An Exotic Eclogite/Blueschist Slice in a Barrovian Style Metamorphic Terrain, Alanya Nappes, Southern Turkey

Abstract

A 600 m thick, more than 40 km long slice of eclogite facies rocks, called the Sugözü Nappe, occurs in the Alanya area, southern Turkey, sandwiched between two other crystalline nappes which do not show HP/LT metamorphism. All three nappcs were affected by a later Barrovian-type metamorphism and penetrative deformation which welded the nappes into a single tectonic unit. The SugOzu Nappe consists predominantly of garnet-mica schists with lenses of eclogite and blueschist metabasites. The mineral assemblage in the eclogites, garnet+omphacite+glaucophane+paragonite+quartz+phen gite+rutile, is estimated to have formed at 13·5±1·5 kb and 510±25°C. The eclogite assemblage is variably overprinted by a later Barrovian metamorphism with the development of barroisite, chlorite, and albite. The extent of the Barrovian overprint was controlled by the supply of fluid to the rocks. The Barrovian metamorphism increases in grade downwards in the structural sequence; biotite and garnet isograds are mapped in the lowermost Mahmutlar Nappe, made up mostly of metapelites and metapsammites. The metapelites in the garnet zone consist of garnet+biotite+chlorite+muscovite+albite+oligoclase+quartz+ilmenite; metamorphic conditions are estimated as 6·5±1·0 kb and 469±13°C. The HP/LT rocks of the Sugözü Nappe underwent a cooling of about 100°C during a dry uplift from a depth of about 48 km to 21 km where they were intercalated with the other nappes, and affected by a Barrovian metamorphism caused by the incoming fluids. The case of the Alanya Nappcs illustrates that the Barrovian overprint observed in many eclogites and blueschists may not be due to increasing temperature during uplift, but simply due to the introduction of a fluid phase during part of the uplift P-T path.