Abstract
Breakup of continents in magma-poor setting occurs primarily by faulting and plate thinning. Spatial and temporal variations in these processes can be influenced by the pre-rift basement structure as well as by early syn-rift segmentation of the rift. In order to better understand crustal deformation and influence of pre-rift architecture on breakup we use receiver functions from teleseismic recordings from Socotra which is part of the subaerial Oligo-Miocene age southern margin of the Gulf of Aden. We determine variations in crustal thickness and elastic properties, from which we interpret the degree of extension related thinning and crustal composition. Our computed receiver functions show an average crustal thickness of ~28km for central Socotra, which decreases westward along the margin to an average of ~21km. In addition, the crust thins with proximity to the continent–ocean transition to ~16km in the northwest. Assuming an initial pre-rift crustal thickness of 35km (undeformed Arabian plate), we estimate a stretching factor in the range of ~2.1–2.4 beneath Socotra. Our results show considerable differences between the crustal structure of Socotra's eastern and western sides on either side of the Hadibo transfer zone; the east displays a clear intracrustal conversion phase and thick crust when compared with the western part. The majority of measurements across Socotra show Vp/Vs ratios of between 1.70 and 1.77 and are broadly consistent with the Vp/Vs values expected from the granitic and carbonate rock type exposed at the surface. Our results strongly suggest that intrusion of mafic rock is absent or minimal, providing evidence that mechanical thinning accommodated the majority of crustal extension. From our observations we interpret that the western part of Socotra corresponds to the necking zone of a classic magma-poor continental margin, while the eastern part corresponds to the proximal domain.
Highlights
The eastern Gulf of Aden continental margins are magma-poor oblique-rifted margins (Fig. 1a) (Bellahsen et al, 2013a; Leroy et al, 2010a)
Moho depth H and Vp/Vs results from receiver functions analysis are shown on the geological map of Socotra island Fig. (6a) and (b) respectively
We organize the results into the eastern and western domains separated by the Hadibo transfer zone (HTZ), on the basis of their differing geology and in light of contrasting crustal properties found in our new study (Fig. 2)
Summary
The eastern Gulf of Aden continental margins are magma-poor oblique-rifted margins (Fig. 1a) (Bellahsen et al, 2013a; Leroy et al, 2010a). Long fracture zones generated by transform faults impose a first order control on the along-rift segmentation of the young ocean basin (Bellahsen et al, 2013b; Leroy et al, 2012). Makes it easy to interpret the extensional and sedimentary processes active during continental breakup. The structure of the margin is interpretable on upper-crustal and crustal scale cross sections (Autin et al, 2010a; d'Acremont et al, 2005, 2006, 2010; Leroy et al, 2004, 2010a, 2012; Tiberi et al, 2007)
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