3.a.1. Kermanshah ophiolite

This is the NW-most outer belt ophiolite in Iran. The ophiolite trends NW–SE and is distributed in two regions, separated by the SSZ metamorphic rocks (see Fig. A1 in online Appendix 1 at http://journals.cambridge.org/geo). The ophiolite is exposed over ~ 2400 km², essentially SW of the MZT (Fig. 2). It is bordered to the NE by SSZ metamorphic rocks and to the SW by Bisotun limestone, a ~ 3 km thick carbonate sequence of Late Triassic to Late Cretaceous (Cenomanian) age, as well as by the Triassic to Cretaceous Kermanshah radiolarites and then by ZFTB sedimentary rocks. The Kermanshah ophiolite is thrust over the Bisotun limestone. Initial thrusting of the Kermanshah ophiolite is thought to have occurred during Maastrichtian–Paleocene time, as evidenced by ophiolitic clasts in the Maastrichtian–Paleocene Amiran Conglomerate Formation of the ZFTB (J. Braud, unpub. Ph.D. thesis, Univ. Paris-Sud, France, 1987). This episode of erosion may also correspond to when SSZ rocks were exhumed. This thrust was reactivated in Miocene time, as indicated by the presence of Miocene flysch below the ophiolite (Agard et al. Reference Agard, Omrani, Jolivet and Mouthereau2005).

Two oceanic domains, the Harsin sub-oceanic basin to the south and the Neo-Tethys to the north are proposed for the evolution of the Kermanshah ophiolite (Wrobel-Daveau et al. Reference Wrobel-Daveau, Ringenbach, Tavakoli, Ruiz, Masse and Frizon de Lamotte2010). In this new model, the Harsin basin is suggested to have resulted from mantle exhumation and detachment faulting at two different times: Early Jurassic and early Late Cretaceous (Cenomanian). The later extensional regime could correlate with tectonic movements indicated by Aptian–Albian olistostromes in Neyriz oceanic sediments, the Pichakun nappe (Robin et al. Reference Robin, Gorican, Guillocheau, Razin, Dromart, Mosaffa, Leturmy and Robin2010). Moreover, there may be a younger nappe stack of gabbros, intrusive rocks and pelagic sediments, emplaced during Late Eocene time on the top of the former Cretaceous ophiolite (Wrobel-Daveau et al. Reference Wrobel-Daveau, Ringenbach, Tavakoli, Ruiz, Masse and Frizon de Lamotte2010).

The Kermanshah ophiolite has not been studied much. The presence of scattered dykes with island arc tholeiite (IAT) affinity is reported by Desmons & Beccaluva (Reference Desmons and Beccaluva1983). Some diabasic dykes yield ⁴⁰K–⁴⁰Ar ages of 83–86 Ma (Delaloye & Desmons, Reference Delaloye and Desmons1980). Ghazi & Hassanipak (Reference Ghazi and Hassanipak1999) reported mantle peridotites, gabbro and both island arc tholeiitic and alkaline lavas. Recently Allahyari et al. (Reference Allahyari, Saccani, Pourmoafi, Beccaluva and Masoudi2010) described mantle peridotite, normal mid-ocean ridge basalt (N-MORB)- to enriched mid-ocean ridge basalt (E-MORB)-type gabbroic sequences and scarce pillow lavas at Sahneh (NE of Kermanshah). Not all mafic gabbros are ophiolitic, for example undated pegmatitic gabbro south of Sahneh is probably the westernmost part of a 5 × 10 km E–W gabbro-volcanic belt of Eocene age shown by Allahyari et al. (Reference Allahyari, Saccani, Pourmoafi, Beccaluva and Masoudi2010).

The Upper Cretaceous Kermanshah ophiolite comprises mantle and crustal igneous rocks. The crustal sequence is distinguished by a sheeted dyke complex and a well-developed sequence of pillow lavas; crustal gabbros are missing (see Fig. A2 in online Appendix 1 at http://journals.cambridge.org/geo). Mantle peridotites including harzburgite, depleted lherzolite and pervasively impregnated harzburgite intruded by pegmatite gabbro lenses are found along the Harsin to Noor-Abad road. Another outcrop of depleted lherzolites and harzburgites is SSW of Sahneh (Allahyari et al. Reference Allahyari, Saccani, Pourmoafi, Beccaluva and Masoudi2010). Harzburgites contain serpentinized olivines, large orthopyroxene porphyroclasts, minor clinopyroxene and tiny grains of chromite. Interstitial undeformed plagioclase blebs and unstrained intergranular clinopyroxene are abundant in impregnated harzburgites, where they occur as melt-crystallized phases between pyroxene and olivine porphyroclasts. These minerals and millimetre-size gabbro-noritic aggregates indicate impregnation of harzburgite by melts with the composition of the low-pressure peridotite eutectic (e.g. Piccardo et al. Reference Piccardo, Zanetti, Spagnolo and Poggi2005; Pearce et al. Reference Pearce, Barker, Edwards, Parkinson and Leat2000). Depleted lherzolites have minor clinopyroxene and are considered to represent residual MORB mantle (Allahyari et al. Reference Allahyari, Saccani, Pourmoafi, Beccaluva and Masoudi2010). Ultramafic–mafic cumulate rocks are not observed.

Sheeted dyke complexes, including early basaltic and basaltic-andesitic-diabasic dykes and late dacitic-rhyolitic dykes, are found near Kherran and Sartakht villages (Fig. 3b, c). Each dyke (usually < 0.5 m, locally > 1 m thick) has been injected into others (Fig. 3c); locally plagiogranitic patches are observed as screens between dykes. Diabasic dykes are porphyritic with plagioclase phenocrysts and microlites. Magnesio-hornblende and/or clinopyroxene are also common. The felsic dykes are clearly younger as they cut the mafic dykes. Felsic dykes are composed of feldspar, quartz and amphibole phenocrysts and a cryptocrystalline to spherulitic groundmass. Relative abundances of felsic to mafic dykes are 1:3 to 1:2. A well-preserved volcanic sequence and sheeted dyke complex is found in many places e.g. near Kherran and Sartakht villages, especially near 47°E. Near the Kherran village, there is a ~ 200 m thick volcanic pile including (from bottom to top) poorly phyric basaltic-andesites, basaltic lavas and pillowed basalts (Fig. 3a). Pillow lavas contain clinopyroxene, altered plagioclase microlites and tiny titanomagnetites set in an altered glassy groundmass. The volcanic pile is capped by a thin basaltic lava flow. Locally, basaltic flows contain thin plagiogranitic veins.

Figure 3.

