Structural control of basement denudation during rifting revealed by low-temperature (U-Th-Sm)/He thermochronology of the Socotra Island basement-Southern Gulf of Aden margin

In the Gulf of Aden, different types of fracture zones (F.Z.) have been defined and potential links with continental transfer zones have been proposed (Bellahsen et al., 2013-this volume-a). In this study, we investigate the denudation history of the south-eastern continental margin of the Gulf of Aden on the Socotra Island, in order to highlight the interplay of normal and transfer/transform tectonic structures in the course of rift evolution. Samples belong from two distinct East and West domains of the Socotra Island separated by the continental Hadibo Transfer Zone (HTZ). Tectonic denudation started during the Priabonian-Rupelian along low-angle normal faults and removed part of the overlying sedimentary formations allowing basement exhumation toward the surface (~ 1.1-1.5 km of exhumation). Forward t-T modelling of the data requires a slightly earlier date for initiation of rifting in the E-Socotra domain (~ 38 ± 2 Ma), compared to the W-Socotra domain (~ 32 ± 2 Ma), which suggests that the HTZ was already active at that time. A second major event of basement cooling and exhumation (additional ~ 0.7-1 km), starting at about ~ 20 ± 2 Ma, has only been recorded on the E-Socotra domain. This second denudation phase significantly post-dates local rifting period but appears synchronous with Ocean Continent Transition formation (OCT: 20-17.6 Ma). This late syn-OCT uplift is maximum close to the HTZ, in the wedge of footwall delimited by this transfer system and the steep north-dipping normal faults that accommodated the vertical motion. This particular pattern of uplift and denudation during the OCT reorganisation suggests that the late uplift of the margin can be strongly differential from a segment to another, depending on the amplitude of thinning experienced by each of the adjoining segments.