Geology and geochronology of the Tana Basin, Ethiopia: LIP volcanism, super eruptions and Eocene–Oligocene environmental change

A.R Prave,D Mark,H Toland,T.D Raub,C.R Bates,C.H Donaldson,D.J Condon

doi:10.1016/j.epsl.2016.03.009

Abstract

New geological and geochronological data define four episodes of volcanism for the Lake Tana region in the northern Ethiopian portion of the Afro–Arabian Large Igneous Province (LIP): pre-31 Ma flood basalt that yielded a single 40Ar/39Ar age of 34.05±0.54/0.56 Ma; thick and extensive felsic ignimbrites and rhyolites (minimum volume of 2–3×103 km3) erupted between 31.108±0.020/0.041 Ma and 30.844±0.027/0.046 Ma (U–Pb CA-ID-TIMS zircon ages); mafic volcanism bracketed by 40Ar/39Ar ages of 28.90±0.12/0.14 Ma and 23.75±0.02/0.04 Ma; and localised scoraceous basalt with an 40Ar/39Ar age of 0.033±0.005/0.005 Ma. The felsic volcanism was the product of super eruptions that created a 60–80 km diameter caldera marked by km-scale caldera-collapse fault blocks and a steep-sided basin filled with a minimum of 180 m of sediment and the present-day Lake Tana. These new data enable mapping, with a finer resolution than previously possible, Afro–Arabian LIP volcanism onto the timeline of the Eocene–Oligocene transition and show that neither the mafic nor silicic volcanism coincides directly with perturbations in the geochemical records that span that transition. Our results reinforce the view that it is not the development of a LIP alone but its rate of effusion that contributes to inducing global-scale environmental change.

Highlights

IntroductionTemporal coincidence between Large Igneous Provinces (LIPs) and worldwide environmental perturbation is often considered evidence for causality
Temporal coincidence between Large Igneous Provinces (LIPs) and worldwide environmental perturbation is often considered evidence for causality (e.g. Bond &Wignall 2014; Burgess et al 2014), yet the Afro-Arabian LIP, estimated as 0.6–1.1M km[2] and 0.35–1.0 x 106 km[3] (Mohr and Zanettin 1988; Dessert et al 2003), seemingly had little influence on Cenozoic climate (Hofmann et al 1997; Rochette et al 1998; UkstinsPeate et al 2003)
We present new geological and geochronological data that provide a refined understanding of the development of that LIP and its temporal relationship to the climatic events of the Eocene-Oligocene transition

Summary

Introduction

Temporal coincidence between Large Igneous Provinces (LIPs) and worldwide environmental perturbation is often considered evidence for causality Wignall 2014; Burgess et al 2014), yet the Afro-Arabian LIP, estimated as 0.6–1.1M km[2] and 0.35–1.0 x 106 km[3] (Mohr and Zanettin 1988; Dessert et al 2003), seemingly had little influence on Cenozoic climate The Ethiopian Highlands are a volcanic massif of flood and shield volcano basalt 0.5 to 3 km thick that form spectacular trap topography (1500 to m altitudes) flanking the Main Ethiopian Rift (Fig. 1; Mohr 1983). Felsic volcanism at 30-25, 20-15 and 12-3 Ma, and Pliocene-Quaternary basalt (Hofmann et al 1997; Pik et al 1998; Rochette et al 1998; Ayalew et al 2002; Ukstins et al 2002; Coulié et al 2003; Riisager et al 2005). 5.0-9.5 wt%) olivine- to plagioclase-phyric basalt, and dacites to rhyolites including banded finely crystalline to glassy rocks, crystal ± lithic ± vitric tuffs, obsidian-rich agglomerates and coarse ignimbrites

Results: new geological data

Results: new geochronology data

Findings

Discussion

Conclusion