Field photographs of Zagros outer belt ophiolites (approximate positions shown in Fig. A10 in online Appendix 1 at http://journals.cambridge.org/geo). (a) Pillow lava sequence of the Kherran to Sartakht section (Kermanshah ophiolite). (b) Sheeted dyke complex in the Kherran to Sartakht section (Kermanshah ophiolite). Late felsic dykes injected into early mafic dykes. (c) Close-up view of contact between dykes in sheeted dyke complex (Kermanshah ophiolite). (d) Upper Cretaceous pillow lava sequence near Siah-Pareh village (section C of Fig. A10 in online Appendix 1 at http://journals.cambridge.org/geo) (Kermanshah ophiolite). (e) Close-up view of fragmented pillow lavas in Dowlat-Abad, Neyriz ophiolite. (f) Tale-Afshari sheeted dyke complex in the Neyriz ophiolite. Late felsic dyke injected into early mafic dyke. (g) Upper Cretaceous boninitic pillow lavas near Avenan village, Haji–Abad ophiolite. (h) Calc-alkaline pillow lavas with intercalation of Upper Cretaceous pelagic limestones near Chale-Mort village (Haji–Abad ophiolite).

The base of the volcanic pile SSE of Sartakht village consists of pillowed basalts intruded by diabasic dykes that grade down into a sheeted dyke complex. Dykes include some that are andesitic and amphibole-bearing diabasic. Near Siah-Pareh village, there is a > 5 km² region composed of a thick sequence of pillow lavas and basaltic flows (Fig. 3d).

3.a.2. Neyriz ophiolite

The Neyriz ophiolite (see Fig. A3 in online Appendix 1 at http://journals.cambridge.org/geo) was first defined as the High Zagros ophiolite–radiolarite belt by Berberian & King (Reference Berberian and King1981). There are three imbricated sheets, from bottom (SW) to top (NE), the Pichukan series, mélange units and ophiolite (Ricou, Reference Ricou1971, Reference Ricou1976; L. E. Ricou, unpub. Ph.D. thesis, Univ. Paris-Sud, France, 1974; Ricou, Braud & Brunn, Reference Ricou, Braud and Brunn1977). The Pichakun series (Ricou, Reference Ricou1968) consists of Upper Triassic limestone, Middle Jurassic oolitic limestone and Lower–Middle Cretaceous conglomeratic limestone, representing Neo-Tethys pelagic sediments (analogous to the Bisotun limestone and radiolarites of Kermanshah). The Pichakun series is wedged between two thrust sheets of sheared mélange (Pamić & Adib, Reference Pamić and Adib1982; Babaie et al. Reference Babaie, Ghazi, Babaei, La Tour and Hassanipak2001). Above the Pichukan series, the mélange consists of exotic blocks of Permian–Triassic Megalodon-bearing limestone associated with radiolarites, pillow lavas with alkaline (M. Arvin, unpub. Ph.D. thesis, Univ. London, 1982) and tholeiitic (Babaie et al. Reference Babaie, Babaei, Ghazi and Arvin2006) characteristics, serpentinites and metamorphic rocks. The upper mélange is tectonically overlain by ophiolite slices, and both ophiolite and mélange thrust sheets are transported over Cenomanian–Turonian shallow water shelf/platform carbonates (Sarvak Formation; Alavi, Reference Alavi1994). The contact of the lower mélange with the underlying autochthonous Sarvak Formation is marked by a mylonitic amphibolite sole (Babaei, Babaie & Arvin, Reference Babaei, Babaie and Arvin2005).

Ophiolite thrust sheets cover about 1500 km². These are unconformably overlain by uppermost Cretaceous anhydritic limestones of the Tarbour Formation (James & Wynd, Reference James and Wynd1965). The Neyriz ophiolite was thrust over the Pichakun and mélange sheets in Turonian to Maastrichtian time (e.g. Ricou, Braud & Brunn, Reference Ricou, Braud and Brunn1977; Alavi, Reference Alavi1994; Babaie et al. Reference Babaie, Babaei, Ghazi and Arvin2006), exposing and allowing erosion of the ophiolite and accumulation of such clasts in Upper Cretaceous–Paleocene conglomerates (Haynes & Reynolds, Reference Haynes and Reynolds1980; Lanphere & Pamić, Reference Lanphere and Pamic1983). This episode of erosion may correspond to when SSZ rocks were exhumed, as evidenced by the presence of SSZ clasts in Upper Cretaceous–Paleocene conglomerates (Sabzehei, Reference Sabzehei1996).

The Neyriz ophiolite is composed of mantle and crustal units capped by Upper Cretaceous (Cenomanian–Turonian to lower Santonian) pelagic sediments. The mantle sequence is represented by depleted to highly impregnated harzburgites containing screens of residual dunite, podiform chromitite, pyroxenitic sills/dykes, pegmatite gabbros, gabbroic dykes/sills, isotropic melano-gabbros and diabasic-basaltic-andesitic dykes (see Fig. A2 in online Appendix 1 at http://journals.cambridge.org/geo). Diabasic dykes contain highly altered plagioclase and clinopyroxene. Isotropic melano-gabbros are characterized by plagioclase, orthopyroxene, clinopyroxene, brown amphibole, minor sulfides and titanomagnetite. Dunitic dykes/sills are common through the Neyriz mantle sequence. At the top of the mantle sequence there are highly impregnated peridotites including layered leucogabbro, olivine-bearing melanogabbro and pyroxenite cumulate sills and lenses. These lenses intrude mantle peridotites (see Fig. A2 in online Appendix 1 at http://journals.cambridge.org/geo) and contain olivine, slightly altered plagioclase, clinopyroxene and fine-grained sulfide. Marble and skarn-type rocks are found at the contact of these intrusions with depleted harzburgite and on the top of gabbroic dykes (see Fig. A2 in online Appendix 1 at http://journals.cambridge.org/geo) suggesting they formed when hot peridotite intruded Upper Triassic platform limestones during continental rifting (Hall, Reference Hall1980) and/or via interaction with high-temperature fluids released from gabbroic dykes intruding peridotite (M. R. Jannessary, unpub. Ph.D. thesis, l'Univ. de Louis Pasteur, France, 2003).

Coarse-grained melano-gabbros containing plagiogranitic pockets overly the mantle sequence. These rocks consist of serpentinized olivine, plagioclase and clinopyroxene showing cumulate texture. A highly fragmented sheeted dyke complex is widespread in the Tale-Afshari region (Fig. 3f); this includes diabasic-basaltic and dacitic dykes. Although intrusive contacts between dykes are difficult to recognize owing to faulting, some intrusive contacts between dykes and dyke-in-dyke relationships are seen. Pillowed and massive lavas containing chert and Upper Cretaceous pelagic limestone are common (Fig. 3e).

