Objective The composition and age of metamorphic rocks provide a crucial window into understanding the nature, formation, and evolution of orogenic belt basements. Based on an analysis of zircon age and trace elements from the Xingeer Formation in the eastern part of the South Tianshan Orogenic Belt, this paper explores the age of meta−rhyolite and its significance for the tectonic evolution of the Southern Tianshan orogenic belt.

Methods The lithology, LA−ICP−MS zircon U−Pb dating, and zircon trace element analysis of the meta−rhyolite in the Xingeer Formation, located in the eastern part of the South Tianshan Orogenic Belt, have been systematically conducted. The data have been comprehensively analyzed in conjunction with regional research findings.

Results LA−ICP−MS zircon U−Pb dating results indicate that the protolith was formed in the Early Devonian (418~412 Ma). The zircon exhibits a relative depletion in light rare earth elements (LREE) and enrichment in heavy rare earth elements (HREE), characterized by a negative Eu anomaly and a positive Ce anomaly. Trace element analysis reveals positive anomalies of U and Hf, along with negative anomalies of Nb, La, Pr, and Ti. Based on zircon trace element analysis, it is inferred that the crustal thickness at the time of rhyolite eruption was less than 35 km, with evidence of plagioclase fractionation and crystallization in the magmatic source region. The zircon Ti thermometer indicates a high magmatic crystallization temperature (>800°C), suggesting a high−temperature magmatic origin. This implies that the rhyolite's development may be associated with continental rifting.

Conclusions Based on previous studies, it is inferred that the South Tianshan Orogenic Belt may have been part of the Tarim Craton during the Early Paleozoic, with its northern margin representing an active continental margin. Influenced by subduction and retreat along the northern margin, the South Tianshan region experienced significant back−arc extension during the Late Silurian to Early Devonian. The meta−rhyolite identified in this study is likely to have formed within the tectonic setting of Early Devonian back−arc extensional rifting.