Conference proceeding
Quantifying magma generation mechanisms of large-volume, heterogeneous silicic eruptions in Afro-Arabian flood volcanics, Yemen
American Geophysical Union Fall Meeting, Vol.2018
American Geophysical Union 2018 fall meeting
12/2018
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 approximately 50% of the stratigraphy (Ukstins Peate et al., 2005). Whole rock compositions range from 41 to 76 wt % SiO (sub 2) 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% SiO (sub 2) ). 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 = Ab (sub 38-99) ; potassium feldspar = Or (sub 10-99) ; pyroxene = En (sub 5-92) and Wo (sub 1-48) ; 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 modeling 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.
Details
- Title: Subtitle
- Quantifying magma generation mechanisms of large-volume, heterogeneous silicic eruptions in Afro-Arabian flood volcanics, Yemen
- Creators
- Jennifer Thines - University of IowaIngrid UkstinsDavid W PeateDaniel CoulthardL. Kenneth S Horkley
- Resource Type
- Conference proceeding
- Publication Details
- American Geophysical Union Fall Meeting, Vol.2018
- Conference
- American Geophysical Union 2018 fall meeting
- Publisher
- American Geophysical Union
- Alternative title
- AGU 2018 fall meeting
- Language
- English
- Date published
- 12/2018
- Academic Unit
- Earth and Environmental Sciences; Honors Program
- Record Identifier
- 9984240780702771
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