3.a.3. Haji–Abad ophiolite

The Haji–Abad (sometimes called Esfandagheh) ophiolite covers ~ 2000 km². Two ophiolites exist here; an older (more northerly) one of Late Triassic–Cretaceous age (Sikhoran–Soghan complexes; Ghasemi et al. Reference Ghasemi, Juteau, Bellon, Sabzehi, Whitechurch and Ricou2002; Ahmadipour et al. Reference Ahmadipour, Sabzehi, Whitechurch, Rastad and Emami2003), and a younger, Upper Cretaceous Haji–Abad ophiolite (more southerly) near the MZT (see Fig. A4 in online Appendix 1 at http://journals.cambridge.org/geo). The older complex is overlain by marble and amphibolites of the Sargaz–Abshur complex and are intruded by Upper Triassic–Lower Jurassic (K–Ar dating; Ghasemi et al. Reference Ghasemi, Juteau, Bellon, Sabzehi, Whitechurch and Ricou2002) isotropic gabbros. The injection of Middle Jurassic–Cretaceous diabasic dykes was the last igneous event experienced by the older ophiolites (Ghasemi et al. Reference Ghasemi, Juteau, Bellon, Sabzehi, Whitechurch and Ricou2002; Ahmadipour et al. Reference Ahmadipour, Sabzehi, Whitechurch, Rastad and Emami2003). Older ophiolitic lavas have suprasubduction zone geochemical signatures. Formation in a back-arc basin (Ghasemi et al. Reference Ghasemi, Juteau, Bellon, Sabzehi, Whitechurch and Ricou2002) or rift (Ahmadipour et al. Reference Ahmadipour, Sabzehi, Whitechurch, Rastad and Emami2003) has been suggested.

The southern Haji–Abad ophiolite formed in Late Cretaceous time and is highly faulted. The mantle sequence includes depleted harzburgite and residual dunite occasionally foliated with aligned spinel. Podiform chromitites are common within the residual dunite (see Fig. A2 in online Appendix 1 at http://journals.cambridge.org/geo). Porphyroclastic harzburgites contain serpentinized olivine, bastitized orthopyroxene, occasional traces of clinopyroxene and black-brown to pale brown spinels. Dunites have highly deformed olivine porphyroclasts with deformation lamellae and inclusions of black spinel. Leucogabbroic and gabbroic dykes are common in the harzburgites. Metamorphosed diabasic dykes containing amphibole, altered plagioclase, chlorite and epidote cross-cut the mantle harzburgite. Haji–Abad ophiolite crustal sequences are characterized by pillowed and massive lava flows (Fig. 3g, h), overlain tectonically or occasionally stratigraphically by Upper Cretaceous pelagic limestones. Small tonalitic intrusions into the crustal sequence also show fault contacts with serpentinites. A fine-grained plagiogranitic sill cross-cuts the tonalitic intrusions. Highly spilitized metavolcanics with thin layers of pelagic limestone are widespread (Fig. 3h). The Upper Cretaceous Haji–Abad ophiolite is overlain by volcaniclastic sandstone and siltstone turbidites, which are succeeded by basalt flows (see Fig. A2 in online Appendix 1 at http://journals.cambridge.org/geo). Basalts are commonly metamorphosed to greenschist facies, with chlorite, titanite, epidote, calcite and secondary quartz. Plagioclase is altered and clinopyroxene rims are chloritized. Greenschist-facies metamorphism may be related to a Cyprus-type massive sulfide deposit within pillow lavas in the Sheikh-Ali region (Rastad, Miralipour & Momenzadeh, Reference Rastad, Miralipour and Momenzadeh2002). Ophiolitic lavas are overlain by Upper Cretaceous pelagic limestones.

3.b.1. Nain ophiolite

The Nain ophiolite is the NW-most IB massif (Fig. 2) and covers about 600 km² (see Fig. A5 in online Appendix 1 at http://journals.cambridge.org/geo). Davoudzadeh (Reference Davoudzadeh1972) first described it as an Upper Cretaceous–Lower Eocene coloured mélange. Rahmani, Noghreyan & Khalili (Reference Rahmani, Noghreyan and Khalili2007) proposed that the Nain ophiolites formed in a suprasubduction zone tectonic environment, based on the composition of sheeted dykes.

The Nain ophiolite mantle sequence is composed of moderately depleted harzburgites with minor plagioclase lherzolite formed as a result of gabbroic impregnation. Harzburgites have porphyroclastic and/or blastomylonitic texture. Pegmatite gabbros, coarse-grained sulfide-bearing gabbros and isotropic gabbros/gabbronorites are common within the mantle sequence. Pyroxenitic, gabbroic, gabbronoritic and diabasic dykes and sills cross-cut the Nain mantle sequence (Fig. 4a and Fig. A6 in online Appendix 1 at http://journals.cambridge.org/geo). Pegmatite gabbros contain large clinopyroxene and plagioclase crystals. Coarse-grained gabbros locally show alternating plagioclase-rich and clinopyroxene-rich layers. Gabbronorites are cumulates, containing olivine, orthopyroxene, clinopyroxene and plagioclase crystals with minor pyrite. Isotropic gabbros have clinopyroxene, amphibole and variably altered plagioclase crystals. Slices of garnet amphibolite containing leucocratic segregations resulting from partial melting occur in this ophiolite.

Figure 4.

Field photographs of Zagros inner belt ophiolites (approximate positions shown in Fig. A11 in online Appendix 1 at http://journals.cambridge.org/geo). (a) Early rodingitized gabbroic sill in mantle harzburgite of the Nain ophiolite. (b) Injection of diabasic dyke into amphibole gabbros, host of the Nain ophiolite sheeted dyke complex. (c) Isolated diabasic dyke in mantle sequence of the Dehshir ophiolite. (d) Late dacitic dykes injected into early diabasic dykes in the Dehshir ophiolite sheeted dyke complex. (e) Rhyolitic dyke injected into volcanic sequence of the Shahr-e-Babak ophiolite. (f) Interbedded andesitic lavas with Upper Cretaceous radiolarites in the Shahr-e-Babak ophiolite. (g) Basaltic sill within pyroclastic rocks of the Balvard–Baft ophiolite. (h) Pyroclastic unit of the Balvard–Baft ophiolite overlain by Upper Cretaceous pelagic limestones.

