Constraining the Magmatic Plumbing System in a Zoned Continental Flood Basalt Province

Abstract

The geographic heterogeneities in lava composition observed in continental flood basalt provinces could provide a probe of material upwelling from the deep mantle and their length scales, but their utility is limited by uncertainties in the locus of magmatism. We examine the magma plumbing system for the Oligocene Ethiopian flood basalts. The province, which exhibits domains defined by the eruption of low‐Ti (LT) and high‐Ti (HT) lavas, requires a magmatic plumbing system that facilitates the transit of compositionally distinct magmas through the crust without mixing. Here we present a geochemical and geochronological study of a suite of 43 dikes from western Ethiopia. We find that the dikes were dominantly emplaced contemporaneously with the Oligocene flood basalt phase of activity. The composition of the dikes is overwhelmingly LT in character, typified by an overall flat rare earth element pattern (median value of La/LuCN = 2.6), and a lack of enrichment in incompatible trace elements in comparison to the HT lavas. These observations confirm the western Ethiopian dike swarm as a source for the LT flood basalts in the Ethiopian flood basalt province. We also present tentative evidence for an eastward migration in the LT dike system over time. These observations are consistent with the terminal stages of the LT magmatism being centered on the Simien shield volcano. We conclude that the apparent separation of ~400 km between the LT and HT magma plumbing systems allowed for the development of a strongly geochemically zoned continental flood basalt province.

A reappraisal of the H–κ stacking technique: implications for global crustal structure

“…10) consistently fail their respective criteria, supporting the hypothesis that the Ps arrival is low amplitude and/or not always discernible from arrivals produced by intracrustal structure. Our observations may thus imply that the lower crustal intrusion layer and flood-basalts are thickest in the centre of the Ethiopian traps, near the major Palaeogene eruptive centres and thinner (≤5 km) or non-existent at off-flood-basalt stations, consistent with petrological studies of the Ethiopian traps (Rooney et al 2016;Rooney 2017;Rooney et al 2018).…”

“…The Ethiopian Traps largely formed at 30 Ma, with 2-3 km flood-basalts erupting atop marine sediments during the development of the Red Sea rift (e.g. Hofmann et al 1997;Rooney et al 2012Rooney et al , 2018. Wide-angle seismic (Mackenzie et al 2005) and gravity surveys (Cornwell et al 2006) reveal a 8-12-km thick, lower crustal intrusion layer below the Ethiopian plateau.…”

Distributed Extension Across the Ethiopian Rift and Plateau Illuminated by Joint Inversion of Surface Waves and Scattered Body Waves

“…Some degree of thickening by igneous intrusion is also well recorded by gravity surveys (Cornwell et al., 2006), and increased Vp / Vs ratios signifying a more mafic crustal composition (Ogden et al., 2019). Xenolith data collected along the YTVL also support underplated material beneath the near‐rift EP (Abebe et al., 1998; Adhana, 2014; Rooney et al., 2017), and melt emplacement well outside the rift axis is supported by abundant basaltic dikes (Mège & Korme, 2004; Rooney et al., 2018) west of Lake Tana, where magmatism exploited zones of pre‐existing weakness.…”

“…Geologic evidence suggests that Lake Tana was previously a particular locus for extension. Pre‐existing N‐S trending sutures in this area (Johnson et al., 2004; Shackleton, 1986) are believed to have guided plume‐fed dike swarms (Mège & Korme, 2004; Rooney et al., 2018) and may remain active zones of weakness. Multi‐phase graben faulting (Chorowicz et al., 1998, and references therein), strike‐slip motion within the God Serpent dike swarm, shear structures within their margins (Korme et al., 2004), and magnetic imbrications (Callot et al., 2001; Schultz et al., 2008) all indicate that Lake Tana has experienced localized extension episodically since the Oligocene.…”

“…NW‐SE faults in the Ogaden basin and Blue Nile basin (Figure 1b), which transect the EP and NWEP, reactivated from the early to late Jurassic and interspersed lithospheric structures that may accommodate localized extension. Interrelation between Precambrian structures, active normal faulting, and magmatism outside the MER (cf., Hautot et al., 2006) is evidenced by Paleozoic‐Mesozoic and Late Miocene‐Quaternary dike swarms to the southwest and west of Lake Tana (Chorowicz et al., 1998; Mège & Korme, 2004; Rooney et al., 2018). Today, earthquake distribution is focused within the MER and Afar, often near magmatic segments, (Greenfield et al., 2019;Keir et al., 2006, 2009; Wilks et al., 2017), and along border faults separating the MER from adjacent plateaus (La Rosa et al., 2021; Lapins et al., 2020; Lavayssière et al., 2019).…”