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Gondwana Research 12

Evolution of the Central Iranian basement

Alireza Nadimi

Geology Department, Payame Noor University of Isfahan, Kohandej, PoB. 81465-617, Isfahan, Iran

Received 21 October 2005; accepted 18 October 2006Available online 8 December 2006

Abstract

Most of the Infracambrian–Lower Paleozoic sedimentary rocks occurring in Iran cover a crystalline basement. In Central Iran, and the Saghandregion along the Chapedony and Poshte Badam faults, the basement complexes show structural vestiges of Precambrian deformational,depositional, erosional, metamorphic and magmatic events. In this region, the basement complexes contain the Chapedony, Poshte Badam, BonehShurow and Tashk formations. The prevailing metamorphism, from low grade to high grade, is pre-Pan African Orogeny (i.e. from 2400 to570 Ma). The presence of greenstone belts, a paleo-suture zone and ophiolitic rocks (i.e. from 2100 to 1500 Ma) around the high-grademetamorphic rocks of the Chapedony Formation, provide evidence that cratonization forming the Iranian basement occurred during the Paleo- andMesoproterozoic. After formation of the basement complexes, metamorphism of the Precambrian formations and establishment of the Arabo–Iranian coherent platform at the end of Pan African Orogeny, Central Iran broke up during a Neoproterozoic–Early Cambrian extensional tectonicregime. Infracambrian–Phanerozoic sedimentary rocks were then deposited on the basement complexes. The Iranian basement complexes areextensively overprinted by Pan African Orogeny and younger igneous events.© 2006 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

Keywords: Central Iran; Precambrian basement; Cratonization; Paleo-suture; Pan African Orogeny

1. Introduction

The Iranian plateau extends over a number of continentalfragments welded together along suture zones of oceaniccharacter. The fragments are delineated by major boundaryfaults, which appear to be inherited from earlier geologicaltimes. Each fragment differs in its sedimentary sequence,nature, and age of magmatism and metamorphism, and instructural character and intensity of deformation. This paperdescribes the evolution and effects of Precambrian orogenicphases in Central Iran.

The continental crust of Iran was metamorphosed, grani-tized, folded and faulted during the Late Precambrian by thePan African Orogeny. Metamorphosed rocks, which arescarcely exposed, form the basement of the region (Stocklin,1968, 1974; Nabavi, 1976; Berberian, 1976) and this orogenicphase, considered by many authors to be an episode of platecollision, terminated between 600 and 550 Ma in Arabia

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(Brown and Coleman, 1972; Greenwood et al., 1975; Frischand Al-Shanti, 1977). Following these movements the UpperPrecambrian–Cambrian Hormoz salt was deposited in basins,parts of which now lie along the north and eastern side of theArabian Peninsula.

Since the different orogenic phases recognized in thecrystalline shield of Arabia (Greenwood et al., 1976) are notrecognized in Iran, no detailed correlation can be made betweenthe basements of Iran and Arabia. Hence they may havedifferent pedigrees and the consolidation of Iranian basement isnot well understood. The Precambrian Chapedony and PoshteBadam formations of east Central Iran, which consist of meta-greywacke, meta-diorite, meta-andesite, amphibolite, pyroxe-nites, serpentinite, and calc-alkaline intrusive rocks, mayrepresent the crust of a Precambrian calc-alkaline island arc(Stocklin, 1972; Haghipour, 1974, 1977; Berberian and King,1981). If this interpretation is correct the nearly north–southarcuate mountain belts in east Central Iran could represent theoriginal pattern of the Precambrian arcs.

After the metamorphism of the Precambrian formations andthe establishment of the Arabo–Iranian platform at the end of

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325A. Nadimi / Gondwana Research 12 (2007) 324–333

Pan African Orogeny, compressional tectonic activity endedwith intrusion of granites and alkaline volcanism. The UpperPrecambrian alkali-enriched Doran granites of Iran seem to beequivalents of the ∼ 600 Ma younger granites of Arabia(Stocklin et al., 1964; Schmidt et al., 1973, 1978; Sillitoe,1979). The Doran granite cuts the Upper Precambrian low-grade metamorphic rocks of the Kahar Formation and iscovered by Lower Cambrian sediments (Stocklin et al., 1964).

