Tectonics of the Arabian margin associated with the formation and exhumation of high‐pressure rocks, Sultanate of Oman

Abstract

Abstract. 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 margin. The recognition of a major low angle fault within this polydeformed and polymetamorphosed sequence of metacarbonates, metabasites, quartzites and quartz mica schists greatly simplifies the interpretation of the structure and metamorphic zonation within the Saih Hatat window, NE Oman. Carpholite-bearing upper plate rocks consist of pre-Permian to Jurassic rocks that have been folded into large recumbent nappe structures which exhibit a marked increase in deformation intensity toward the boundary with the lower plate. The lower plate rocks have higher peak pressure and temperature assemblages; they are exposed in two windows separated by Jabal Abu Daud. Although more intensely deformed, the lower plate rocks are recognizable as metamorphosed continental platform sediments. Fold axes are parallel to the regional NNE-SSW lineation. Sense of shear indicators yield a transport direction of south over north in the lower plate, opposite to the sense of motion inferred for the emplacement of the ophiolite. Lower plate eclogite-facies metabasalts are only preserved in kilometer-scale megaboudins found in the easternmost window at As Sifah. These metamorphic assemblages along with their remnant eastwest fabrics define the existence of a short-lived, Arabian platform-directed, nascent subduction zone. The stretching lineafion elsewhere within the upper and lower plates, the Hatat Schist (the basement), and the metamorphic sole of the ophiolite is consistently NNE-SSW, suggesting that the exhumation of high-pressure metamorphic rocks of Saih Hatat is related to the ophiolite obducfion. Exhumation 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 the thermal relaxation time of the crust. The geometric and thermal constraints from Oman may be applicable to the general problem of the formation and preservation of high-pressure, lowtemperature rocks.

Birth, death, and resurrection: The life cycle of suprasubduction zone ophiolites

“…[64] The final stage of ophiolite emplacement in Oman is well documented and will not be discussed here in detail [Bechennec et al, 1988;Cawood, 1991;Gealey, 1977;Gregory et al, 1998;Miller et al, 1998;Searle and Cox, 1999]. It is noted, however, that rapid emergence of the Semail ophiolite after subduction of the Arabian continental margin is consistent with detachment of the oceanic portion of the passive plate margin (Figure 7g).…”

Along‐axis magmatic system in the northern Oman ophiolite: Implications of compositional variation of the sheeted dike complex

“…After that, many authors insisted on supra-subduction zone environment for the genesis of the Oman ophiolite [e.g., Lachize et al, 1996;Schiano et al, 1997;Searle and Cox, 1999;Shervais, 2001]. Whereas other many authors insisted that the ophiolite was produced at fast spreading ridges without subduction [e.g., Boudier et al, 1988;Juteau et al, 1988;Ernewein et al, 1988;Nicolas et al, 1988;Rochette et al, 1991;Gregory et al, 1998]. However, the original basis of the arguments for the supra-subduction zone origin, high LILE contents, has not been reexamined.…”

“…Langmuir et al [1992] showed that MORBs from different oceans have unique features, respectively (Figure 17). [Moores et al, 2000], second is that the contamination by subduction components at suprasubduction suites as claimed by Alabaster et al [1982], and third is the contamination from subduction zone which subducted opposite side of ocean ridges as present-day southern Chile Ridge [Sturm et al, 2000], because subduction beneath Arabian Platform was claimed by Gregory et al [1998]. To solve these problems, more precise and extensive works are needed.…”

The March 11, 2002 Masafi, United Arab Emirates earthquake: Insights into the seismotectonics of the northern Oman Mountains

“…For this reason the geological studies of the Emirates and Oman have focused on the petrological details of the ocean crust (Lippard et al 1986), and the structure and stratigraphy of the rocks below the Semail (Robertson et al 1990, Searle & Cox 1999 which record the stages of the obduction process. On the basis of these data sophisticated models for oceanic crust generation, intra-oceanic crustal detachment, partial subduction of continental crust and obduction of oceanic crust have been constructed for this region (Boudier et al 1988, Hacker et al 1996, Gnos & Nicolas 1996, Gregory et al 1998.…”