Geochemistry of metamorphosed mafic rocks from Saih Hatat: pre-obduction history of NE Oman

Abstract

Field and petrological data, combined with major, trace and rare earth element analysis of mafic rocks that structurally underlie the Semail ophiolite in Saih Hatat, have led to their subdivision into five groups: (a) crossite-bearing mafic schists that represent metamorphosed within-plate alkali basalts, erupted in a Proterozoic continental rift or ocean basin setting; (b) greenschists, blueschists, garnet-blueschists, clinopyroxene-rich layers and eclogites, representing metamorphosed Permian basaltic flows and tuffs with enriched-MORB affinities; (c) crossite-bearing metavolcanics, representing alkali basalts, trachyandesites and dacites erupted on oceanic islands in a small ocean basin or through rifted continental crust during the late Permian; (d) lawsonite- and pumpellyite-bearing metavolcanic blocks incorporated in a Cretaceous tectonic melange, and originally erupted as alkali basalts on oceanic islands in the Hawasina basin; and (e) unmetamorphosed tholeiites formed at a spreading centre in the Hawasina basin and preserved in the Hawasina thrust sheets. A reconstruction of the tectonic history of Saih Hatat based on these data suggests that continental rifting took place in the Permian, developing two distinct basins separated by rifted continental material. Some of the basaltic blocks that formed in the outboard Hawasina basin were tectonically dislocated and incorporated into a tectonic melange formed in a foredeep during the early stages of obduction. Emplacement of the Semail ophiolite onto the continental margin resulted in high-pressure, low-temperature metamorphism of this melange and the underlying units.

Formation and exhumation of blueschists and eclogites from NE Oman: new perspectives from Rb–Sr and 40Ar/39Ar dating

“…1 The garnet blueschists and epidote amphibolites of zone C appear to have the same protoliths as the crossite–epidote schists and greenschists of zone A, as indicated by the geochemical data of El‐Shazly et al . (1994, 1997).…”

“…1 The garnet blueschists and epidote amphibolites of zone C appear to have the same protoliths as the crossite-epidote schists and greenschists of zone A, as indicated by the geochemical data of El-Shazly et al (1994. The persistent occurrence of Cpx-rich granofels within the mafic unit, as well as layers of quartz-mica schists, metapelites and calcareous mica schists in all three metamorphic zones, suggests that the same units occur throughout Region III, and were folded, boudinaged and metamorphosed under different P-T conditions in the different zones.…”

Cambrian metamorphic complexes in Tasmania: Tectonic implications

“…However, sub‐ophiolitic metamorphic rocks formed under similar conditions have been reported from Tertiary arc–continent collision zones in the Philippines (Encarnacion et al 1995) and Proterozoic metamorphic complexes in East and West Africa (Bernard‐Griffiths et al 1991; De Souza Filho & Druru 1998). In most island‐arc–continent collisions and ophiolite obductions (including the low temperature New Caledonian and Oman metamorphics) the protolith was a mixture of passive margin, continent‐derived sedimentary rock and tholeiitic mafic volcanics (El‐Shazly et al 1994; Aitchison et al 1995).…”