc magma geochemical signatures, with high Y (20.9–40.2 ppm), and Yb (2.75–4.64 ppm) concentrations, high Mg# (40–51), and relatively low (La/Yb)N (2.07–4.10) and Sr/Y (5.75–12.13) values, suggesting the melt was derived from the subduction-modified mantle mafic to ultramafic materials. Combined with regional tectonic evolution and our new data, we suggest that the Late Carboniferous magma was generated during the period of the northward subduction of the Paleo-Tianshan ocean plate beneath the Dananhu–Tousuquan island arc.