Magmatic flux influences chemical heterogeneity of the Chaxas volcanic complex, N. Chile

Journal Article

2026

Published in: https://doi.org/10.1016/j.lithos.2026.108417

Geochemical heterogeneity vs homogeneity of ignimbrites in the Altiplano-Puna Volcanic Complex (APVC) is linked to a high vs low-flux stage of volcanism at the Chaxas Volcanic Complex. The early high-flux Pre-Chaxas stage produced the monotonous intermediate Puripicar Ignimbrite with a range in SiO2 of merely 4.4 wt % despite its large volume of ∼ 500 km3 along with several rhyolitic eruptions. Whole rock geochemistry and isotope ratios indicate the presence of both a Low and High-Sr dacite in the Puripicar reservoir. Diverse plagioclase textures and zoning from An 26 – 89 reveal a complex thermochemical history that resulted in heterogeneity within the reservoir. Amphibole atomic abundances reveal high temperature gradients and more subtle pressure gradients. Nominally high H2O contents of ∼ 6 wt % enhanced pre-eruptive homogenization of the two Puripicar dacites. The younger low-flux Chaxas Complex stage produced a dacitic dome complex and small volume rhyolitic eruptions. Plagioclase compositions of the block and ash flows are more restricted to a range of An 41 – 53 and have oscillatory textures that attest to a monotonically cooling reservoir. Isotopic ratios of the Chaxas Complex stage also indicate less prolific assimilation. Combined with previously constrained flux estimates, the geochemical characteristics of the two stages is interpreted to be a function of magmatic flux. Volcanic systems along the margins of the APVC tend to have high fluctuation in flux rates and more diverse geochemistry. This regional synthesis supports that volcanic systems marginal to continental magmatic flare-ups have systematically more geochemical heterogeneity.

• Publisher Name: Lithos
• Volume Number: 524–525