Mineralogy and composition of chromitites and host peridotites from the Colkahan ultramafic complex (Nazdasht mine), Kerman, southeastern Iran

作者：Najafzadeh Ali Reza^*

来源：Mineralogy and Petrology, 2017, 111(3): 337-350.

DOI：10.1007/s00710-016-0479-6

• Podiform chromitites
• Supra-subduction zone setting
• Colkahan ultramafic complex
• Paleogeodynamic setting
• Iran
• Kerman

Several chromitite pods of variable sizes are hosted in dunite-harzburgite of the about 14 km(2) mining district of Nazdasht, in the Colkahan ultramafic complex, located in the Haji Abad-Esfandagheh district in the Kerman province, southeastern Iran. Olivine, orthopyroxene, and to a lesser extent clinopyroxene of a highly refractory nature, are the primary silicates found in the dunites and harzburgites. The matrix minerals between chromian spinel grains are serpentinized olivine and pyroxene, Cr-rich chlorite (kaemmererite), uvarovite, and veins of magnesite. Chromian spinel mainly occurs as massive chromitite pods and as thin massive chromitite bands together with minor disseminations in dunites and harzburgites. Chromian spinels in massive chromitites show relatively high Cr-numbers (0.60-0.82), Mg-numbers (0.54-0.74) and very low TiO2 contents (averaging 0.16 wt.%) which may reflect the crystallization of chromite from a boninitic magma. The Fe3+-number is very low, down to < 0.17 wt.%, in the chromian spinel of chromitites and associated peridotites of the Colkahan ultramafic complex. The harzburgite and dunite contain accessory chromian spinel with Cr-numbers of about 0.66 and 0.69, respectively. The Colkahan dunites and harzburgites are high depleted with low CaO (0.01-0.47 wt.%) and Al2O3 (0.29-0.64 wt.%) compared to primitive mantle.
The chemical and mineralogical characteristics of these chromitites have a strong affinity to podiform chromitites in the mantle section of supra-subduction zone ophiolites. Calculated parental melts of the chromitites and geochemical discrimination diagrams based on mineral chemistry of peridotites are consistent with the differentiation of arc related magmas with boninitic affinity and support the supra-subduction paleogeodynamic setting of Haji Abad-Esfandagheh district previously proposed by some authors.

• 出版日期2017-6