Abstract

An ophiolitic tectonic mélange occurs to the S and structurally below pre-Permian crystalline rocks of the Bitlis Massif in SE Turkey. Basic igneous rocks occur in the mélange as tectonic blocks in a sheared serpentinite matrix and most have recrystallized during metamorphism or metasomatism. The basic rocks once formed part of a single igneous complex subsequently disrupted to form the mélange. The volcanic rocks and cherts were metamorphosed under conditions transitional between the blueschist and epidote-amphibolite facies. The mineralogy of the basic schists is dependent on composition: blueschists (crossite + magnetite ± chlorite ± phengite) differ from greenschists (hornblende + chlorite ± biotite) in having higher Fe/Fe + Mg and Fe3+/(Fe3+ + Fe2+). In contrast, the gabbros were metamorphosed under greenschist facies conditions and the resulting amphibolites are characterized by static fabrics and contain actinolite rather than hornblende. Later calcium metasomatism produced rodingites. It is suggested that the greenschist facies metamorphism was a sub-ocean-floor event and the higher pressure metamorphism occurred during subduction. The thrusting during the later stages of compression in the orogenic belt led to the emplacement of the mélange in its present position, but played little part in its formation.

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