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

Abstract

The widespread (∼48,000 km2 ) 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°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 ∼106 years, and eruption was triggered within ∼105 years after the last recharge event.