Ultramafic Nain Iran

The 1 st International Applied Geological Congress, Department of Geology, Islamic Azad University - Mashad Branch, Iran, 26-28 April
2010
Petrography and mineralogy of ultamafic rocks in Nain Ophiolite

(Central Iran)
Mohammad Foudazi 1 Mohammad Hashem Emami2 Soleiman Alai Mahabadi2
1-IslamicAzad University,Science and Research Branch
2-Geological Survey Of Iran

Mail:foudazim@yahoo.com
Abstract
This area has been divided into three geological units,:An ophiolitic mélange zone consisting a
mixture of ophiolite, limestone and radiolarites trending North- North west through the middle of the
area; A Tertiary volcanic zone in the west; A Tertiary sedimentary zone in the east (Davoudzadeh,
1976; Alaie Mahabadi&Foudazi,2005).The ophiolitic mélange zone consist of ultramafic rocks,
isotropic gabbros,diabasic dikes,sheeted dikes,pegmatoid gabbroic dikes,pillow lavas and sheet
flows,radiolarian cherts and pelagic limestone which have Upper Cretaceous microfunas, and
metamorphic rocks are amphibolites and gloucophan schists(Alaie Mahabadi &Foudazi;2006,2009).
The ultramafic rocks consist of peridotite predominately tectonised harzburgite that locally grade
into lherzolite,harzburgitic dikes bearig plagioclase, serpentinite, wherlitic dikes,dikes of dunite and
pyroxenite.
In petrographic study most of the harzburgite have granular,xenomorphic granular,schistose, and
mylonitic texture.In the eastern part of the ophiolitic melamge zone one to several kilometer
harzbugite bodies with very low lenses of dunite are situated along the major North-North west
trending faults.In these rocks olivine are partly serpentinised(chrysotile and lizardite)and
clinopyroxene have been very low altered to tremolite-actinolite, chlorite and talc.
Harzburgites consist of olivine(Fo93.76Fa6.23),orthopyroxene(En89.9Fs8.4Wo1.56),exsolution lamellae of
clinopyroxene(En48.3Fs3.7Wo47.9),and subhedral to euhedral chrom spinels.
Lherzolites have porphyroblastic texture;they consist of olivine,orthopyroxene,clinopyroxene,and Cr-
spinel.
Harzburgitic dikes bearing plagioclase have been cut serpentinised peridotites and isotropic
gabbros.These rocks have cumulate texture,and consist of olivine (Fo94Fa6) ,orthopyroxene
(En86.43Fs10.5Wo3.0.6 ) in rim to (En89.31Fs7.81Wo2.87) in center and very low plagioclase(anortite).
Serpentinites formed by sepentinisation of various kinds of peridotite(spetially harzburgites) and
essentially occur as a main of the mélange in this area.These rocks have mesh texture is well
developed by alteration of olivine(Forsterite).In serpentinites occurrence of bastite derived from total
alteration of orthopyroxene is distigushed.
Dunite can be found as thin dikes or in lenticular form in harzburgite,and consist mostly of
olivine(Fo92.15Fa7.33).
Wherlite and pyroxenite(webstrite-olivine webstrite)occure as small dikes in this ophiolitic melange
zone and have been cut isotropic gabbros and sheeted dikes. Pyroxenite have granular texture,and
consist of orthopyroxene,clinopyroxene and very low serpentinised olivine in olivine websterits.
Pyroxenites have been cut isotropic gabbroes consist mostly of clinopyroxene(En50.6Fs7.2Wo42.1) and
orthopyroxene(En86.3Fs10.6Wo2.9),and pyroxenite have been cut sheeted dikes consist of
clinopyroxene(En52.7Fs6.2Wo41.41) and orthopyroxene(En89.05Fs7.9Wo2.9).
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The 1 st International Applied Geological Congress, Department of Geology, Islamic Azad University - Mashad Branch, Iran, 26-28 April 2010
Introduction
Iran enjoys a unique stance in terms of ecological and geological issues. Remains of the
oceanic crusts (Ophiolites), Thethys and Neothethys found in different parts of the country
including North of Nain (Central Iran), Eastern Iran (Birjand, Nehbandan, Zahedan),
Northeastern Iran (Torbat Heidarieh, Fariman, Sabzevar), Western Iran (Khoy), Southern Iran
(Esfandagheh, Minab), and Northeastern Iran (Mashad )(Fig.1)
Geological map of ultramafic and maficrocks in Iran( Pessagno, E.A; Ghazi, A.M; Kariminia ,M;
Duncan,R.A; and Hassanipak, A.A;( 2005)(Fig.1)
Satelite map of Nain Ophiolite and ophiolitic melang ; Tertiary volcanic zone in the west; A tertiary
sedimentary zone in the east(Fig.2)
Geology
The Nain ophiolite comprise of mantle and crustal sequences.The mantle sequence
consist of lherzolite, harzburgite which mark mantle deformation , cut across by plagioclase-
bearing harzburgite, wherlite and pyroxenite dikes and dunitic pods.
The isolated diabasic dike cut all of the mantle sequence.The plutonic part of crustal sequence
contain isotropic gabbro, diabase sheeted dike complex and pegmatite gabbro.The extrusive
sequence comprise of pillow lavas and sheet flows, radiolarite, chert and pelagic limestone
which have Upper Cretaceous microfunas.
Fig.1)Serpentinization in peridotites Fig.2)Mantle deformation in harzburgites

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Fig.3)Field aspect of harzburgite Fig.4) Dunite lenses in mantle peridotites
Petrography and mineralogy of ultramafic rocks

