LA-ICP-MS zircon U-Pb age and geochemical characteristics of the Taohaotuoxiquan gabbro in northern Alxa, Inner Mongolia

In Qinggeletu area of northern Alxa within Inner Mongolia, several mafic plutons are sporadically outcropped, of which the Taohaotuoxiquan gabbro is the largest one. These mafic plutons were previously considered to be Early Paleozoic in age. LA-ICP-MS zircon U-Pb dating of two samples from Taohaotuoxiquan gabbro yielded a consistent age of 276~275Ma, suggesting an emplacement of Early Permian. Geochemical characteristics of the Taohaotuoxiquan gabbro indicate that it contains some fractional crystallized plagioclase with the Nb negative anomaly inherited from its source, implying that this gabbro was formed in a subduction setting rather than in the continental rift. Combined with previous studies, the authors hold that a large amount of mantle-derived melt was involved in Late Carboniferous-Permian magmatism in northern Alxa, and this area might have been an arc in a subduction setting at that time.