2 HIGH-PRESSURE METAMORPHIC EVENTS IN NE OMAN - EVIDENCE FROM 40AR 39AR DATING AND PETROLOGICAL DATA

The Saih Hatat tectonic window in NE Oman exposes basement and shelf units that structurally underlie the Semail ophiolite. These units were metamorphosed under high-pressure conditions, as evidenced by the occurrence of lawsonite schists, carpholite-bearing metasediments, blueschists, and eclogites. Conventional K-Ar and 40Ar/39Ar dating of whole rocks and white mica separates from the structurally highest Region I of Saih Hatat and the lowest-grade blueschists of the northern part of the structurally lowest Saih Hatat Region III yield ages of 72-80 Ma. White micas from the high-grade blueschists and eclogites of Region 111, which formed at T > 340-degrees-C, yielded variably discordant age spectra with weighted mean "plateau" ages of 106-111 Ma. The age data, combined with structural and petrological criteria, suggest that many units exposed in Saih Hatat experienced two high-pressure, low temperature (high P/T) metamorphic events. The first, in the Early Cretaceous, was possibly a result of partial subduction of the continental margin beneath a microcontinental fragment of Gondwanaland. The second high P/T event was a result of the Late Cretaceous emplacement of the Semail ophiolite onto the oman continental margin and is characterized by lower temperatures.