Asthenospheric Flow of Plume Material Beneath Arabia Inferred From S Wave Traveltime Tomography

Abstract

Widespread Cenozoic volcanism in the Arabian Peninsula has been attributed to mantle plume activity and/or lithospheric thinning due to rift‐related extension. However, there is discrepancy between geochemical and geophysical studies about which mechanism is dominant over the other for post‐12 Ma volcanism. Plume signals in some volcanic fields in the Arabian shield are not evident in isotope analyses, but low‐velocity anomalies connected to Afar are found beneath the Arabian shield in tomographic studies and interpreted as asthenospheric flow from the Afar plume. To resolve this contradiction, we investigate the upper mantle beneath the Arabian Peninsula and northeastern Africa by inverting relative S and SKS wave arrival times recorded at dense seismic networks to derive a high‐resolution S wave velocity model. Our results clearly show a narrow, elongated low‐velocity anomaly along the Makkah‐Madinah‐Nafud (MMN) volcanic line beneath the Arabian shield at 100–300 km depth which extends northward to Harrat Ithnayn and Harrat Lunayyir, but most likely not further north. The limited extent of the low‐velocity anomaly and variations in lithospheric thickness of the Arabian shield may explain why geochemical studies did not find plume signals in some harrats. Therefore, the timing and plume signals of volcanism in western Arabia may not be age progressive from Afar. We also find a possible connection between the low‐velocity anomalies beneath Harrat Lunayyir and the MMN line, suggesting that the 2007–2009 seismic swarm may be associated with northward asthenospheric flow of plume material from Afar.

Present‐Day Motion of the Arabian Plate

“…The orientation of dyke intrusions, the roughly N‐S arrangement of the major volcanic fields (Harrat Rahat, Harrat Khaybar, and Harrat Ithnayn) as well as the linear vent systems marking their central axes all suggests a stress field dominated by E‐W to ENE‐WSW directed extension on the western margin of the plate (Camp et al., 1992; Pallister et al., 2010; Trippanera et al., 2019). This present‐day state of stress appears to be governed by northward asthenospheric flow starting beneath Afar and running through the southern Red Sea toward the western margins of the plate rather than by Precambrian basement intraplate tectonic structures (Camp & Roobol, 1989; Lim et al., 2020; Pallister et al., 2010).…”

Hidden but Ubiquitous: The Pre-Rift Continental Mantle in the Red Sea Region

“…Based on the areal distribution and type of volcanism along the Arabian Shield, Camp and Robool (1992) first proposed that the enriched material fueling Arabian volcanism derives from the northward channeling of the Afar plume along a N-S lithospheric channel. This model was further supported by paired geochemical and geophysical observations (Krienitz et al, 2009;Chang and Van der Lee, 2011;Duncan and Al-Amri, 2013;Duncan et al, 2016) suggesting a radial flow of material away from Afar channeled along zones of thinned lithosphere (Lim et al, 2020). Although material derived from the Afar plume may have influenced Arabian magmatism in the southern Red Sea region (Bertrand et al, 2003), Figure 7 shows that the isotopic compositions of most western Arabia lava fields lay on trends pointing towards an enriched source different from the Afar plume (Rooney et al, 2012), with a more enriched Nd and Hf isotope content and a less radiogenic Sr. K-Ar age determinations indicate that Marthoum pipes formed during the Late Cretaceous to the Early Eocene, thus predating the impingement of the Afar plume.…”

Spatio-temporal forecasting of future volcanism at Harrat Khaybar, Saudi Arabia

“…1) (Chang and Fig. 1 Location map of Arabian harrats in western Arabia (after Coleman et al 1983;Camp and Roobol 1992) Van der Lee 2011;Konrad et al 2016;Lim et al 2020). This second and younger phase is more alkalic, producing basanite to alkali olivine-basalt and rare more evolved magmas, erupted along a N-S axis (Camp and Roobol 1992).…”