The Late Precambrian volcanics also include andesite, basaltand tuff. These widespread “post-orogenic” volcanic rocks,which overlie the Precambrian metamorphic rocks and areoverlain by Neoproterozoic–Cambrian sediments, may be thesignature of rifting of the Arabo–Iranian continental crust duringa phase of extensional tectonism associated with formation ofthe epicontinental platform from Arabia to Alborz prior todeposition of the Upper Precambrian–Cambrian succession.Following Late Precambrian (Pan African) orogeny and con-solidation of the basement, the Precambrian craton of Iran,Pakistan, central Afghanistan, southeastern Turkey and Arabiabecame a relatively stable continental platform with epiconti-nental shelf deposits (mainly clastics) and exhibited a lack ofmajor magmatism or folding. This regime presumably lasteduntil Late Paleozoic times, although some epirogenic move-ments occurred in Late Silurian–Early Devonian times (Berber-ian, 1983).

2. Basement complexes in Central Iran

The term “basement complex” is used here for the set of rocksunderlying the Pan African unconformity and comprisingmostly metamorphic or igneous rocks (with the age of thebottom of the related rock cover being variable, ranging in mostcases from 570 to 550 Ma). These basement complexes showstructural vestiges of old Precambrian deformational, deposi-tional, erosional, metamorphic andmagmatic events. The relatedold features are more or less modified by younger deformationaland thermal overprints.

Precambrian terranes are exposed in many places of Iran(Fig. 1). In the Saghand Region, Central Iran, basement com-plexes occur as the oldest lithostratigraphic element (Nadimi,2005).

2.1. Central Iran

The Central Iranian Terrane is surrounded by fold-and-thrustbelts, within the Alpine–Himalayan orogenic system of westernAsia. It is located between the Turkish syntax to the west and theAlborz and Kopeh–Dagh Ranges to the north, the Zagros andMakran Ranges to the west and south and the East Iran Ranges tothe east. Being situated to the northeast of the Zagros–MakranNeo-Tethyan suture and its sub-parallel Cenozoic magmatic arc(Urumieh–DokhtarMagmatic Arc), the Central Iranian Terrane isan area of continuous continental deformation in response to theongoing convergence between the Arabian (Gondwana) andEurasian (Turan) plates (Figs. 1 and 2).

The Central Iranian Terrane consists, from east to west, ofthree major crustal domains: the Lut Block, Tabas Block and

Yazd Block (Alavi, 1991) (Fig. 2) separated by a series ofintersecting regional-scale faults. The Lut Block is locatedbetween the Nehbandan Fault to the east and Nayband Fault tothe west. The Tabas Block is surrounded by the Nayband Faultto the east and the Kalmard and Kuhbanan Faults to the west.The Yazd Block is located between the Kuhbanan Fault to theeast, the Biabanak Fault to the north and the Rafsanjan andShahre Babak Faults to the south and west.

Although the stratified cover rocks can be correlated betweenthe different blocks, locally significant facies and/or thicknessvariations occur across the domain boundaries. The easternregion of the Yazd Block, between the Yazd and Tabas blocks,provides remarkable exposures of the deeper sections of theCentral Iranian platform strata, among which Late Neoproter-ozoic and Lower Paleozoic rocks are abundant. Interestingly,the type localities of all of the Precambrian to Carboniferousformations in greater Central Iran (Stocklin and Setudehnia,1977) have been selected from within this relatively narrowbelt. The crystalline rocks that underlie the above formationshave been uplifted and widely exposed in the vicinity of thetown of Saghand.

