Cr-spinel Mineral Chemistry from Sawlava Ophiolite Complex, Kurdistan, NW Iran, Geotectonic Setting Implication

Bahman Rahimzadeh , Fariborz Masoudi , Amir Ali Tabbakh Shabani
Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran.
Faculty of Earth Sciences, Kharazmi University, Tehran, Iran.


Abstract

Ophiolitic ultramafic rocks associated with chromitite lenses are studied in
detail from Sawlava ophiolitic complex along the Zagros suture in the northwest of Iran.
Except one small window in Miana village almost all primary silicates in dunites and
wehrlites have been altered to serpentine; however, Cr-spinel is the surviving phase left.
Chemistry of the Cr-spinel minerals from small chromitite lenses within the ultramafic
units provides information about the primary petrological characteristics. The Cr# of the
Cr-spinels is between 0.76 to 0.82 in chromitite lenses, 0.58 to 0.67 in dunite and 0.49 to
0.52 in wehrlite. Al2O3 values and FeO/MgO ratio in the chromitite lenses indicate a
boninitic melt for the source magmas of the Cr-spinels. The low values of Ti and high
contents of Al and high Cr# in peridotite Cr-spinels reveal a pronounced rate of partial
melting (25-35%) for peridotites. This suggests that Sawlava complex source was mantle
wedge with elevated degrees of partial melting. Olivine, clinopyroxene and Cr-spinel
mineral chemistry shows the characterization similar to those in abyssal to supra-
subduction zone (SSZ) peridotites which suggest a fore-arc basin setting for the
generation of the chromitite lenses from Sawlava ophiolites.

Key Words:
Cr-Spinel,
Chromitite, Sawlava
ophiolitic complex,
Zagros, Iran


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