Petrology of gabbroic rocks of mawat ophiolite complex (central sector)‎, ne Iraq

Abstract EN

The gabbroic members of the igneous rocks from the Mawat Ophiolite Complex are located in the Zagros Suture Zone at the boundary between the Arabian and Iranian Plates.

They are related to post collision event with emplacement into the continental crust after collision (during Tertiary) between the Arabian and Iranian Plates.

Three types of gabbroic rocks were recognized and studied: 1) The layered gabbros, which are the dominant type; 2) The marginal gabbros are the most affected by alteration and deformation among the three types of the gabbros, and 3) The dyke pegmatoid gabbros.

The layered gabbros exhibit two types of layering; compositional layering and grain size layering.

Mechanical crystal settling is considered as the main process of layering.

In this study, the petrographic study of 100 thin sections showed that these rocks consist of calcic plagioclase, bytownite in composition (An 85), clinopyroxene (augite) and rarely orthopyroxene, as the major mineral phases.

Iron oxides, mainly magnetite is found as an accessory primary phase and as secondary after the Fe-Mg bearing mineral phases.

The rocks in general, experienced alteration with the formation of different secondary minerals.

Amphibole (Tremolite – Actinolite) is abundant as alteration product of the primary pyroxenes; associated with chlorite, epidote, sericite and secondary magnetite.

Plagioclase attained relatively variable degrees of alteration.

Three types of deformations were recognized; crystal-plastic, semi-brittle and brittle.

Pseudomorphic and non-pseudomorphic alterations were distinguished.

The marginal gabbros are most affected by alteration and granulation.

Primary magmatic textures include hypediomorphic granular, intergranular, poikilitic, ophitic and sub ophitic textures, whereas deformation textures are evident by granulation, secondary twinning, and schistose textures.