Seafloor metasomatism associated with oceanic detachment in supra-subduction zone ophiolite: evidence from the Western Limassol Forest Complex, Troodos

Seafloor mantle exhumation along detachment faults is well known from slow to ultra-slow spreading ridges, i.e. oceanic core complex, and from magma-poor margins at ocean-continent transitions. It is also thought to occur in supra-subduction zone environment (SSZ) although the detachment architecture and associated magmatism, deformation and metasomatism are still poorly understood. The Western Limassol Forest Complex (WLFC), in the Troodos ophiolite, Cyprus, is characterized by extensive mantle rock exhumation associated with complex magmatism, extensive metasomatism and ultramafic-hosted volcanogenic massive sulfide mineralizations. The exhumation of mantle rocks in the WLFC has been interpreted to be the result of a poly-tectonic evolution, including transform fault-related deformation along the Arakapas transform fault during the Cretaceous, overprinted by Miocene thrusting associated with the Yesavara thrust belt. However, new field observations, together with structural and geochronological data from the WLFC indicate that the initial exhumation of the mantle sequence occurred along an earlier Cretaceous detachment fault.Ultramafic rock metasomatism in the WLFC is dominated by serpentinization but other seafloor-like metasomatisms, such as sulfide and magnetite mineralizations as well as carbonation are also present. Preliminary in-situ calcite and magnetite U-Pb dating by LA-ICP-MS give ages ranging between 85.6 ±12 Ma and 92±2 Ma for seafloor metasomatism in the WLFC. In this contribution we present an overview of seafloor metasomatism preserved in the WLFC using field, petrographic and geochemical evidences, and discuss how it relates to mantle exhumation during the early stages of the Troodos ophiolite evolution. The WLFC detachment, although strongly overprinted by transform and thrust-related deformations appears to be one of the few well-preserved oceanic detachments in an SSZ environment worldwide.