Crustal structure of the rifted volcanic margins and uplifted plateau of Western Yemen from receiver function analysis

Abstract

We analyse P-wave receiver functions across the western Gulf of Aden and southern Red Sea continental margins in Western Yemen to constrain crustal thickness, internal crustal structure and the bulk seismic velocity characteristics in order to address the role of magmatism, faulting and mechanical crustal thinning during continental breakup. We analyse teleseismic data from 21 stations forming the temporary Young Conjugate Margins Laboratory (YOCMAL) network together with GFZ and Yemeni permanent stations. Analysis of computed receiver functions shows that (1) the thickness of unextended crust on the Yemen plateau is ∼35 km; (2) this thins to ∼22 km in coastal areas and reaches less than 14 km on the Red Sea coast, where presence of a high-velocity lower crust is evident. The average Vp/Vs ratio for the western Yemen Plateau is 1.79, increasing to ∼1.92 near the Red Sea coast and decreasing to 1.68 for those stations located on or near the granitic rocks. Thinning of the crust, and by inference extension, occurs over a ∼130-km-wide transition zone from the Red Sea and Gulf of Aden coasts to the edges of the Yemen plateau. Thinning of continental crust is particularly localized in a <30-km-wide zone near the coastline, spatially co-incident with addition of magmatic underplate to the lower crust, above which on the surface we observe the presence of seaward dipping reflectors (SDRs) and thickened Oligo-Miocene syn-rift basaltic flows. Our results strongly suggest the presence of high-velocity mafic intrusions in the lower crust, which are likely either synrift magmatic intrusion into continental lower crust or alternatively depleted upper mantle underplated to the base of the crust during the eruption of the SDRs. Our results also point towards a regional breakup history in which the onset of rifting was synchronous along the western Gulf of Aden and southern Red Sea volcanic margins followed by a second phase of extension along the Red Sea margin.

Uppermost mantle velocity from Pn tomography in the Gulf of Aden

“…These anomalies are consistent with the teleseismic tomography fi ndings of Korostelev et al (2014) showing high-velocity anomalies of ~4% at depths of 45 km and 70 km along the western margin of Yemen. Drawing on insights from receiver functions analysis (Ahmed et al, 2013b) on October 2, 2014 geosphere.gsapubs.org Downloaded from showing spatial coincidence between regions of overthickened crust with a high Vp/Vs ratio and thick basalt fl ows (seaward dipping refl ectors) suggestive of underplated ultramafi c bodies under the crust of the Red Sea and Aden margins, we interpret our low-velocity anomalies as underplated magmatic material. We fi nd highvelocity anomalies of ~1.2%-3.7% relative to the mean mantle velocity beneath most of the plateaus and rifted margins, with the exception of locales of Holocene to recent volcanism.…”

Use of a high-precision gravity survey to understand the formation of oceanic crust and the role of melt at the southern Red Sea rift in Afar, Ethiopia

“…The intrusion of magma modifies the composition of the crust and is most commonly manifested globally at ancient rifted margins as high seismic velocities and high densities in the upper and lower crust, spatially coincident with crustal thinning across the continentocean transition (e.g. White et al 2008;Ahmed et al 2013). Despite the importance of the magma intrusion process during continental break-up, it remains unclear how molten rock is delivered into the lower crust and how it is transported through the crust to sometimes erupt at the surface.…”

Upper mantle structure of the southern Arabian margin: Insights from teleseismic tomography

“…Mechie et al (2013) imaged sharp changes in crustal thickness beneath the margins of the southern Red Sea and Gulf of Aden, probably due to the presence of highvelocity mafic bodies (Van Aven donk et al, 2009). This was confirmed by the study of Ahmed et al (2013), who imaged a transition from a 35kmthick crust (inland) to a 14kmthick crust (on the coast) across the Red Sea margin. Eastward in southern Oman the thick ness of the crust was been estimated to vary from ~35 km inland to 26 km at the coast (Tiberi et al, 2007;AlHashmi et al, 2011).…”

“…The Gulf of Aden has a magmapoor or nonvolcanic margin to the east ( Leroy et al, 2004;d'Acremont et al, 2005) and a magmarich or volcanic margin to the west (Tard et al, 1991;Leroy et al, 2012;Ahmed et al, 2013); the magmatism is commonly attributed to elevated mantle temperatures associated with a mantle plume beneath Afar. It was previously assumed that the major discontinuity of Shukra el Sheik (long ~44°E) may indicate the spatial limit of the Afar plume's influence, as it corresponds to a major change in rheology of the lithosphere (Hébert et al, 2001).…”

“…Our work incorporates data from 32 broadband stations in Yemen and 27 broadband stations in the southern Sultanate of Oman (Dhofar region: Leroy et al, 2010a;Ahmed et al, 2013;Korostelev et al, 2014;Corbeau et al, 2014) that operated during the 2009-2011 YOCMAL project (young conjugate mar gins laboratory) (Fig. 2).…”