In Nain Ophiolite serpentinite rocks has mesh texture(Fig 5a), and serpentinisation has been
taken place in two phases in harzburgenite tectonised rocks. In the first phase,
serpentinisation has been occurred in a static condition and no mechanical transformation has
taken place in these rocks. In the second stage, serpentinisation has been occurred with
dynamic phase resulting from pressure of faults which has formed cracks and crevice and the
non-economic mineral of asbest is replaced in little amount inside veins and veinlets. Mineral
such as magnesite, chromite, amphibole and talc are in relation with these rocks. These
minerals have been formed in different temperatures and pressures.
base of the microscopic studies, most of harzburgite have granoblastic and porphyroclastic
textures which confirm their mantle deformation(Fig5c). Olivine is partly serpentinized,
chrysotile and lizardite and clinopyroxene is fresh but locally altered to tremolite-actinolite,
chlorite and talc.
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0.25m b 0.25m a
0 25m d 0.5m c
0.5m f 0.5m e
Fig 5. (a) Mesh texture in serpentinite peridotites.(b)Olivine cut across by carbonate

vienlet in serpentinised harzburgites.(c)Porphyroclastic harzburgite showing a deformed
orthopyroxene porphyroclast with kink band,under crossed nichols.(d) Porphyroclastic
harzburgite showing exulution lamellae of clinopyroxene in orthopyroxene crystal.(e)Unhedral
chrom spinel in serpentinised peridotites.(f)Cumulate texture in plagioclase bearing
harzburgitic dikes
In harzburgite the microprobe analysis of minerals indicate that the olivines mostly have
forsterite composition (Fo93.76Fa6.23). The orthopyroxene have enstatite (En89.9Fs8.4Wo1.56), bear
exsolution lamellas of clinopyroxene with diopside composition (En48.3Fs3.7Wo47.9)(Fig5d). The
Cr-spinel formed as subhedral to euhedral.
The plagioclase-bearing harzburgitic dikes have cumulate texture, and consist of olivine with
forsterite composition (Fo94Fa6), orthopyroxene with enstatite composition(En86.43Fs10.5Wo3.0.6).
The plagioclase have anortite composition (AN=90). Dunite have granular to granoblastic
texture and mostly composed of olivine with forsterite composition (Fo92.15Fa7.33).
Pyroxenites have granular texture, and consist of orthopyroxene, clinopyroxene and very low
serpentinized olivine. The clinopyroxene have diopside composition from
(En50.6Fs7.2Wo42.1) to (En52.7Fs6.2Wo41.41) and orthopyroxene have enstatite composition from
(En86.3Fs10.6Wo2.9) to (En89.05Fs7.9Wo2.9).
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Conclusion
Olivine with high grade mantle deformation(Fo%90-93), Orthopyroxene(En%89) bearing
exsolution lamellas of clinopyroxene with diopside composition (En48.%), subhedral and
unhedral Cr- spinel, very low elementes in microprobe study specially Nicle Oxide from
Olivine in harzburgites and dunite(NiO=0.04wt%), Aluminium Oxide(Al2O3=2.8-3.4wt%),
Titanium Oxide(TiO2=0.015-0.04wt%), (Na2O=0.16-0.4wt%)and (K2O=0.045wt%) show that
mantle sequence of Nain Ophiolite is dominated by residual lherzolite.
The chondrite- normalized spider diagram of harzburgite show a depleted soure for Nain
peridotite but the cross cutting peridotite with cumulative character are moderately enriched.
Refrences
Alai Mahabadi,S., Foudazi,M., 2006. Geology and Petrography of Nain ophiolite(Central Iran) ,Six
International Symposium on Eastern Mediterranean Geology page 47
Alai Mahabadi,S., Foudazi,M., 2003. Geological map of Nain Quadrangle,Scale 1/100,000,
Geological Survey Of Iran
Coleman,R.G.1977.Ophiolites,Ancient oceanic lithosphere? Minerals and Rocks: New York,Springer
verlag , New York 229p.
Davoudzdeh,M.,1972.Geology and petrography of the area north of Nain,central Iran.Geol.Surv.report
No 14.
Ghasemi,H.,Juteau,T.,Bellon,H.,Sabzehi,M.,Whitechurch,H.,Ricou,L.E., 2002. The mafic-ultramafic
complex of Sikhoran(Central Iran) : a polygenetic ophiolite complex.
Juteau,T.,Maury,R.,1999. "The Oceanic crust, from accretion to mantle recycling", Springer-
Praxis,Chichester,UK,390 p.
Lippard , S.J.; Shelton ,A.W. & Gass ,I.G , 1986. The ophiolite of Northern Oman. Geol. Soc. London.
Mcm. II , 178P.
Technoexport.,1984:Geological map of Ashin Quadrangle,Scale 1/100,000 , Geological Survey Of
Iran
Willson, M.1989. Igneous petrogenesis , A global tectonic approach , chapman et Hall edit ., Londres,
466p.
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The 1 st International Applied Geological Congress, Department of Geology, Islamic Azad University - Mashad Branch, Iran, 26-28 April

Petrography and mineralogy of ultamafic rocks in Nain Ophiolite

Mohammad Foudazi 1 Mohammad Hashem Emami2 Soleiman Alai Mahabadi2

1-IslamicAzad University,Science and Research Branch

2-Geological Survey Of Iran

Fig.1)Serpentinization in peridotites Fig.2)Mantle deformation in harzburgites

Fig.3)Field aspect of harzburgite Fig.4) Dunite lenses in mantle peridotites

Petrography and mineralogy of ultramafic rocks

Fig 5. (a) Mesh texture in serpentinite peridotites.(b)Olivine cut across by carbonate

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