Geochemistry of ophiolitic mafic rocks from south of Orzouieh (Kerman, Iran)

Ophiolites are considered to provide fundamental clues about geodynamic evolution and magmatic processes which are responsible for the formation of ancient oceanic basins and surrounding continental areas. Iranian ophiolites are parts of eastern Tethyan ophiolite belt along with Alpine- Himalayan orogenic system. Stocklin (1974) classified Iranian ophiolites into 4 main groups: a) ophiolites of the Main Zagros Thrust Zone (MZTZ) including Neyriz and Kermanshah ophiolites, b) ophiolites of Northwest of Iran including Khoy ophiolites, c) ophiolite and colored mélange belt including Shahrebabak, Chehel Kureh, Sabzehvar, Baft, d) ophiolites of Northern Iran along the Alborz range. Esfandagheh-Haji Abad district, located in a tectonically active area, make up southeastern parts of the MZTZ and Sanandaj-Sirjan belt. Ophiolitic complexes along the MZTZ record geodynamic evolution of Southern Neo-Tethys ocean. This distric comprises highly deformed metamorphic rocks, colored mélange and several ultramafic massifs. South of Orzuieh, well preserved culmulate mafic rocks are seen along with metamorphic rocks and ophiolitic mélange. They have sheared boundaries with underlied lithologies such as ultramafic rocks and ophiolitic mélange. They also tectonically overlied by Sargaz-Abshur metamorphic complexes including marbles and amphibolites. The cumulate sequences start at the bottom with ultramafic cumulates and pass up into gabbroic rocks. Basal melanocratic ultramafic cumulates mainly characterize by sheared and myllonitized textures. Porphyroclasts and crushed fragments of these cumulates have been observed in faulted lower boundary. The rhythmic layering are considerable to the upper parts of these section, so that variable amounts of plagioclase and mafic minerals have been seen in olivine gabbro continued to gabbro, leucogabbro and anorthosite. The thickness of the melanocratic and leucocratic layers differs to the upper layer; there are thicker leucogabbro and anorthosite layeres at the top. Numerous micro-gabbroic-diabasic dikes intrude both types of cumulative rocks.The mafic cumulates consisting mainly olivine gabbro, gabbro, gabbronorites leucogabbro. The mafic cumulative rocks present cumulus textures such as adcumulus, mesocumulate, and orthocumulate ones. Olivine gabbros consist mainly 65 vol. % calcic plagioclase, clinopyroxene 13 vol.%, olivine 15 vol.%, orthopyroxene 6 vol.%. Plagioclase show deformed twining and partly altered to sausaurite association. Gabbronorites include cinopyroxene 20 vol.%, orthopyroxene (hyperstene) 30 vol.%, plagioclase 48 vol.%. The leucogabbros are made of 80–90 vol.% cumulus euhedral calcic plagioclase and 10–20 vol.% clinopyroxene.The chonderite-normalized REE patterns of different mentioned mafic cumulates from south of Orzuieh, show general depletion from heavy to light REE with distinct positive Eu anomalies. These patterns are similar to those of other oceanic gabbros and gabbros from ophiolitic complexes. Eu positive anomalies, are classically interpreted as a typical feature of plagioclase accumulation in early cumulates and consistent with the high anorthite content of plagioclase. The geochemical characteristics of these cumulate mafic rocks are representative of their oceanic lithospheric nature.