Zircon LA-ICP-MS U-Pb dating and tectonic setting of volcanic rocks from Baishan Formation in Late Carboniferous in Yagan area, Inner Mongolia

Arc igneous rocks play the key role in tracing the magmatic process in the subduction zone.The Baishan Formation in the Yagan region is mainly composed of rhyolite, dacite, rhyolitic crystal tuff and dacitic crystal tuff.LA-ICP-MS U-Pb dating were conducted on zircons from the rhyolites, and the weighted mean ages are 309±1 Ma, 308±1 Ma and 300±2 Ma, suggesting that the volcanic rocks was erupted during Late Carboniferous.The rhyolites have high SiO₂(70.98%~75.45%) and Na₂O(2.90%~5.23%) contents, and all samples are relatively rich in Na and have the average Na₂O/K₂O ratios of 1.57.The volcanic rocks are relatively enriched in large ion lithophile elements, such as Rb, K and U, and depleted in high field strength elements, such as Nb, P and Ti.They show right-leaning chondrite-normalized patterns, which means enrichment in LREE and depletion in HREE, with(La/Yb) _N ratios of 3.24~9.99, (La/Sm) _N ratios of 4.47~8.31 and significant Eu negative anomalies(average value of δEu is 0.22).The geochemical characteristics of Baishan Formation volcanic rocks are similar to arc-related magmatism.These rocks are likely formed in a continental margin arc setting, and products of the subduction of the paleo-Asian ocean during Late Carboniferous.