The Nain ophiolite crustal sequence includes a sheeted dyke complex and overlying lavas (Fig. 4b and Fig. A6 in online Appendix 1 at http://journals.cambridge.org/geo). The sheeted dyke complex contains mafic and felsic microgabbroic and gabbronoritic dykes with mutually intrusive contacts. These dykes either intrude the host amphibole gabbros/microgabbros (Fig. 4b) and plagiogranites (e.g. near Ahmad-Abad village) or are injected into other dykes (SE of Separo village). Pillow lavas and massive lava flows overlie the sheeted dyke complex. Plagioclase microlites and clinopyroxene are primary minerals of the lavas. Once-glassy lava groundmass is altered into reddish clay.

Globotruncana-bearing Upper Cretaceous (Coniacian–Maastrichtian) pelagic limestones overlie the pillow lavas and are found as thin screens between pillows. Pelagic limestones are unconformably overlain by grey sandy limestones of Palaeogene age (Davoudzadeh, Reference Davoudzadeh1972). A basal conglomerate containing ophiolitic cobbles indicates Early Paleocene uplift and erosion of the ophiolite. Diabasic sills with boninitic affinities intrude Middle to Upper Paleocene limestones (H. Shafaii Moghadam, unpub. Ph.D. thesis, Shahid Beheshti Univ., Tehran, Iran, Reference Shafaii Moghadam, Whitechurch, Rahgoshay and Monsef2009). Small Oligo-Miocene dacitic domes with adakitic signatures cross-cut the Nain ophiolite (H. Shafaii Moghadam, unpub. Ph.D. thesis, Shahid Beheshti Univ., Tehran, Iran, Reference Shafaii Moghadam, Whitechurch, Rahgoshay and Monsef2009).

3.b.2. Dehshir ophiolite

The Dehshir ophiolite is exposed discontinuously over ~ 150 km² near the centre of the IB (Fig. 2 and Fig. A7 in online Appendix 1 at http://journals.cambridge.org/geo). The lavas of this ophiolite are conformably capped by Turonian–Maastrichtian (93.5–65.5 Ma) Globotruncana-bearing pelagic limestones. This ophiolite was first described as part of regional geological mapping (Sabzehei, Reference Sabzehei1997). More detail is presented by Shafaii Moghadam, Stern & Rahgoshay (Reference Shafaii Moghadam, Stern and Rahgoshay2010).

The Dehshir ophiolite mantle sequence includes harzburgite, clinopyroxene- bearing harzburgite and cumulate rocks including plagioclase lherzolite, clinopyroxenite, leucogabbro and pegmatite gabbro (see Fig. A6 in online Appendix 1 at http://journals.cambridge.org/geo). Plagioclase and clinopyroxene are the predominant cumulus phases in pegmatite gabbros. Clinopyroxene is partly converted into tremolite whereas plagioclase is altered into sericite and clay. Plagioclase occurs as large euhedral cumulus grains in leucogabbros and together with clinopyroxene displays coarse-grained granular texture. More rarely plagioclase laths are aligned, defining magmatic foliation. Olivine is interstitial between plagioclase. Accessory phases are titanomagnetite and ilmenite occurring as intercumulus grains.

Diabasic dykes and isotropic gabbros intrude the harzburgite (Fig. 4c). Diabasic dykes are fine- to medium-grained, aphyric to moderately porphyritic with clinopyroxene and plagioclase phenocrysts set in an intergranular groundmass. Plagioclase and clinopyroxene are the main constituents of isotropic gabbros and show intergranular to sub-ophitic textures. Green amphiboles (magnesio-hornblende) and disseminated ilmenites are present in isotropic gabbros.

The Dehshir ophiolite crustal section comprises pillowed basalts, basaltic and basaltic-andesitic massive flows, and a basaltic-dacitic sheeted dyke complex (Fig. 4d). Pillowed and massive lavas are moderately porphyritic, with clinopyroxene and plagioclase phenocrysts set in a glassy groundmass with plagioclase microlites. Albite microlites, K-feldspar and quartz are the main constituents of dacitic dykes in the sheeted dyke complex. Plagiogranite occurs both as dykelets injected into isotropic gabbros and as small plugs emplaced in metamorphic rocks. Plagioclase, orthoclase and anhedral quartz with accessory amphibole and biotite are found in plagiogranite.

3.b.3. Shahr-e-Babak ophiolite

The Shahr-e-Babak ophiolite lies ~ 100 km SE of Dehshir (Fig. 2) and covers ~ 500 km². It is bounded to the west by the Dehshir–Baft fault, to the SSW by Sanandaj–Sirjan metamorphic rocks and to the NNE by the Dehaj–Sarduiyeh magmatic belt (see Fig. A8 in online Appendix 1 at http://journals.cambridge.org/geo), which is part of the Urumieh–Dokhtar arc (Dimitrijevic, Reference Dimitrijevic1973). Faulting, shearing, displacement of ophiolite units and tectonic interleaving with younger units is common. This ophiolite was first described by Dimitrijevic (Reference Dimitrijevic1973) as a result of mapping in the Kerman region. Shahr-e-Babak comprises a complete ophiolite sequence except for a sheeted dyke complex (Ghazi & Hassanipak, Reference Ghazi and Hassanipak2000). Two geochemical signatures are observed: arc-like basalts, andesites and rhyodacites and ocean-island basalt (OIB)-like trachy-andesites. Ghazi & Hassanipak (Reference Ghazi and Hassanipak2000) proposed formation in a narrow oceanic basin that opened between the Central Iranian microcontinent and the SSZ, followed by subduction to the NW.

The Shahr-e-Babak ophiolite mantle sequence is dominated by highly serpentinized harzburgites. Diabasic dykes and isotropic gabbro lenses commonly intrude harzburgite (see Fig. A6 in online Appendix 1 at http://journals.cambridge.org/geo). Isotropic gabbros are common within the mantle sequence as small lenses cut by plagiogranitic veins. The volcanic sequence is composed of basalt, andesite, dacite and rhyolite. These are either massive lava flows or are interbedded (associated with diabasic mafic rocks) with Campanian–Maastrichtian pelagic sediments (Fig. 4f). Massive and pillowed lavas overlie the interbedded volcanic sequence. Rhyolitic dykes and sills cross-cut andesite and basalt near Chah-Bagh village (Fig. 4e). Shallow dioritic-granitic plutons intrude the massive lavas (see Fig. A6 in online Appendix 1 at http://journals.cambridge.org/geo).

Basalts contain altered plagioclase phenocrysts and microlites associated with clinopyroxene. Plagioclase (albite-oligoclase) is the predominant mineral in andesites, < 2% in aphyric andesite and > 20% in porphyritic andesite. Clinopyroxene and amphibole (edenitic to pargasitic hornblende) are also common in andesite. Plagioclase microlites with fine-grained quartz are present in the groundmass of these rocks. Coarse-grained plagioclase and quartz are the main constituents of dacites, with less abundant sanidine and apatite. Spherulitic intergrowth of albite, fine-grained polycrystalline to cryptocrystalline quartz and chlorite is characteristic of rhyolitic lavas.

