OPHIOLITE OBDUCTION AND PLATE MARGIN EVOLUTION: EVIDENCE FROM THE OMAN MOUNTAINS

Three windows into the Arabian margin beneath the Samail ophiolite complex provide insights into the behavior of the continental margin during ophiolite obduction. The windows progressively sample deeper levels within the Arabian margin going from the Hawasina window in the northwest to the Jabal Akhdar window and the Saih Hatat window to the southeast. The Saih Hatat window reveals the development of at least two plates within the formerly autochthonous Arabian margin successions. The lowermost exposed plate consists of a composite plate of strongly deformed Arabian platform sediments and mafic schist associated with the original opening of the Hawasina ocean basin. Locally, these rocks preserve evidence of eclogite facies metamorphism. Overlying the lower plate is an upper plate antiformal nappe whose upper limb is pinned to the undeformed Arabian margin successions to the south and whose core consists of strongly deformed Hatat Schist. The lower limb of the nappe is truncated by the fault between the upper and lower plates. Structures within both plates exhibit the north-northeast lineation associated with latest extension of the Samail ophiolite and its emplacement. The Jabal Akhdar window exposes a large anticline developed in the post Permian shelf carbonates underlain by cleaved and more tightly folded Proterozoic sediments. The Hawasina window is the largest exposure of the Hawasina nappes and parautochthonous shelf rocks that were clearly overridden by the ophiolite. The structural style in this northernmost window has more in common with the deformation observed in the Saih Hatat window and contrasts with the structural style of the frontal Hawasina nappes exposed south and west of the mountains. These relationships suggest that the Arabian margin was not the passive recipient of the obducted Samail ophiolite.