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

Volume 1 , Issue 1 , January 2016 , Pages 419-436

Authors

¹ Faculty of Earth Sciences, Shahid Beheshti University, Tehran, Iran.

² Faculty of Earth Sciences, Kharazmi University, Tehran, Iran.

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.

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