The crustal structure of the north-eastern Gulf of Aden continental margin: insights from wide-angle seismic data

Abstract

International audienceThe wide-angle seismic (WAS) and gravity data of the Encens survey allow us to determinethe deep crustal structure of the north-eastern Gulf of Aden non-volcanic passive margin.The Gulf of Aden is a young oceanic basin that began to open at least 17.6 Ma ago. Itscurrent geometry shows first- and second-order segmentation: our study focusses on theAshawq–Salalah second-order segment, between Alula–Fartak and Socotra–Hadbeen fracturezones. Modelling of theWAS and gravity data (three profiles across and three along the margin)gives insights into the first- and second-order structures. (1) Continental thinning is abrupt(15–20 km thinning across 50–100 km distance). It is accommodated by several tilted blocks.(2) The ocean–continent transition (OCT) is narrow (15 km wide). The velocity modellingprovides indications on its geometry: oceanic-type upper-crust (4.5 km s−1) and continentaltypelower crust (>6.5 km s−1). (3) The thickness of the oceanic crust decreases from West(10 km) to the East (5.5 km). This pattern is probably linked to a variation of magma supplyalong the nascent slow-spreading ridge axis. (4) A 5 km thick intermediate velocity body (7.6to 7.8 kms−1) exists at the crust-mantle interface below the thinned margin, the OCT and theoceanic crust. We interpret it as an underplated mafic body, or partly intruded mafic materialemplaced during a ‘post-rift’ event, according to the presence of a young volcano evidencedby heat-flow measurement (Encens-Flux survey) and multichannel seismic reflection (Encenssurvey). We propose that the non-volcanic passive margin is affected by post-rift volcanismsuggesting that post-rift melting anomalies may influence the late evolution of non-volcanicpassive margins

Deep crustal structure across a young passive margin from wide-angle and reflection seismic data (The SARDINIA Experiment) – II. Sardinia’s margin

“…9) while it crosses profile GH within Domain V. Transfer faults may thus induce an abrupt seaward thinning of the continental crust. The 3D character of the continental margin in the non-volcanic segment of the Gulf of Aden was also interpreted to be the result of segmentation of the margin [Watremez et al, 2011]. The abrupt thinning observed on profile G 2 H 2 would thus be related to a specific feature, while the more regular thinning observed along profile GH would probably be more representative of the style of thinning of the Sardinia margin.…”

Architecture of rifted continental margins and break-up evolution: insights from the South Atlantic, North Atlantic and Red Sea–Gulf of Aden conjugate margins

“…In addition, some recent studies have proposed the occurrence of exhumed mantle between the rift basin and the first oceanic crust, based on observations of outcropping rocks in the Alpine basins and the results of DSDP boreholes in Iberia and " " Newfoundland (Beslier et al 1996;Withmarsch et al 2001). This possibility has also been suggested for the Gulf of Aden eastern margin (Leroy et al 2004;d'Acremont et al 2005;Leroy et al 2010b;Watremez et al 2010;Lucazeau et al 2010). However, the evidence for a wide belt of exhumed mantle below the Neogene sediments in the Red Sea, as proposed by some authors (Voggenreiter et al 1988;Bohannon 1989;Voggenreiter & Hotzl 1989) is scanty.…”

The continent–ocean transition at the mid-northern margin of the South China Sea

“…The thicknesses of underplated material in general is typically in excess of 5-6 km (Watremez et al, 2011;Pichot et al, 2013), which corresponds to the thicknesses of the HVL reported along the northern margin of the SCS. A previous study argued that an HVL due to underplating below the lower crust, which has a lower density than mantle material, would result in buoyancy-driven uplift (Watts, 2001).…”

“…Syn-extension sediments, which can be considered a sign of the COT, have been studied in depth in the Gulf of Aden by several authors (e.g., d" Acremont et al, 2005Acremont et al, , 2006Autin et al, 2010;Leroy et al, 2010;Watremez et al, 2011). They found that the occurrence of the syn-extension sediments is contemporaneous with the deformation of the basement in the COT and does not exist on adjacent oceanic crust, i.e., deposition precedes break-up.…”