Paleotethys-related water-rocks interactions in gabbros of the Anarak ophiolite (Central Iran): constraints from mineralogy and geochemistry

Abstract

The Anarak Paleozoic ophiolite with nearly east-west trend is located in the western part of the Central-East Iranian Microcontinent (CEIM). There are some leucocratic gabbros which are found as stocks and dykes and cross-cut the Anarak ophiolite. The studied gabbros are composed of clinopyroxene, amphibole, biotite, plagioclase, chlorite, epidote, garnet, sphene, apatite, prehnite, calcite, magnetite and ilmenite.

Presence of a very high amount of hydrous minerals in the studied rocks reveal high activity of H₂O in the involved fluids. Very low values of HREEs and light color of the studied gabbros indicate a non-peridotitic source rock. Geochemical features of the studied rocks indicate the melting of a mafic protolith.

These hydrous phases are possible products of the reaction between oceanic crust and the fluids of seawater derivation, rich in calcium ingredients. Ingression of seawater through the oceanic crust and its downward penetration into the gabbros, caused the dissolution of a large amount of Ca and alkali components. At the lower, the Ca was added to the gabbro and produced new Ca-rich minerals.

The Anarak samples show geochemical signatures of melts derived from a subducted oceanic slab. Distinct trace-element signatures, show the similarity of the studied gabbros to "adakite-like" rocks. According to the age and location of the studied gabbros, it is suggested that the primary magma of the studied gabbros should be created by partial melting of Paleo-Tethys subducting oceanic crust.