Reuben J. Hansman1, Richard Albert2, Axel Gerdes2, and Uwe Ring1

1) Department of Geological Sciences, Stockholm University, SE-106 91 Stockholm, Sweden

2) Department of Geosciences, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany

Simplified geological map of the central Al Hajar Mountains, Oman (adapted from Le Métour et al.

Direct dating of brittle structures is challenging, especially abso- lute dating of diagenesis followed by a series of superimposed brittle deformation events. We report 22 calcite U-Pb ages from tectonites and carbonate host rocks that date 3 diagenetic and 6 brittle deforma - tion events. Results show that U-Pb dating of calcite fibers from these structures is compatible with overprinting relationships. Ages indicate that diagenesis occurred between 147 ± 6 Ma and 103 ± 34 Ma, and was followed by top-to-the-south, layer-parallel shearing due to ophio - lite obduction at 84 ± 5 Ma (2 σ errors). Sheared top-to-the-northeast, layer-parallel veins were dated as 64 ± 4 Ma and are interpreted to have developed during postobduction exhumation. After this event, a series of strike-slip structures, which crosscut and reactivated older faults due to northwest-southeast horizontal shortening, were dated as 55 ± 22 Ma and 43 ± 6 Ma. Eight ages from strike-slip faults and thrusts resulting from northeast-southwest shortening range from 40.6 ± 0.5 Ma to 16.1 ± 0.2 Ma. The youngest ages are from minor overprint - ing fibers ranging in age between 7.5 ± 0.9 Ma and 1.6 ± 0.6 Ma. Our results show that U-Pb dating of calcite fibers can be successfully used to constrain a complicated succession of brittle deformation structures that encompasses two orogenies and an intervening extension period.

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