Pre-Eruptive Evolution and Timescales of Silicic Volcanism in the Tarim Large Igneous Province

The widespread (similar to 48,000 km(2)) coexisting crystal-rich monotonous intermediates (trachydacites) and crystal-poor high-silica rocks (rhyolites, ignimbrites) in the Tarim Large Igneous Province (T-LIP) offer a rare opportunity to explore pre-eruptive timescales and evolutionary patterns of different silicic magmas in LIPs. We combined information from petrography, geochemistry, crystal kinetics, and diffusion chronometry of felsic rocks from nine boreholes to investigate their pre-eruptive history. The complex reverse Ti zoning patterns in quartz corresponding to temperature variations over 100 degrees C, lognormal crystal size distributions, high-Ti rims with faster growth rates, variable pressures, and Nd isotopic modeling, indicate silicic magmas in T-LIP might have witnessed a universal evolutionary pattern of periodic recharge and rejuvenation, coarsening, and cooling and crystallization in magma chambers at different crustal levels, which we term here as RRCCC model. The uniform composition and crystallinity of trachydacites might result from latent heat buffering, and their eruption was triggered by melt-induced fracturing. The chemical and thermal gradients preserved in rhyolites were generated by thermally variable magma inputs and extensive fractionation at different pressures. Co-existence of these two types of rocks was controlled by interaction between mantle plume impingement and re-melting of hydrous crust built up by early subduction. The best-fitting Ti-in-quartz diffusion curves obtained by Neural Networks indicate that magma residence time lasted for similar to 10(6) years, and eruption was triggered within similar to 10(5) years after the last recharge event. Plain Language Summary The evolutionary patterns of silicic magmas in Large Igneous Provinces remain equivocal, and the voluminous felsic volcanic rocks (covering similar to 48,000 km(2)) in the Tarim Large Igneous Province provides a window into their generation and storage mechanisms. The felsic volcanics in the Tarim Large Igneous Province are mainly represented by trachydacites and rhyolites. The trachydacites exhibit uniform compositions and crystal contents, but the rhyolites show variable compositions and crystal contents. The quartz phenocrysts in both types of rocks show a common feature of low-Ti cores and high-Ti rims. Based on evidence from mineralogy and isotopic geochemistry, a mechanism, involving magma recharge, crystal overgrowth, and cooling and crystallization, is proposed to explain the evolutionary patterns in magma chambers. The Ti-in-quartz diffusion modeling indicates that the magmas accumulated for around 1 million years in magma chambers, and the last recharge event occurred within one hundred thousand years before the final eruption.