K-Ar ages of metamorphic rocks at the base of the Samail ophiolite, Oman

Journal Article · Fri Apr 10 04:00:00 EST 1981 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB086iB04p02777· OSTI ID:6536698

Lanphere, M A

Hornblendes from amphiobolities in the sheet of metamorphic rocks beneath the peridotite member of the Samail ophiolite and phyllites farther from the peridotite contact have weighted mean /sup 40/Ar//sup 39/Ar total fusion ages of 90.0 +- 3.0 m.y. and 79.5 +- 3.0 m.y., respectively. The amphibolities represent the first tectonic slice welded to the base of the Samail ophiolite after it was detached from the Tethyan oceanic crust. Formation of the amphiobolities occurred no more than 3 to 7 m.y. after crystallization of plagiogranite in the ophiolite. The phyllites represent another tectonic slice of ocean floor sediments welded to the ophiolite as it was transported further from the Tethyan spreading axis. The K-Ar ages suggest, assuming a half-spreading rate of 2 to 5 cm/yr, that detachment of the Samail ophiolite and formation of amphibolite facies rocks occurred no more than 60 to 350 km from spreading center. Using the same spreading rate, one can calculate a minimum half width of 300 to 750 km for the Tethyan Ocean during the Late Cretaceous.

• Research Organization: U. S. Geological Survey, Menlo Park, California 94025
• OSTI ID: 6536698
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 86:B4; ISSN JGREA
• Country of Publication: United States
• Language: English

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