Sedimentary record of the obduction of the Samail ophiolite in northern Oman: the Muti Formation in the Sail Hatat window
Résumé
The obduction of the Samail Ophiolite in Oman took place during the Upper Cretaceous. Since then, the northern
part of Oman has been relatively preserved from deformation and is therefore one of the best places to study
obduction processes. In addition, radiometric data provide good constraints on the timing of obduction from the
formation of the metamorphic sole until the exhumation of the high-pressure / low-temperature metamorphic rocks
involved in the subduction zone below the oceanic lithosphere. However, the response of the continental margin
during the obduction is still poorly constrained. If most of the models suggest the development of a flexural basin
and an associated forebulge such as in continental collision, their recognition within the syn-tectonic deposits
led to different interpretations. The geometry of the youngest syn-tectonic deposits (Fiqa Formation) is relatively
well constrained by sub-surface data that suggest a southward migration of the depocenter and progressive onlaps
on the southern margin of the basin. The context of sedimentation of the oldest syn-tectonic deposits (Muti
Formation) preserved below the nappes in the Oman Mountains is, however, still poorly understood. The location
of the sedimentation area with respect of the forebulge, for instance, remains unclear.
In order to acquire better constraints on the record, on the Arabian platform, of first steps of the obduction, the
analysis of several sections of the Muti Formation has been performed. We present here our main results for
the north-eastern part of the Oman Mountains, in the Sail Hatat window, where the thickest successions have
been described in Quryat and Bidbid area, respectively located in the eastern and western part of the Sail Hatat
window. Sedimentological and structural analysis have been combined to reconstitute the evolution of depositional
environments in areas strongly affected by deformation. In addition, systematic measurements and restoration of
palaeocurrents, petrological determinations and geochronological analyses (LA-ICPMS) on detrital zircons have
been performed in order to identify the source areas.
In both studied areas, the sedimentary series are characterised by mainly carbonated slope to basin deposits.
The more distal deposits identified are in the easternmost part (Quryat area). Episodes of terrigenous input
are recorded in both areas and palaeocurrents indicate a source area located toward the south, in agreement
with the dating obtained on detrital zircons, yielding a dominant population at ca. 800 Ma. These results
suggest that the Proterozoic basement was being eroded during the sedimentation of the Muti Formation
in the Sail Hatat window and an episode of uplift of the Huqf High is therefore inferred. These results allow
to discuss the evolution of the north-easternmost part of the Arabian platform during the first steps of the obduction.