Crustal melting above a mantle plume: Insights from the Permian Tarim Large Igneous Province, NW China

Low NbTa rhyolites from the Permian Tarim Large Igneous Province (LIP) represent the melting products of continental crust above a mantle plume. Zircon UPb dating reveals that the Kuchehe and Dawanqi rhyolites were erupted at 292.6 ± 0.5 Ma and 274 ± 2 Ma respectively. Both rhyolite groups are characterized by pronounced negative NbTa anomalies, crust-like trace element ratios and negative εNd-Hf(t) values, consistent with a crustal origin. Newly acquired data, combined with available data in the literature, clearly show that there is an increasing trend of zircon saturation temperature (TZr) from 794 to 827 °C to 886–936 °C for the early to middle stage (293–287 Ma), followed by a decreasing TZr of 803–908 °C for the late stage (287–274 Ma) of the Tarim magmatism. The temporal changes in TZr for the Tarim rhyolites are interpreted to reflect the crustal melting behavior above a mantle plume, such that fusible materials in the crust melt at an earlier stage and refractory materials melt at a later stage. The gradual decrease in TZr, towards the final stage of the Tarim rhyolitic magmatism, reflects the gradual ‘decay’ of thermal input from mantle plume to the lithosphere in the region. This thermal model is also applicable to describe the crustal melting behavior in the Chon Aike silicic LIP of Patagonia and the Snake River Plateau-Yellowstone Plateau volcanic provinces.