2.2. The Saghand Region

The Saghand Region closely follows the trends of thepredominant fault structures of the Central Iranian Terrane,many of which are seismically active or were active in the nearpast. Three first-order fault systems are identified within theCentral Iranian Terrane: a north-trending system (e.g. Naybandand Nehbandan faults), a northeast system (e.g. Poshte Badamand Kalmard faults) and a northwest system (e.g. Kuhbanan andRafsanjan faults). A combination of strike–slip (right-lateral)and reverse (thrust) movements associated with these faults hasgenerated a complex pattern of regional deformation involvingcrustal shortening, horizontal block rotation and localized uplift(Jackson and McKenzie, 1984). The Saghand region, inparticular, is situated at the intersection of northeast and north-west trending fault systems where the most extensive docu-mented outcrops of basement rocks in Central Iran are exposed(Ramezani and Tucker, 2003).

In the Saghand Region, there are three roughly NNE-trending lithotectonic domains, bordered from east to west bythe Poshte Badam, Chatak and Chapedony faults, respectively(Fig. 3a). Rocks of the Eastern Lithotectonic Domain rangefrom lower-amphibolite-facies gneisses (Boneh Shurow For-mation) to virtually unmetamorphosed sedimentary rocks,whereas, the Western Lithotectonic Domain is dominated byhigh-grade gray gneisses and migmatites (Chapedony Forma-tion). Rocks of the Central Lithotectonic Domain include avariety of metamorphic rocks (Poshte Badam Formation) andigneous plutons by and large different from those in the othertwo domains. Each lithotectonic domain contains a suite ofplutonic rocks of distinct age distribution ranging in lithologyfrom granite to quartz–diorite and, locally, diorite. In this re-gion, basement complexes are about 10 km thick; they underliethe Infracambrian unconformity and contain the Chapedony,Poshte Badam, Boneh Shurow, and Tashk formations (Fig. 4).

Fig. 1. Geodynamic map of Central Iran and adjacent regions. Solid rectangle indicates the Saghand region. Outcrops of Precambrian rocks are numbered: 1 –Chapedony; 2 – Poshte Badam; 3 – Bafq; 4 – Mute; 5 – Golpayegan; 6 – Aligodarz; 7 – Zanjan; 8 – Karaj Valley; 9 – Gorgan.

326 A. Nadimi / Gondwana Research 12 (2007) 324–333

Gravimetric studies in Central Iran show that the continentalcrust thickness is 40 to 48 km (Dehghani and Markis, 1983).

2.2.1. The Chapedony FormationThis formation, located mainly between the Chapedony

Fault to the west and the Chatak Fault to the east, is the oldestbasement complex in Iran. The Chapedony Formation is com-posed predominantly of a variety of high-grade gneisses andassociated migmatites (Hushmandzadeh, 1969; Haghipour andPelissier, 1977), including rocks of granulite facies, and isbordered by rocks of greenschist facies or lower grade at theeastern side. Both types are intruded by younger granitic

plutons. Reported 207Pb/206Pb zircon ages of the ChapedonyFormation range from 2140.9 Ma to 48.2 Ma (Ramezani andTucker, 2003) and Rb/Sr whole rock ages are around 2382 Ma(Haghipour, 1974).

The Chapedony Formation occurs in three main outcrops:the Kalute Chatak, Kalute Chapedony and Neybaz Mountain(Fig. 3a). The formation is approximately 4000 m thick andcontains schist, amphibolite, marble, quartzite, gneiss, ribbongneiss, migmatite, anatectic granite and scapolitic rocks allshowing migmatitic textures. Gneiss and granite formed at thelower levels of the Chapedony sequence probably from sedi-mentary protoliths called the “Old Series” (which is not seen on

Fig. 2. Simplified structural map of Central Iran and constituent crustal blocks (compiled from Jackson and McKenzie, 1984; Alavi, 1991; Ramezani and Tucker,2003). Rectangle delineates the study area of Fig. 3.


the surface) during the Chapedonian high-grade metamorphism(Haghipour, 1974).

