uncorrected proofs Serpentinization and chloritization of metamorphosed lherzolites in Darreh-Deh (east of Nain Ophiolite, Central Iran): Calcium source for rodingitization and tremolitization Nargess Shirdashtzadeh 1 , Ghodrat Torabi 2 With 4 figures and 4 tables Abstract: 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 com- parison 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 Ca 2+ 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 Ca 2+ rather than metamorphic olivine with CaO~ < 0.02 wt%. The released Ca 2+ 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 par- ticipate 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 Ca 2+ , depending on the degree of serpentinization or chloritization. Key words: calcium; peridotite; tremolitization; serpentinization; rodingitization 1. Introduction In peridotites, calcium is mostly known to be derived from the decomposition of the pyroxenes into serpentine (Capedri et al. 1978, Muraoka 1985, Frost & Beard 2007, Bach & Klein 2009), which can be liberated into the rod- ingitization fluids and react to change the magmatic min- eralogy of basic(mafic) dikesrocks cutting the ultramafic bodies) or gabbroic rocks juxtaposed to serpentinizing peridotite by a tectonic process (e.g., Sabzehei 2002). Rodingites are Ca-rich and Si-poor hydrated calc-silicate rocks found within the serpentinized ultramafic (lower) sections of ophiolites and within the altered sections of oceanic plates (e.g., by Bell et al. 1911, Coleman 1966). They act as Ca traps because of the great stability of di- opside and garnet at low SiO 2 activities (Bach & Klein 2009). Although calcium is one of the key elements in the mineralogy of rodingites, in most cases the latter gen- erally have no spatial relationship with calcareous rocks (e.g., Rice 1983, Li et al. 2004, Mohammad & Maekawa 2008, Piber & Tropper 2010, Shirdashtzadeh et al. 2014). In fact, Ca-rich hydrothermal fluids or leached Ca-rich fluids by serpentinization and metasomatic processes in the mafic and ultramafic rocks are known as the major calcium source for rodingitization (e.g., Thayer 1966, Coleman 1977, Hall & Ahmed 1984, Schandl & Mittwede Authors’ addresses: 1 Department of Geology, Faculty of Science, University of Isfahan, P.O. Box: 8174673441, Isfahan, Iran; nshirdasht@sci.ui.ac.ir; ORCID: 0000-0002-2379-9797 2 Department of Geology, Faculty of Science, University of Isfahan, P.O. Box: 8174673441, Isfahan, Iran; torabighodrat@sci.ui.ac.ir; ORCID: 0000-0002-4952-2614 E © 2019 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany www.schweizerbart.de DOI: 10.1127/njma/2019/0163 0077-7757/2019/0163 $ 3.25 N. Jb. Miner. Abh. (J. Min. Geochem.) 000/0 (2019), 000–000 Article published online October 2019