LA-ICP-MS zircon U-Pb age, geochemistry and tectonic significance of Mesozoic A-type granites in Aershan area, Inner Mongolia

Zircon U-Pb dating results by LA-ICP-MS technique and geochemical data of Aershan granitoid plutons are reported in this paper. The results of LA-ICP-MS zircon U-Pb dating are 228.5±3.0Ma for Sanguangshan medium-grained alkali feldspar granite and 141.7±2.6Ma for Nanxing'an porphyraceous alkali feldspar granite. The age of captured zircons in Nanxing'an granite is 1847±21Ma, suggesting that Precambrian basement may exist in this region. Petrochemically, the rocks are Si-rich, K-rich, Mg-low, and Ca-poor with A/CNK in the range of 1.00~1.05. These granites are enriched in HFSE and LREE, and depleted in LILE and HREE. They show typical "right- inclined seagull wing-shaped" REE patterns, suggesting A-type granites. The whole rock Sr-Nd isotopic data (εNd(t)=2.26~5.58) show that the source of the granites in Aershan area was probably the new accreted crustal material which was derived from the depleted mantle. Late Triassic Sanguangshan A2-type granite resulted from the post-orogenic lithospheric extension setting after the closure of the Paleo-Asian Ocean. Early Cretaceous Nanxing'an A1-type granite might have been formed in a thinned continental intraplate extensional environment.