2.2.2. The Poshte Badam FormationThe diverse assemblage of mainly dark-colored, medium-

grade, metamorphic rocks exposed to the west of the PoshteBadam Fault is known as the Poshte Badam Formation(Haghipour and Pelissier, 1977). The main body of the formation

in the northern part of the Central Domain overlies high-graderocks of the Chapedony Formation along the Chatak Fault(Fig. 3a and b). A variable association of greenstones, schists,meta-greywacke, marble, gneisses, amphibolites, pyroxenites,serpentinite, meta-basalt and conglomerate comprises the bulk ofthe Poshte Badam Formation and it is severely disrupted as theresult of thrusting and by intrusion of granitoid plutons; hence thedispersed outcrops of the formation generally lack continuity.

Fig. 3. (a) Geological map of the Saghand Region (modified after Haghipour, 1977). (b) and (c) cross sections from the basement complexes.


Fig. 5. Gondwana reconstruction in Late Proterozoic time. Precambrian cratonsare drawn by thick line and abbreviated: MT = Menderes–Taurus Block, Ar =Arabian, Af = African, Am = South American, In = Indian, An = Antarctic andAu = Australian plates (modified from Ramezani and Tucker, 2003).

Fig. 4. Generalised stratigraphic section of the basement complexes in theSaghand region.


In addition to the intercalated dolomitic marble layers withinthe Poshte Badam Formation, there are massive crystallinemarble sheets that form many crests and hilltops in the northernpart of the Central Domain. Close field examination indicatesthat the latter are almost invariably in thrust contact with rocks(for example, greenstones) of the Poshte Badam Formation andtherefore should be considered as a separate lithologic unit(Ramezani and Tucker, 2003). The presence of meta-mafic andmeta-ultramafic rocks induced some geologists in the past toconsider the Poshte Badam Formation as an oceanic crust–mantle transition (Haghipour, 1974).

2.2.3. The Boneh Shurow FormationThe Boneh Shurow Formation is the most widely exposed

metamorphic unit of the Eastern Domain with ridge-formingoutcrops directly adjacent to, and to the east of, the PoshteBadam Fault (Haghipour and Pelissier, 1977; Ramezani andTucker, 2003). The formation has four main outcrops in thePoshte Sorkh, Boneh Shurow, Zamanabad and Polo mountains(Fig. 3). It is about 2000 m thick and exhibits a distinct meta-morphic layering composed of an alternation of pink quartzo-feldspathic gneisses, greenish-gray mica–schists and dark-colored amphibolites.

The predominant mineral assemblages of the Boneh Shurowschists together with the presence of epidote (and/or clinozoi-site) and garnet in many of the Boneh Shurow rocks areindicative of lower amphibolite (epidote–amphibolite) meta-morphic facies. Field and petrologic evidence suggests that thebulk of the Boneh Shurow Formation must have formed byemplacement of granitic intrusions as sills into a stratified,predominantly siliciclastic–argillaceous sequence with localmafic volcanic–tuffaceous intervals. The age of the BonehShurow Formation is in the range from 617 Ma to 602 Ma(207Pb/206Pb zircon ages) (Ramezani and Tucker, 2003). Zirconfrom the highly mylonitized Sandikli Granite in the same areayielded Pb–Pb ages ranging from 1924 Ma to 543 Ma, with thelatter being interpreted as the age of granite intrusion (Krönerand Sengor, 1990). The Sandikli Granite in the Menderes–

Taurus Block in southern Turkey, thus presents a good matchfor the Boneh Shurow granitic gneiss in the Saghand region(Fig. 5).

2.2.4. The Tashk FormationThe well-stratified sequence of weakly metamorphosed,

sedimentary and volcanic/ volcaniclastic rocks that occur to theeast of, and sub-parallel to, the Boneh–Shurow Formation isknown as the Tashk Formation (Haghipour and Pelissier, 1977).The exposed section of the formation in its type locality atTashk Mountain is estimated to reach about 2000 meters. Theformation has four main outcrops: the Poshte Sorkh, Tashk,Zamanabad and Polo mountains (Fig. 3).

