Tectonic and metamorphic evolution of the Temsamane units, External Rif (northern Morocco): implications for the evolution of the Rif and the Betic-Rif arc

Journal of the Geological Society, Jul 2007 by Negro, F, Agard, P, Goff�, B, Saddiqi, O

Conclusions

This study provides new constraints on the evolution of the External Rif and the geodynamic evolution of the Betic-Rif arc by deciphering the tectonometamorphic evolution of the Temsamane units.

Parts of the Temsamane units recorded MP-LT metamorphic conditions in the range 7-9 kbar and 330-430 �C. These conditions are very similar to those reported for the shallowest HP-LT Alboran Domain units and reflect a rather low burial metamorphic gradient of 13-15 �C km-1 typical of subduction zones. These units are characterized by a coherent deformation regime with roughly east-west stretching and top-to-the-west shear sense accompanying the exhumation of the whole Temsamane massif. The age of the metamorphic peak is not well constrained but could be Oligocene (Moni� et al. 1984; Negro 2005). The main exhumation stage of the Temsamane units occurred during the Middle Miocene (c. 15 Ma) and continued under brittle conditions until the Messinian.

To account for this MP-LT metamorphic imprint, two main hypotheses can be put forward: Hypothesis 1 involves an internal origin, with the MP-LT Temsamane units having been subducted together with the Sebtides; Hypothesis 2 involves an external origin, implying the existence of a transient Mesorifan subduction zone, approximately parallel to the main one in the Alboran Domain but located somewhat to the south. At the scale of the entire Rif, however, the late tectonometamorphic evolution of the Temsamane units strongly differs from that of the Sebtide units and resembles the Middle to Late Miocene east-west extension observed in the core of the internal Betics, on the other side of the Alboran Sea. We tentatively relate this late evolution to the onset of westward slab retreat in the Alboran region during the Early Miocene.

The French-Moroccan programme 'Action Int�gr�e MA/01/13' and the CNRS-INSU are gratefully acknowledged for financial support during field and laboratory work. We warmly thank R. Caron for the quality and the number of thin sections. We are grateful to D Frizon de Lamotte and G. Booth-Rea for their constructive reviews, and to T. Needham for his constructive comments on the manuscript.

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