Magnetic anisotropy of a sub-ophiolitic metamorphic sole (Mersin ophiolite, Turkey)

Abstract

The Mersin ophiolite of southern Turkey is a well-exposed, Late Cretaceous, Neo-Tethyan supra-subduction zone ophiolite. It is underlain by metamorphic sole rocks inferred to have formed at the top of a down-going plate during subduction. These have a well-developed foliation and lineation observable in the field (defined by the preferred orientations of hornblende and plagioclase crystals). Here we present the first magnetic fabric data reported from the Mersin ophiolite with such settings. Anisotropy of low field magnetic susceptibility ellipsoids in sampled amphibolites have clustered, NW-plunging minimum principal axes representing poles to a SE-dipping magnetic foliation that aligns with the macroscopic metamorphic foliation plane seen in the field. Maximum AMS principal axes define a SE-plunging magnetic lineation that is parallel to the macroscopic metamorphic lineation. Oblate magnetic fabrics at specimen-level and an overall triaxial fabric at locality-level in these rocks are consistent with the development of the dominant metamorphic fabric by a combination of pure shear flattening and simple shearing during the formation and exhumation of the Mersin sole rocks. These observations are compatible with a recent tectonic model for the evolution of the ophiolite based on paleomagnetic data that invokes flattening and exhumation of the down-going slab in an incipient subduction zone during supra-subduction zone spreading.