Insights Into Deep Mantle Thermochemical Contributions to African Magmatism From Converted Seismic Phases

Abstract

Introduction 1.1. Background The African plate hosts numerous loci of Cenozoic magmatism (Figure 1). In East Africa, uplifted plateaus (e.g.

Body‐Wave Tomographic Imaging of the Turkana Depression: Implications for Rift Development and Plume‐Lithosphere Interactions

“…Temperature impacts and similarly, however, our S ‐wave model depicts more concentrated low wavespeeds at mantle‐transition‐zone‐depths than the P ‐wave model (Figures 7 and 8; 500–600 km; A–A’). This discrepancy could be the result of compositional heterogeneity or a hydrated mantle transition zone (e.g., Cornwell et al., 2011; Meier et al., 2009; Thompson et al., 2015), consistent with the near ubiquitous view that the African Superplume is compositionally, not just thermally anomalous (Boyce & Cottar, 2021; Ni et al., 2002; Simmons & Grand, 2002; Simmons et al., 2007).…”

“…(2021) find evidence for two separate whole‐mantle plumes: a near‐vertical plume beneath the Afar triple junction as well as the African Superplume. The morphology of the latter, as determined from gravity data (Simmons et al., 2007) and seismic waveform modeling (e.g., Ni et al., 2002), is characterized best as a sharp‐sided thermochemical plume, whereas the plume below Afar is likely a purely thermal upwelling (e.g., Boyce & Cottar, 2021).…”

“…Beneath the East African Plateau, tomography studies reveal a slow wavespeed anomaly in the upper mantle, interpreted as ascending plume material (e.g., Mulibo & Nyblade, 2013; Weeraratne et al., 2003). Tomography, in conjunction with receiver function studies of the mantle transition zone (e.g., Benoit, Nyblade, Owens, & Stuart, 2006; Boyce & Cottar, 2021; Nyblade et al., 2000; Thompson et al., 2015) that observe near‐normal mantle transition zone thicknesses below the MER but thinned in southern Ethiopia, suggest the plume is likely to cross the mantle transition zone below the Turkana Depression, which has been a large data gap prior to this study.…”

Improving Constraints on Planetary Interiors With PPs Receiver Functions

“…As a part of the prelanding studies of the InSight mission to Mars, Knapmeyer-Endrun et al (2018) have used synthetic seismograms generated by hypothetical marsquake events using different Mars prelanding models to show the potential availability of RFs can be extended by incorporating waveforms of free-surface multiples of the P-wave (PPs). Several mantle transition zone studies have incorporated PPs-RFs in their common conversion point stacking analysis on Earth (Boyce & Cottaar, 2021;Nyblade et al, 2000;Owens et al, 2000;Shen et al, 1998) while fewer studies use them to constrain the overlying crustal structure (e.g., Jones & Phinney, 1998). The infrequent use of PPs arrivals in RF analysis for crustal studies on Earth is due to the following: (a) the signal-to-noise ratio (SNR) of the PPs are typically much smaller than both Ps and Sp phases, (b) signal-generated noise that arrives within the P-coda (e.g., pP) for a shallow event can possibly contaminate the data prior to deconvolution, (c) additional constraints obtained in comparison with solely using Ps-RFs are relatively small due to small differences in ray parameters for distant earthquakes, but perhaps more fundamentally, and (d) earthquakes that are large enough for Ps RF analysis occur with sufficient frequency on Earth to reduce the need for additional data.…”

A Complex Mantle Plume Head Below East Africa‐Arabia Shaped by the Lithosphere‐Asthenosphere Boundary Topography

“…The elevated temperatures in the MTZ indicated by the low velocities where the three plumes (AP, KP, and LP) rise through it are confirmed by independent evidence from several receiver‐function studies. Differential arrival times of the P‐to‐S conversions at the 660‐ and 410‐km discontinuities indicate anomalously thin—and, thus, anomalously hot (e.g., Lebedev et al., 2003)—MTZ below Iraq, Afar, and Kenya (Boyce & Cottaar, 2021; Kaviani et al., 2018; Mulibo & Nyblade, 2013; Sun et al., 2017; Thompson et al., 2015) (Figure 6).…”