The petrography and mineral chemistry of the metamorphosed lherzolite in Darreh-Deh massif (east of Nain Ophiolite, Central Iran) is investigated in order to find the calcium source for rodingitization and tremolitization. In comparison with olivine and orthopyroxene, the clinopyroxene
has lower modal content and is more alteration-resistant. The microprobe data and petrography of these lherzolites indicate that Ca2+ cations can be released during serpentinization of orthopyroxene (with ~18 vol% and CaO~2.7 wt%) and clinopyroxene (with ~6 vol% and CaO~ > 20
wt%). In contrast, per- vasive serpentinization of mantle olivine with ~70 vol% and CaO~0.02–0.07 wt% is another expected source for producing Ca2+ rather than metamorphic olivine with CaO~ < 0.02 wt%. The released Ca2+ cannot be completely accommodated in crystal
lattice of produced serpentine (with CaO~0.02–0.06 wt%), talc and chlorite (with CaO~0.015 wt%), but it can participate in formation of Ca-bearing tremolite (CaO~13 wt%), as a result of serpentinization of clinopyroxenes or subsequent metamorphism of peridotites at amphibolite facies
and in formation of coarse-grained clinopyroxene blades and tremolite during rodingitization. Therefore, the calcium content in clinopyroxene, orthopyroxene and olivine of a plagioclase–free peridotite is a potential source of Ca2+, depending on the degree of serpentinization
or chloritization.
Mineral Chemistry Perspective of Nain Ophiolite Mélange, Central Iran
