Petrogenesis of Silicic Ignimbrites and Banded Tephra Shards in the Afro-Arabian Flood Volcanic Province in Yemen

L. B. Falkena, D. W. Peate, and I. U. Peate
The University of Iowa: Department of Geoscience

During the Oligocene (~26-30 Ma) the Afro-Arabian Flood Volcanic Province in Yemen and Ethiopia was erupted as a compositionally bimodal province. It contained significant volumes of silicic eruptive units, and previous studies have correlated individual silicic onland units in Yemen to tephra found in Ocean Drilling Project sites approximately 2700 km SE of Yemen in the Indian Ocean. This makes the units in the Afro-Arabian Flood Volcanic Province some of the largest silicic eruptions in Earth’s history with inferred volumes >1,000 km³. This project investigates tephra shards from the offshore ODP sites along with plagioclase hosted melt inclusions from the correlated onland ignimbrite units in Yemen. Many of these shards display a banded pattern indicating magma mingling, and electron microprobe data show that an individual shard can preserve almost the full range of SiO₂ content found in the unit as a whole. Using elemental data from melt inclusions and banded shards, compositional variations will be used to model the effects of magma mixing and crystal fractionation. Investigations will also be conducted into pre-eruptive volatile compositions (S, Cl, F) preserved in melt inclusions to estimate the atmospheric loading and potential global environmental effects for individual eruptions. The sulfur data will be compared to experimental models from Scaillet & Macdonald (2006) that predict a higher sulfur content in peralkaline silicic melts (such as Yemen- Ethiopian) than metaluminous silicic melts (such as Paran-Etendeka).

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas