Spinel as the most stable crystalogeraphic phases against serpentinaziation in peridotites of Baft ophiolite mélange in Kerman province

Subject Areas :

Nadie Mohammadi ¹ , Hamid Ahmadipour ² , Sima Peighambari ³

1 - دانشجوی کارشناسی ارشد پترولوژی دانشگاه شهید باهنر کرمان
2 - استادیار دانشگاه شهید باهنر کرمان
3 - دانشجوی دکترای پترولوژی دانشگاه شهید باهنر کرمان

Received: 2016-09-07 Accepted : 2016-09-07 Published : 2011-03-21

Keywords: Spinel, Baft ophiolite mélange, Serpentines, Serpentinization, chromite,

Abstract :

Baft coloured mélange with approximate area 617 km2, is located along Baft and Shahr-e-Babak major faults insouth of Kerman province. Field and microscopic studies on peridotites, chromitites and related dunites in thisarea indicate that they are formed in mantle environment. Because peridotites in this mélange have been deeplyaltered (serpentinized), primary minerals such as olivine and pyroxene have been changed into secondaryminerals, spinels are only resistant primary minerals against alteration in these rocks that has been survived incompletely serpentinized rocks. In this study, chemical compositions of spinels' unaltered cores have been usedfor the petrogenesis and tectonic setting of the studied peridotites and chromitites. Based on evidences, thestudied lithologies can be divided into two groups. The first group is peridotites include harzburgite, dunite andlherzolite that belong to Alpian type peridotites and the harzburgites, probably resulted from 15-20 percentpartial melting of a fertile lhrzolitic mantle. Second groups are chromitites for which a magmatic genesis couldbe assumed. The studied chromitites are podiform and their parental magma is boninite. The chromites withaverage Cr2O3=62.8% and Cr#=0.83 are classified as Cr-rich chromitites or as the first grade type chromites inthe world. Cr# and Mg# values indicate that the studied chromitites have been crystallized from boninitemagmas, probably in suprasubduction zone setting in a back arc environment.