Coniacian–Maastrichtian pelagic limestones overlie the basaltic-dacitic rocks of the Shahr-e-Babak volcanic sequence (Fig. 4e). Younger sediments record a hiatus during Paleocene to Early Eocene time, an unconformity overlain by Eocene conglomerate, which grades upwards into Nummulites-bearing limestones and then into coarse- to medium-grained sandstones. Ophiolitic cobbles are common in Eocene conglomerates (Dimitrijevic, Reference Dimitrijevic1973), demonstrating that the ophiolite was exposed and eroded at this time.

3.b.4. Balvard–Baft ophiolite

The Balvard–Baft ophiolite defines a 5–10 km wide WNW-trending belt, covering 800 km² (see Fig. A9 in online Appendix 1 at http://journals.cambridge.org/geo). This ophiolite extends NW towards Shahr-e-Babak and SE to the Dare–Pahn and Haji–Abad ophiolites (Fig. 2). The first report on the Balvard–Baft ophiolite was by Dimitrijevic (Reference Dimitrijevic1973) as a result of mapping of the Kerman region. Two types of basaltic pillow lavas and lava flows are recognized in the Baft and the Gogher (Balvard) regions (Arvin & Robinson, Reference Arvin and Robinson1994; Arvin & Shokri, Reference Arvin and Shokri1997): (1) tholeiites similar to N-MORB and (2) transitional tholeiites, geochemically intermediate between E-MORB and IAT, clearly produced by melting of a subduction-modified mantle.

The Balvard–Baft mantle sequence consists of harzburgite, minor lherzolite with diabasic dykes, and pockets of isotropic and pegmatitic gabbro. Harzburgite has porphyroclastic texture, with coarse, deformed orthopyroxene. Serpentinized olivine, clinopyroxene and dark brown spinel are other peridotite constituents. Plagioclase and clinopyroxene are the predominant cumulus phases in pegmatitic gabbros, with traces of olivine and spinel (< 3%). Plagioclase and clinopyroxene are the main constituents of the isotropic gabbros, with accessory magnetite and ilmenite.

Mafic to felsic rocks including pillow lavas, basaltic-andesitic-dacitic lava flows, and basaltic-andesitic-dacitic sills in pyroclastic rocks (Fig. 4g) are the Balvard–Baft ophiolite crustal units. Pillowed and massive lavas are porphyritic, with coarse-grained, euhedral to subhedral plagioclase and subhedral to anhedral clinopyroxene phenocrysts set in an altered glassy groundmass with plagioclase microlites. Basaltic lava flows are characterized by plagioclase and clinopyroxene whereas hornblende and plagioclase are dominant in andesites and dacites. Basaltic-andesitic and dacitic sills in pyroclastic rocks contain altered plagioclase laths set in a groundmass of altered glass and plagioclase microlites. Clinopyroxene phenocrysts are present, except in dacites, altered to uralite and chlorite especially around their margins. Some lavas are nearly aphyric with 1–2% plagioclase phenocrysts and pilotaxitic texture. Pyroclastic rocks and hyaloclastites rest unconformably over the basaltic lava flows (Fig. 4h). They are composed of volcanic breccias, agglomerates, tuff, tuffaceous sandstones and lutites, pillow cold breccias and andesitic hyaloclastites with basaltic-andesitic and pillow fragments. Volcaniclastic rocks are overlain by Turonian–Maastrichtian (93.5–65.5 Ma) pelagic limestones. The Balvard–Baft ophiolite is in fault or unconformable contact with Middle to Upper Eocene sedimentary-volcanic sequences related to the Urumieh–Dokhtar arc (Srdic et al. Reference Srdic, Dimitrijevic, Cvetic and Dimitrijevic1972; Mijalkovic, Cvetic & Dimitrijevic, Reference Mijalkovic, Cvetic and Dimitrijevic1972). These sediments consist of sandstone, marl and Nummulites-bearing limestone turbidites, with interbedded basaltic-andesitic lava flows above a basal conglomerate. The Early Eocene appears to have been a time of uplift and erosion of the ophiolite, as evidenced by ophiolitic clasts in Middle Eocene basal conglomerate.

4.a.1. Kermanshah ophiolite

The Kermanshah ophiolite magmatic succession is characterized by a sheeted dyke complex with mafic and felsic dykes, as well as by massive and pillowed lavas. To reconstruct the magmatic chemostratigraphy of this well-preserved ophiolite, we studied four sections along the Kherran to Sartakht road, near Sartakht village and near Siah-Pareh village.

Along the Kherran to Sartakht road there is a volcanic pile with sparsely phyric basaltic-andesites at the bottom grading upwards into porphyritic basalts with plagiogranitic veins and then into pillowed lavas (Fig. 3a and Fig. A10a in online Appendix 1 at http://journals.cambridge.org/geo). This sequence is capped by a thin basaltic flow. These lavas are basaltic with 49.6–52 wt% SiO₂. They have high FeO/MgO, and in the FeO/MgO v. SiO₂ diagram plot in the high-Fe tholeiitic field (Fig. 6). Mg no. (= 100 Mg/(Mg + Fe)) of these lavas varies from 43.4 to 66.4, indicating some are primitive. TiO₂ and Zr contents vary from ~ 1 to 1.9 wt% (Fig. 7) and 69 to 166 ppm, respectively. Sample KH09-24 has higher Zr content along with lower Mg no.

Figure 6.

FeO^t/MgO v. SiO₂ (volatile free, normalized to 100% total) for Zagros OB and IB magmatic rocks. Boundaries between tholeiitic and calc-alkaline suites (thin solid line) and between low-, medium- and high-Fe suites (thick, dashed lines) are from Miyashiro (Reference Miyashiro1974) and Arculus (Reference Arculus2003), respectively. For comparison compositional fields from the Kizildag ophiolite, Turkey (Dilek & Thy, Reference Dilek and Thy2009), Oman (Godard, Dautria & Perrin, Reference Godard, Dautria and Perrin2003) and IBM fore-arc lavas (Reagan et al. Reference Reagan, Ishizuka, Stern, Kelley, Ohara, Blichert-Toft, Bloomer, Cash, Fryer, Hanan, Hickey-Vargas, Ishii, Kimura, Peate, Rowe and Woods2010) are shown.

Figure 7.

Major element variations (TiO₂ v. MgO) of OB and IB mafic rocks and comparisons to Troodos upper and lower lavas (modified after Dilek & Thy, Reference Dilek and Thy2009). Troodos upper and lower lava fields are outlined by dashed and dotted lines, respectively.

