TECTONICS OF THE ARABIAN MARGIN ASSOCIATED WITH THE FORMATION AND EXHUMATION OF HIGH-PRESSURE ROCKS, SULTANATE OF OMAN

Continental crustal rocks, now structurally beneath the allochthonous Samail ophiolite, underwent blueschist to eclogite facies metamorphism prior to the emplacement of the Oman ophiolite onto the Arabian margi n. The recognition of a major low angle fault within this polydeformed and polymetamorphosed sequence of metacarbonates, metabasites, quartz ites and quartz mica schists greatly simplifies the interpretation of the structure and metamorphic zonation within the Saih Hatat window, N E Oman. Carpholite-bearing upper plate rocks consist of pre-Permian to Jurassic rocks that have been folded into large recumbent nappe struc tures which exhibit a marked increase in deformation intensity toward the boundary with the lower plate. The lower plate rocks have higher p eak pressure and temperature assemblages; they are exposed in two wind ows separated by Jabal Abu Daud. Although more intensely deformed, the lower plate rocks are recognizable as metamorphosed continental platf orm sediments. Fold axes are parallel to the regional NNE-SSW lineatio n. Sense of shear indicators yield a transport direction of south over north in the lower plate, opposite to the sense of motion inferred fo r the emplacement of the ophiolite. Lower plate eclogite-facies metaba salts are only preserved in kilometer-scale megaboudins found in the e asternmost window at As Sifah. These metamorphic assemblages along wit h their remnant east-west fabrics define the existence of a short-live d, Arabian platform-directed, nascent subduction zone. The stretching lineation elsewhere within the upper and lower plates, the Hatat Schis t (the basement), and the metamorphic sole of the ophiolite is consist ently NNE-SSW, suggesting that the exhumation of high-pressure metamor phic rocks of Saih Hatat is related to the ophiolite obduction. Exhuma tion of the high pressure rocks was accompanied by intense deformation involving regional-scale fold nappes in a convergent margin setting. The geotherm remained suppressed for a period (>30 Myr) greater than t he thermal relaxation time of the crust. The geometric and thermal con straints from Oman may be applicable to the general problem of the for mation and preservation of high-pressure, low-temperature rocks.