The crustal structure of the north-eastern Gulf of Aden continental margin: insights from wide-angle seismic data
2011
The wide-angle seismic (WAS) and gravity data of the Encens survey allow us to determine
the 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. Its
current geometry shows first- and second-order segmentation: our study focusses on the
Ashawq–Salalah second-order segment, between Alula–Fartak and Socotra–Hadbeen fracture
zones. 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 modelling
provides indications on its geometry: oceanic-type upper-crust (4.5 km s−1) and continentaltype
lower 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 supply
along the nascent slow-spreading ridge axis. (4) A 5 km thick intermediate velocity body (7.6
to 7.8 kms−1) exists at the crust-mantle interface below the thinned margin, the OCT and the
oceanic crust. We interpret it as an underplated mafic body, or partly intruded mafic material
emplaced during a ‘post-rift’ event, according to the presence of a young volcano evidenced
by heat-flow measurement (Encens-Flux survey) and multichannel seismic reflection (Encens
survey). We propose that the non-volcanic passive margin is affected by post-rift volcanism
suggesting that post-rift melting anomalies may influence the late evolution of non-volcanic
passive margins.
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