Quantifying Magma Generation Mechanisms of Large-Volume, Heterogeneous Silicic Eruptions in Afro-Arabian Flood Volcanics, Yemen
Abstract
The genesis of silicic magmas has been an area of much interest but bimodal magmatism and generation of compositional gaps in rhyolitic magmas remain enigmatic. While some large-volume silicic eruptions are homogeneous in major and trace element concentrations and phenocryst assemblages (i.e., Fish Canyon Tuff, Whitney & Stormer, 1985), compositionally zoned high-silica rhyolites have been documented (i.e., Rattlesnake Tuff, Streck & Grunder, 1997) and formation mechanisms are poorly understood. The Afro-Arabian bimodal flood volcanic province (30.2 to 27.7 Ma, Yemen and Ethiopia) provides a well-constrained test-bed for modelling formation mechanisms of highly zoned large-volume silicic magmas. Eight major silicic units and four minor silicic and mafic units have been identified at twelve sample localities in Northern Yemen and Ethiopia. Silicic units locally represent 50% of the stratigraphy (Ukstins Peate et al., 2005). Whole rock compositions range from 41 to 76 wt % SiO2 with a prominent gap between 52 to 67 wt %. Two distal Indian Ocean tephras correlated to Afro-Arabian silicic ignimbrites preserve some of the largest geochemical heterogeneities observed in individual eruptions (43 to 74 wt % and 58 to 77 wt % SiO2). Detailed mineral chemistry of feldspar, pyroxene, amphibole, and Fe-Ti oxide will assess the chemical evolution of the province as well as variability recorded within individual eruptions. Mineral compositions have a complex range: plagioclase = Ab38-99; potassium feldspar = Or10-99; pyroxene = En5-92 and Wo1-48; and sodic-calcic amphibole = Mg# of 0.2 to 0.8.Several units have distinct compositional differences between the upper and lower portions. These data, along with new bulk major and trace elements will be used as constraints for the Magma Chamber Simulator (Bohrson et al., 2014), a powerful tool that allows for modelling open-system processes in silicic magmatic systems. We hope to quantify both how these silicic magmas may be generated from extreme fractional crystallization of mafic parental melts, as well as the mechanisms for producing such large compositional ranges within individual silicic eruptive units.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.T51D0191T
- Keywords:
-
- 1038 Mantle processes;
- GEOCHEMISTRYDE: 1115 Radioisotope geochronology;
- GEOCHRONOLOGYDE: 8137 Hotspots;
- large igneous provinces;
- and flood basalt volcanism;
- TECTONOPHYSICSDE: 8450 Planetary volcanism;
- VOLCANOLOGY