The bulk of the Tashk Formation consists of dark greenish-gray greywackes, schist, quartzitic schist, quartzite, marble,amphibolite, gneiss, slaty-shale, sandstone locally interbeddedwith arkosic arenites, argillites, tuffaceous deposits and newlyidentified interlayers of basaltic lava. The contacts of the TashkFormation with the Boneh Shurow Formation, where adequatelyexposed, are (thrust) faults (Fig. 3a and c). The Tashk Formationreflects extensive, terrigenous sedimentation, similar to that in amarginal outer shelf/slope environment in proximity to activevolcanic centers. The albite–epidote–actinolite assemblage ofthe Tashk metabasalts is characteristic of greenschist metamor-phic facies. The age data delimit the overall depositional age ofthe Tashk Formation between 627 Ma and 533 Ma (207Pb/206Pbzircon ages) (Ramezani and Tucker, 2003), the latter being theintrusion age of the oldest granitic plutons (for example, ArizGranodiorite, south of study area highlighted in Fig. 1) emplacedinto the formation.

The weakly metamorphosed siliciclastic rocks of the Boz-burun sequence in the Menderes–Taurus Block, share manylithostratigraphic similaritieswith those of the Tashk Formation inCentral Iran. 207Pb/206Pb ages of detrital zircon separated from theBozburun greywackes range from 2522 Ma to 657 Ma (Krönerand Sengor, 1990). The unconformably overlying, fossiliferousMiddle Cambrian sedimentary strata bracket the age of this


sequence between 657 Ma and 533 Ma, fairly similar to the agespan established for the Tashk Formation.

2.2.5. The Infracambrian–Cambrian UnitThe Infracambrian–Cambrian Unit (Volcano–Sedimentary

rocks) refers to an interlayered sequence of largely unmeta-morphosed, intermediate to felsic volcanic rocks, dolomiticlimestones and minor gypsum beds. Outcrops are widespreadon both sides of the Poshte Badam Fault (Fig. 3). Thegeochronologic results clearly indicate an Early Cambrian agefor the volcanic components of this unit. The Infracambrian–Cambrian Unit generally overlies clastic sedimentary rocks ofthe Tashk Formation, although contacts are generally obscuredby deformation, granite intrusion and/or hydrothermal alter-ation. At one isolated location (Douzakh Darreh Mountain),however, the Tashk–Infracambrian–Cambrian Unit contact canbe characterized as a disconformity. The carbonates of theCambrian formations unconformably underlie the lowerCambrian red sandstones and conglomerates (Lalun or DahuFormation) in the Zarigan area as well as in the Bafq region tothe south of the study area (Forster and Jafarzadeh, 1994).

Fig. 6. Schematic sequential diagrams showing evolution of the Iranian basement cosubsequently forming the Chapedony Ocean. (b) Formation of the Chapedony FormaPaleo-to-Mesoproterozoic Poshte Badam Formation. (d) Formation of the BonehNeoproterozoic, Tashk and Kahar Formation. (f ) The Pan African Orogeny in the Nethe Neoproterozoic-to-Early Cambrian.

3. Discussion

Understanding the Precambrian evolution of Central Irandepends on reconstructing the sedimentary, metamorphic andigneous evolution of its basement complex. The prevailingmetamorphism, from low grade to granulite facies, is Pre-PanAfrican (from 2400 to 570 Ma). The oldest known orogeny inIran is the Chapedonian orogeny that metamorphosed the oldersedimentary rocks up to granulite facies. Historically, themetamorphic rocks of the Chapedony Formation have played apivotal role in hypotheses regarding the origin of continentalcrust in the Middle East region. Recognized as the mostintensely metamorphosed rock unit in the polymetamorphicSaghand–Poshte Badam region, the Chapedony formation wasconsidered to represent the Precambrian basement of the Iranianplateau (Hushmandzadeh, 1969; Haghipour and Pelissier, 1977)and was commonly correlated with the Pan African metamor-phic terranes of the Arabian–Nubian Shield. Accordingly, it hasbeen widely stated that consolidation of the basementthroughout the Iranian plateau took place by metamorphismand anatexis between about 1000 and 600 Ma (Stocklin, 1974;

mplexes based on geologic and age data. (a) Gondwana in the Paleoproterozoiction during Chapedonian collision in the Paleoproterozoic. (c) Formation of theShurow Formation during the Meso-to-Neoproterozoic. (e) Formation of theoproterozoic. (g) Extensional movements after the Pan African Orogeny during