On REE plots, samples KH09-17 (poorly phyric basaltic flow), KH09-19 (basaltic flow) and KH09-20 (pillow lava) have flat to slightly depleted REE patterns (La_N/Yb_N = 0.75–1.1) (Fig. 8a). These samples show similar REE patterns except for slight Eu enrichment in KH09-17 and KH09-19, with REE contents similar to N-MORB (e.g. La = 2.2–4.1 ppm, Yb = 2.1–2.6 ppm versus N-MORB = 2.5 ppm La, 3.05 ppm Yb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989). Sample KH09-24 is LREE enriched (La_N/Yb_N = 2.4) similar to calc-alkaline lavas (Fig. 8a). The N-MORB-normalized trace element patterns for Kermanshah basaltic rocks show strong depletion in Nb–Ta relative to light REEs (LREEs) (Nb/La = 0.5–0.9 × N-MORB) (Fig. 8b). These basalts are enriched in large-ion-lithophile elements (LILEs) (e.g. Rb, Ba, U, K, Pb) relative to LREEs. All basaltic rocks in this sequence are IAT except KH09-24 which displays a calc-alkaline affinity. IAT and calc-alkaline lavas interfinger in this sequence.

Figure 8.

Chondrite-normalized rare earth element patterns (chondrite abundances are from McDonough & Sun, Reference McDonough and Sun1995) and normal mid-ocean ridge basalt (N-MORB)-normalized multi-element patterns (N-MORB concentrations are from Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989) for rock units of outer belt ophiolites. (a, b) Kermanshah ophiolite; (c, d) Neyriz ophiolite; and (e, f) Haji–Abad ophiolite.

A sheeted dyke complex near Kherran village contains older diabasic dykes intruded by younger andesitic-dacitic-rhyolitic dykes (Fig. 3b, c and Fig. A10 in online Appendix 1 at http://journals.cambridge.org/geo). All mafic dyke samples (KH09-26, KH09-36 and KH09-37) are basalts and basaltic-andesites, with 51 to 54 wt% SiO₂. These lavas have lower FeO/MgO and plot in the medium-Fe tholeiitic to low-Fe calc-alkaline fields (Fig. 6). They are fractionated, with low Mg no. (44 to 53.9) and elevated TiO₂ (1.7 to 2.8 wt%) (Fig. 7) and Zr (212 to 316 ppm). These mafic lavas are LREE enriched (Fig. 8a) with La_N/Yb_N ranging from 2.8 to 3.3. Depletion in Nb–Ta and enrichment in Rb, Ba, Th, U, K and Pb relative to N-MORB (e.g. Nb/La = 0.55–0.7 × N-MORB and Th/La = 5.6–6.3 × N-MORB) are characteristic of these mafic dykes (Fig. 8b). Felsic dykes have higher SiO₂ (53–56 wt%) and Zr contents (426–474 ppm). They contain 5.6–5.9 wt% Na₂ O, which may be magmatic because alteration is not severe, as shown by low loss on ignition (LOI: 0.4–0.8 wt%).

Kherran dykes show REE patterns that are concave upwards from La to Eu (Fig. 8a), with a slight increase from heavy REEs (HREEs) to middle REEs (MREEs) (Dy_N/Yb_N = 1.1–1.3 × chondrite) and low La_N/Sm_N (0.7–0.96) but with La_N/Yb_N = 0.98–2.2. These patterns may be attributed to crystal fractionation of basaltic melt to form felsic magmas. Like the mafic rocks, felsic dykes show slight negative Nb–Ta (and Ti) and positive Rb, Ba, Th, K, U and Pb anomalies relative to N-MORB (e.g. Nb/La = 0.88 × N-MORB, except KH09-31 with Nb/La = 2.5 × N-MORB and Th/La = 28.5–7.3 × N-MORB) (Fig. 8b). In this section, earlier mafic dykes are calc-alkaline grading into later felsic dykes that probably are fractionated arc tholeiites or products of amphibolite melting.

A well-preserved pillow lava sequence near Siah-Pareh village is > 100 m thick (Fig. A10c in online Appendix 1 at http://journals.cambridge.org/geo and Fig. 3d). To characterize the melt evolution with time, we sampled from the bottom to the top of this pillow sequence. These are fractionated basalts, with relatively constant SiO₂ (~ 52 wt%) and low Mg no. (44–47). These lavas have lower FeO/MgO and are similar to low-Fe calc-alkaline lavas (Fig. 6). They are characterized by high TiO₂ (~ 1.8 wt%) and Zr (~ 200 ppm), similar to lower Troodos lavas (Fig. 7). REE patterns (Fig. 8a) do not change systematically from the bottom to the top of the pillow sequence. The lavas have similar REE patterns, enriched in LREEs (La_N/Yb_N = 2.2–2.9) and LILEs (e.g. Th/La = 28.5–7.3 × N-MORB), and depleted in Nb–Ta (e.g. Nb/La = 0.5–0.6 × N-MORB), typical features of calc-alkaline rocks.

A sheeted dyke complex overlain by pillow lavas is found between Sartakht and Siah-Pareh villages (see Fig. A10d in online Appendix 1 at http://journals.cambridge.org/geo). These lavas are fractionated basalts and basaltic-andesites, with variable SiO₂ (49–54 wt%), Mg no. (31–59) and calc-alkaline signature (Fig. 6). They vary from more primitive (KH09-75 and KH09-79 with MgO = 6.41 wt%, TiO₂ = 1.22–1.4 wt% and Zr = 125–138 ppm, respectively) to more evolved (KH09-82 and KH09-76 with MgO = 2.89–3.34 wt%, TiO₂ = 2.46–2.51 wt% and Zr = 230–255 ppm, respectively) (Fig. 7). All lavas are LREE enriched, with La_N/Yb_N between 3 and 3.6 (Fig. 8a). Depletion in Nb–Ta (e.g. Nb/La = 0.5–0.7 × N-MORB) and enrichment in LILEs (e.g. Th/La = 5.3–6.5 × N-MORB), similar to calc-alkaline series, characterizes these lavas.

Kermanshah lavas display both tholeiitic and calc-alkaline trends in terms of FeO/MgO v. SiO₂ (Fig. 6), with dispersion in FeO/MgO and SiO₂ contents. Such dispersion along with the presence of tholeiitic and calc-alkaline lavas was considered by Miyashiro (Reference Miyashiro1973) to be typical of arc magmas. The Kermanshah lavas have high TiO₂ contents with a primary to evolved nature, evidenced by their MgO content (Fig. 7). Kermanshah lavas have high Ti/V, ranging from 35 in arc tholeiites to 104 in calc-alkaline lavas. In spite of LILE enrichments and Nb–Ta depletions, characteristics indicating arc-like compositions, these ratios fall into the MORB and within-plate fields of Shervais (Reference Shervais1982) (Fig. 9a).

