Geochemical evolution of large-volume silicic magmas from the Afro-Arabian Large Igneous Province

Understanding the temporal and petrogenic processes by which large volumes of silicic magma are generated has been a long-standing but elusive task. The huge volumes of magma erupted in quick succession in large igneous provinces (potentially >>1000 km3 per eruptive event) raises the questions of how these magmas are generated and how long this process takes. The Afro-Arabian large igneous province, distributed between the Yemen and East African conjugate rifted margins, has seen the emplacement of an estimated 720,000 km3 of basaltic, bimodal, and silicic magmatism over three periods between 45 and 22 Ma. Volcanism during the Oligocene Traps Phase (33.9 to 27 Ma) was marked by high-flux basaltic magmatism punctuated by silicic supereruptions. Silicic volcanism in Northern Yemen, ranging in age from 30.35 to 27.85 Ma, is characterized by voluminous (commonly >1000 km3 and up to ~3100 km3) and laterally extensive (ca. 30,000 km2) deposits of ignimbrites, tuffs, and caldera collapse breccia. Previous work divided Oligocene volcanism in Northern Yemen into three phases: Main Basalts (31 to 29.7 Ma), Main Silicics (29.7 to 29.5 Ma), and Upper Bimodal (29.6 to 27.7 Ma; Ukstins Peate et al., 2005). High precision U-Pb geochronology demonstrates the Main Silicics phase, which saw the rapid emplacement of six silicic pyroclastic units totaling >8600 km3 dense rock equivalent, represents the largest known flux of silicic volcanism on Earth. Detailed mineral chemistry and geothermometry robustly demonstrate that all but one of the eight silicic supereruptions have temperatures >900ºC. New trace element and Pb-Sr-Nd-Hf isotopic data demonstrates the genetic link between Oligocene Yemen flood basalts for all but one of the main silicic units and provides evidence for generation through fractional crystallization of parental basaltic magmas and mingling between two isotopically distinct rhyolitic magmas.