Fig. 7. Gondwana reconstruction during the Early Cambrian. Precambriancratons are drawn by thick line explained in Fig. 5. Additional cratons areabbreviated: Ch = South China Block and L = Lhasa Block. Stars refer to Peri-Gondwanan arc plutons (modified from Ramezani and Tucker, 2003).


Berberian and King, 1981; Davoudzadeh et al., 1986). In thefollowing discussion I attempt to demonstrate, based onavailable geologic and age data, the tectonic evolution of theCentral Iranian segment of the Proto-Tethys margin during theLate Precambrian orogenic phases.

The commonly accepted reconstructions of the continents inthe Late Neoproterozoic (see for example, Powell et al., 1980;Lawver and Scotese, 1987; De Wit et al., 1988; McKerrowet al., 1992; Unrug, 1997) invariably place the Indian continentadjacent to the eastern margin of Africa and its Arabian sub-plate, as part of the larger proto-Gondwana supercontinent.Taking into account the necessary edge fits among theGondwanan fragments, the plate reconstructions yield a gapof significant width between the western Indian (Salt Range)and the eastern Arabian (Oman) margins. Regional stratigraphicand paleomagnetic constraints imply that this gap is the mostlikely site for the Central Iranian Terrane within the LateNeoproterozoic proto-Gondwanaland assembly (see Fig. 5).

In the Paleoproterozoic, during an extensional regime, theCentral Iranian segment in the Proto-Tethys margin broke upand the Chapedony ocean basin formed (see Fig. 6a). Duringlater compressional tectonics some subduction zones formed.

Later, the Chapedony Ocean closed and during collisionbetween the Chapedony arc and the continental margin, theChapedony Formation was thrusted and metamorphosed(Fig. 6b). This orogenic phase is called the Chapedonian orog-eny (from 2400 to 2100 Ma).

After emplacement of the Chapedony Formation, the PoshteBadam Formation and accompanying oceanic remnant wereobducted. Serpentinite-decorated faults, thrusts and meta-maficand meta-ultramafic rocks mark sutures between the constituentterranes of Central Iran. These suture traces correlate with theChatak and Poshte Badam Faults (Fig. 6c).

In the Meso-Neoproterozoic, the sedimentary formations ofthe Boneh Shurow formed from erosion of older rocks and werethen metamorphosed (Fig. 6d). Regionally deformed andmetamorphosed sedimentary and granitic rocks of the BonehShurow Formation indicate a Late Neoproterozoic period ofcompression and lower amphibolite facies metamorphism in anorogenic setting.

Subsequently the sedimentary Tashk Formation formed fromerosion of older rocks and was then metamorphosed togreenschist facies (Fig. 6e). Considering its large thickness, atleast a portion of the formation is likely to have been depositedduring the latest Neoproterozoic. Based on lithology and rockfacies, the Tashk Formation must have been deposited in amarginal marine environment, adjacent to centers of basalticand/or pyroclastic eruption (Ramezani and Tucker, 2003).Although the geographic extent of the Tashk Formation is bydefinition limited to the Saghand area, its correlative succes-sions are recognized (or suspected) throughout the Central Iran–Alborz province. These include the Morad Series (Huckriedeet al., 1962), Kalmard Formation (Stocklin, 1968) and the KaharFormation (Dedual, 1967) in the central Alborz Mountains.These occurrences imply that the Tashk facies is widelydistributed throughout the Iranian Plateau and is likely tounderlie Phanerozoic platform strata at depth in many locations.

In the Neoproterozoic, final collision between an activecontinental margin and a passive margin occurred (Fig. 6f ). Inthis collision during Pan African Orogeny the basement forma-tions of Central Iran were metamorphosed (or remetamorphosed).