Figure 9.

Ti v. V diagram (after Shervais, Reference Shervais1982) for Zagros outer belt (a) and inner belt (b) ophiolites. For comparison, fields for the V1 (lower, Geotimes unit) and V2 (upper, Lasail unit) lavas of Oman ophiolite (data from Alabaster, Pearce & Malpas, Reference Alabaster, Pearce and Malpas1982) and for Mariana fore-arc basalts and boninites (Reagan et al. Reference Reagan, Ishizuka, Stern, Kelley, Ohara, Blichert-Toft, Bloomer, Cash, Fryer, Hanan, Hickey-Vargas, Ishii, Kimura, Peate, Rowe and Woods2010) are shown.

Reconstruction of Kermanshah ophiolitic lava chemostratigraphy indicates that lava compositions do not show major changes in the sections described above, only interfingering of IAT and calc-alkaline lavas in the Kherran to Sartakht road section.

4.a.2. Neyriz ophiolite

The volcanic and hypabyssal sequence of the Neyriz ophiolite is represented by mafic and felsic dykes in a sheeted dyke complex, massive and pillowed lavas, and dykes in mantle peridotite. Despite several studies on the Neyriz ophiolite (e.g. Babaie et al. Reference Babaie, Babaei, Ghazi and Arvin2006; M. R. Jannessary, unpub. Ph.D. thesis, l'Univ. de Louis Pasteur, France, 2003), we know little about its chemostratigraphical evolution, probably because the crustal sequence is highly faulted. Here we try to combine our field observations plus geochemical data from M. R. Jannessary (unpub. Ph.D. thesis, l'Univ. de Louis Pasteur, France, 2003). We selected three volcanic sequences for closer scrutiny: (1) isolated diabasic to andesitic dykes injected into mantle harzburgites (NJ755, NJ633, NJ294, NJ296, NJ217), (2) Dowlat–Abad pillowed and massive lavas with intercalated pelagic sediments (NJ223, NJ5, NJ303, NJ222) (Fig. 3e and Fig. A10e in online Appendix 1 at http://journals.cambridge.org/geo) and (3) Tale–Afshari sheeted dyke/lava sequence with felsic and mafic dykes (NJ591, NJ594, NJ596, NJ609, NJ603, NJ601) (Fig. 3f and Fig. A10f in online Appendix 1 at http://journals.cambridge.org/geo). Unfortunately we cannot separately discuss the lava and dyke geochemistry because these are not distinguished.

Dykes intruding mantle rocks vary from basaltic (diabasic) to andesitic with 45 to 54 wt% SiO₂ (Fig. 5a). These dykes are mostly tholeiitic with high FeO/MgO (Fig. 6). These dykes display variable enrichment in TiO₂ (0.3–2.2 wt%) and Zr (10–92 ppm). In the TiO₂ v. MgO diagram, TiO₂-rich dykes resemble lower lavas of Troodos while TiO₂-poor dykes show similarity to Troodos upper lavas (Fig. 7). They are geochemically divided into (1) IAT-like dykes that are enriched in bulk REEs (NJ633 and NJ755; La = 3.3–4.8 ppm, Yb = 3.2–4.3 ppm versus N-MORB = 2.5 ppm La, 3.05 ppm Yb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989) but are LREE depleted (La_N/Yb_N = 0.8), have modest negative Nb anomalies (Nb/La = 0.8 × N-MORB) and are enriched in LILEs relative to LREEs (e.g. Th/La = 1.7–1.8 × N-MORB) (Fig. 8c, d); and (2) boninitic dykes, which are depleted in bulk REEs (NJ294, NJ296, NJ217) with La = 0.7–1 ppm and Yb = 1–1.8 ppm (versus N-MORB = 2.5 ppm La, 3.05 ppm Yb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989), are LREE depleted (La_N/Yb_N = 0.3–0.7), have negative Nb anomalies (Nb/La = 0.6–0.8 × N-MORB) and are enriched in positive LILEs relative to LREEs (e.g. Th/La = 3–4.6 × N-MORB) (Fig. 8c, d). Boninitic dykes also have lower Zr and TiO₂ contents.

Dowlat–Abad pillow lavas (Fig. 3e and Fig. A10e in online Appendix 1 at http://journals.cambridge.org/geo) are andesitic to dacitic with variable SiO₂ (56–68 wt%; Fig. 5a) and Zr contents (67–106 ppm). They have high FeO/MgO (Fig. 6) and moderate TiO₂ (1.4–1.7 wt%) (Fig. 7a). They have approximately flat REE patterns (Fig. 8c) with La_N/Yb_N = 0.7–1.3, Nb depletion (Nb/La = 0.5–0.8 × N-MORB) and LILE enrichment (e.g. Ba/La = 1.2–8.9 × N-MORB), transitional between N-MORB and IAT (similar to fore-arc basalts).

Tale-Afshari lavas and dykes include both more- and less-evolved samples (M. R. Jannessary, unpub. Ph.D. thesis, l'Univ. de Louis Pasteur, France, 2003). Less-evolved lavas are characterized by low SiO₂ (50–55 wt%), Zr (20–65 ppm) and higher MgO (2.4–6.4 wt%). Lower MgO (0.5–2.5 wt%) and higher Zr (48–205 ppm) and SiO₂ (63–70 wt%) contents of more-evolved samples confirm these represent fractionated magmas. They are mostly tholeiitic (Fig. 6) and similar to lower lavas of Troodos (Fig. 7). More-evolved types have higher bulk REE concentrations (e.g. La = 5.2–6.6 ppm, Yb = 4.8–7.4 ppm versus N-MORB = 2.5 ppm La, 3.05 ppm Yb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989) with LREE depletion (La_N/Yb_N = 0.6–0.8) and negative Nb anomalies (Nb/La = 0.4–0.5 × N-MORB). These types of lavas show negative Eu anomalies (Eu/Eu* = 0.7–0.8) indicating plagioclase differentiation. The less-evolved types do not show negative Eu anomalies and are characterized by lower bulk REE contents (e.g. La = 1.6–2.3 ppm, Yb = 2.3–3.1 ppm v. N-MORB = 2.5 ppm La, 3.05 ppm Yb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989). These types also show LREE depletion (La_N/Yb_N = 0.5–0.6) and significant Nb anomalies (Nb/La = 0.5–0.8 × N-MORB). Both Tale–Afshari lava types have an IAT signature, indicating formation in a suprasubduction zone environment. Most Neyriz lavas are medium- to high-Fe tholeiitic (Fig. 6), characterized by low MgO and high TiO₂ contents resembling Troodos lower lavas (Fig. 7). Some boninitic samples, with lower FeO/MgO and TiO₂ abundances, are similar to Troodos upper lavas (Fig. 7). On a Ti v. V diagram (Shervais, Reference Shervais1982) (Fig. 9a), some plot as IAT while others have slightly higher TiO₂ content, transitional between MORB and IAT.

