Genesis of the Yusupualeke Tagh granitic pluton in the South Altun and its implications for the Early Paleozoic regional tectonic evolution

This paper is the result of geological survey engineering.

Objective The Yusupualeke Tagh granitic pluton is located in the Mangya ophiolitic mélange zone, South Altun orogenic belt. It mainly comprises the medium-coarse grained porphyritic biotite monzonitic granite and medium-fine grained phenocryst-bearing biotite monzonitic granite. However, their formation ages, petrogenesis, and material sources are still controversial, which restricts the understanding of the geodynamic background for the pluton and the Early Palaeozoic tectonic evolution of the South Altun orogenic belt.

Methods To determine the formation ages, petrogenesis, and material sources of the granitic pluton, we studied petrology, zircon U-Pb chronology, whole-rock geochemistry, biotite mineral chemistry, and Hf isotopic composition of the pluton in this paper.

Results Our results show that the medium-coarse grained porphyritic biotite monzonitic granite yielded weight mean ²⁰⁶Pb/²³⁸U ages of 451-447 Ma. Combined with the formation ages (430-423 Ma) of medium-fine grained phenocrystbearing biotite monzonitic granite in our previous study, we concluded that the Yusupualeke Tagh pluton was generated at Early Paleozoic. The study of biotite mineral chemistry indicated that the studied granitoids were formed in a low-temperature/highpressure environment. Based on the mineral composition, whole rock geochemistry, and diagenetic condition, we believed that the studied granitoids should be genetically ascribed to Ⅰ-type granite. According to Hf isotopic compositions, the studied granitoids show similar Hf isotopic compositions, suggesting that they probably have similar material sources. They were mainly derived from the partial melting of the juvenile crust and mixed a small amount of ancient crust during the emplacement.

Conclusions Based on the formation age, genetic type, origin, and tectonic setting, and combined with the regional tectonic evolution, we proposed that the Yusupualeke Tagh granitic pluton was formed in an active continental margin setting related to the northward subduction of the South Altun ocean.