After collision and metamorphism of the Precambrian for-mations and the establishment of the Arabo–Iranian coherentplatform at the end of Pan African Orogeny in the Neoproter-ozoic–Early Cambrian, in an extensional tectonic regime,Central Iran broke up (Fig. 6g). The extensional tectonic activitybegan with granitic intrusion and alkali volcanism. Late Pre-cambrian post-orogenic volcanics, which are partly the extrusiveequivalents of the Doran granite and are mainly alkali rhyolite,rhyolitic tuff and quartz porphyry, include the Gharadash For-mation in northwestern Iran, the Taknar Formation in theKashmar region, northeastern Iran, the Rizu–Desu Series (orEsfordi Formation) in southeastern Central Iran and the HormozFormation in Zagros. The Late Precambrian volcanics alsoinclude some andesite, basalt and tuff. These widespread post-orogenic volcanics rocks, which overlie the Precambrian meta-morphic rocks, are overlain by Infracambrian–Cambrian sedi-ments and incorporated the stretching of Arabo–Iraniancontinental crust during a phase of extensional tectonism.

During this general rifting and sinking phase in northeasternArabia, theMain Zagros, High-Zagros, Nayband and some othermajor faults appear to have acted as facies dividers separating themain Hormoz evaporitic basin and the coeval dolomite (theSoltanieh Formation) in Central Iran and the Alborz.

Following Pan African Orogeny and the consolidation of thebasement, the Precambrian craton of Iran, Pakistan, centralAfghanistan, southeastern Turkey and Arabia became a rel-atively stable continental platform (Fig. 7) with epicontinentalshelf deposits (mainly clastics) and a lack of major magmatismor folding. This regime presumably lasted until Late Paleozoic


times, although there were some epirogenic movements in LateSilurian–Early Devonian times.

4. Conclusion

The Saghand Region of Central Iran exposes rocks thatcomprise the sub-stratum of the Central Iranian continentalterrane, as part of the larger Alpine–Himalayan orogenic sys-tem. In this region, basement complexes are exposed, un-derlying the Infracambrian unconformity; they contain theChapedony, Poshte Badam, Boneh Shurow, and Tashk forma-tions. The following conclusions based on available geologicand age data are presented:

In the Saghand region along the Chapedony and PoshteBadamfaults, basement complexes occur as the oldest lithostratigraphicelement. During the Chapedonian orogeny of Paleoproterozoicage (from 2400 to 2100 Ma), the oldest basement complexes ofIran formed. The basement complexes weremetamorphosed fromlow- to high-metamorphic grade during compressional tectonicregimes in the Paleo-to-Neoproterozoic (from 2400 to 570 Ma).

The presence of greenstone belts, paleo-suture zones andophiolitic rocks around the high-grade metamorphic rocks of theChapedony Formation show that an island-arc type cratonizationformed the Iranian Precambrian basement. Serpentinite-deco-rated faults, thrusts and meta-mafic and meta-ultramafic rocksmark sutures between the constituent terranes of Central Iran andcorrelate with the Chatak and Poshte Badam Faults.

After forming the basement complexes and metamorphism ofthe Precambrian formations, and the establishment of the Arabo–Iranian coherent platform at the end of Pan African Orogenyduring an extensional tectonic regime in the Neoproterozoic–Early Cambrian, Central Iran broke up and Infracambrian–Phanerozoic sedimentary rocks covered the basement complexes.The Pan African Orogeny and younger igneous events overprintthe Iranian basement complexes.

Acknowledgments

I thank Ali M. Rajabi of Islamic Azad University, MahallatBranch for his constant support of my research and also I thankHassan Nadimi of Payame Noor University of Isfahan whohelped me in the field. The help of Prof. W. Frisch, Prof. R.A.J.Trouw and an anonymous reviewer and Dr. V.K. Singh ofBundelkhand University through helpful reviews is gratefullyacknowledged.

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