Exceptionally High Emplacement Rate of the Afar Mantle Plume Head

Abstract

We investigated a 1‐km‐thick sequence of lava flows that erupted over the Afar plume axis in order to better understand the emplacement history of the ∼30 Ma Ethiopia‐Yemen Traps. Geochemical analyses reveal high‐titanium concentrations (TiO2 3.9 ± 0.5 wt%) in basalts close to picritic compositions. Indistinguishable 40Ar/39Ar ages throughout the section define a weighted‐mean of 31.18 ± 0.28 Ma (95% confidence). This date, together with solely normal polarity magnetization directions in 68 geomagnetically independent horizons, constrain the eruption to within chron C12n, with a maximum duration of a few hundreds of kyr for the entire 1‐km‐thick section. The rate of geomagnetic secular variation used as a chronometer refines the duration to only a few tens of kyr, leading to a local extrusion rate of 4–13 km3/yr for the Afar plume head, which greatly exceeds the average rate of 0.3–1.2 km3/yr for the entire Ethiopia‐Yemen Traps.

Non-plume flood basalt volcanism before the emplacement of the Afar mantle plume head

“…In contrast, the upper part (>~2200 m) consists mainly of thick lava flows (10-100 m), forming cliffs with clear breaks along flow contacts (Ahn et al, 2021). In the Oligocene Ethiopia-Yemen Traps consisting of a large range of compositions from low-Ti to high-Ti basalts, in particular, the eruption rate of HT2 basalt in the Waja section may have been higher than that of LT basalt in the Belessa and Lima-Limo sections (Eid et al, 2021). Section names are: Lima-Limo (LL, this study), Belessa (BE), and Waja (WA).…”

“…The Oligocene Ethiopia-Yemen Traps in the Lima-Limo section erupted at ~30 Ma (Hofmann et al, 1997;Rochette et al, 1998;Coulié et al, 2003), which was before the Afro-Arabian continental breakup (Bosworth et al, 2005). Continuous lava piles that erupted at ~30 Ma have also been found in other areas of Ethiopia (e.g., Prave et al, 2016;Lhuillier and Gilder, 2019;Eid et al, 2021). After the continental breakup, the Traps split into two parts, 90% in Ethiopia and 10% in the Arabian Peninsula (Fig.…”

“…Mantle seismic tomography also suggests that the Afar plume rises from the bottom of the lower mantle (French and Romanowicz, 2015;Boyce et al, 2021). The HT2 basalts are the earliest eruptions of the Oligocene Ethiopia-Yemen Traps and are estimated to have significantly high emplacement rates (Eid et al, 2021). However, the timing and rate of the emplacement of LT lavas have not been uniquely determined, and their eruption rates remain ambiguous (Fig.…”

“…However, the timing and rate of the emplacement of LT lavas have not been uniquely determined, and their eruption rates remain ambiguous (Fig. 1b) (Ahn et al, 2021;Eid et al, 2021).…”

Constraints on the Magma Source and Rift Evolution From Geochemistry of the Stratoid Flood Basalts (Afar, Ethiopia)

“…Volcanism in EARS began around 45 Ma in central and southern Ethiopia with the emplacement of the Ethiopian flood basalts and kimberlite magmas along the margins of the Tanzanian craton. During the Oligocene the flood basalt volcanism mainly emplaced over only ∼1 Myr, at about 30 Ma, associated with the onset of rifting and the effect of a mantle plume (Ebinger et al., 1993; Eid et al., 2021; C. Hofmann et al., 1997; Kieffer et al., 2004; Marty et al., 1996; Pik et al., 1999; Steiner et al., 2022; Zumbo et al., 1995).…”