4.a.3 Haji–Abad ophiolite

Haji–Abad ophiolitic lavas vary in composition from tholeiitic to calc-alkalic (Fig. 6) and from moderately high to very low TiO₂ contents. Three volcanic sequences are distinguished: (1) older E-MORB-type pillow lavas, (2) calc-alkaline volcanic rocks and (3) younger boninitic lavas. E-MORB type pillow lavas (HG10-21, HG10-25 & HG10-26) are found near the MZT, especially near Sheikh-Ali village (see Fig. A4 in online Appendix 1 at http://journals.cambridge.org/geo). These older, E-MORB-type lavas are highly altered with relatively high LOI contents (7.9–10.6 wt%) and variably fractionated Mg no. (47–53). They are high-Fe tholeiitic (Fig. 6) similar to Troodos lower lavas (Fig. 7). These lavas have moderately high TiO₂ (1.5–1.8 wt%) (Fig. 7) and plot in the MORB field on a Ti v. V diagram (Shervais, Reference Shervais1982), similar to V1 Oman lavas (Fig. 9a), thought to be the first lavas to erupt. Haji–Abad E-MORB lavas are LREE enriched (La_N/Yb_N = 4.3–7.2) (Fig. 8e) and have positive Nb anomalies (Nb/La = 1.4–1.7 × N-MORB). They are enriched in LILEs (e.g. Th/La = 2.5–3.1 × N-MORB) (Fig. 8f).

Calc-alkaline lavas are massive or pillowed and are associated with pelagic limestone layers in the Chale–Mort to Haji–Abad tectonic mélange; they are also stratigraphically overlain by pelagic limestones (see Fig. A10g in online Appendix 1 at http://journals.cambridge.org/geo). Sample HG10-17 is from a lava flow on top of the turbidite sequence. These lavas are acidic andesite to dacite in composition with SiO₂ and TiO₂ ranging from 60 to 69 wt% (except sample HG10-14 that is characterized by SiO₂ leaching during alteration and a high content of LOI; 10.8 wt%) and 0.47 to 0.95 wt%, respectively. They are more-evolved lavas, with Mg no. indicating significant fractionation, from 33 to 43. In the FeO/MgO against SiO₂ diagram, these lavas plot in the tholeiitic field (Fig. 6) similar to Troodos lower lavas (Fig. 7). These lavas are slightly enriched in LREEs (La_N/Yb_N = 1.6–2.2) and LILEs (e.g. Th/La = 2.6–3.2 × N-MORB and Pb/La = 1.1–5.7 × N-MORB). They are strongly depleted in Nb (Nb/La = 0.3–0.8 × N-MORB) and TiO₂ (0.5–0.9 wt%), as expected for subduction-related igneous rocks.

Late boninitic magmatism is represented by pillowed and massive lavas. They are basaltic to basaltic andesite in composition with variable SiO₂ (41–54 wt%) and Mg no. (43.8–76.9). The low SiO₂ content of some lavas may partly reflect alteration, as indicated by high LOI (4.2–6.2 wt%). These lavas have very low Zr (4.7–6.1 ppm) and TiO₂ (0.3–0.4 wt%) contents and FeO/MgO and are similar to Troodos upper lavas (Figs 6, 7). Their low Ti and V contents plot in the boninitic field of the Shervais (Reference Shervais1982) discrimination diagram (Fig. 9a). Haji–Abad boninitic lavas also are highly depleted in bulk REEs (e.g. La = 0.1–0.3 ppm, Yb = 0.9–1.2 ppm v. N-MORB = 2.5 ppm La, 3.05 ppm Yb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989). They are strongly LREE depleted (La_N/Yb_N = 0.1–0.2) (Fig. 8e), with large negative Nb anomalies (e.g. Nb/Th ~ 0.1 × N-MORB) and are strongly enriched in LILEs relative to LREEs (e.g. Th/La = 13.9–41.7 × N-MORB). These boninites are similar to the Ca-boninites of Falloon & Crawford (Reference Falloon and Crawford1991). A late microgabbroic dyke injected into the Haji–Abad mantle sequence (HG10-30) is compositionally similar to boninitic lavas. The dyke has low contents of bulk REEs (e.g. La = 0.2 ppm and Yb = 0.5 ppm), TiO₂ (0.2 wt%) and Zr (2.5 ppm). This dyke is very depleted in LREEs (La_N/Yb_N = 0.3) and Nb (Nb/La = 0.5 × N-MORB), similar to boninites. This may be a feeder dyke for the boninitic lavas.

We tentatively conclude that Haji–Abad magmatism evolved from early E-MORB to boninitic.

4.b.1. Nain ophiolite

Crustal rock units in the Nain ophiolite consist of massive and pillowed lavas, a sheeted dyke complex and amphibole gabbros, which also serve as a root zone for the sheeted dyke complex. Diabasic-gabbroic-noritic dykes and isotropic gabbro lenses are widespread within the Nain mantle sequence. To better constrain the chemostratigraphic evolution of the Nain ophiolite, we sampled two sequences where age relationships are clear: (1) a sheeted dyke complex with overlying pillow lavas and underlying gabbros and plagiogranites (see Fig. A11a in online Appendix 1 at http://journals.cambridge.org/geo), and (2) intrusions in mantle peridotite, including early rodingitized diabasic-gabbroic dykes/sills and late chloritized diabasic dykes (see Fig. A11b in online Appendix 1 at http://journals.cambridge.org/geo). The sheeted dyke complex includes earlier diabasic and later dacitic-rhyolitic-noritic dykes. In the root zone of this complex, the diabasic dykes intrude gabbros, microgabbros, amphibole gabbros and plagiogranite (see Fig. A11a in online Appendix 1 at http://journals.cambridge.org/geo). Dykes intrude each other at higher levels. A pillow lava sequence overlies the dyke complex and is covered by pelagic sediments.

Nain ophiolitic dykes are classified into earlier IAT and later boninitic dykes. The FeO/MgO of these dykes mostly distribute in medium-Fe tholeiitic to low-Fe calc-alkaline domains (Fig. 6). These dykes have variable and low contents of TiO₂ (0.2–0.8 wt%) and Zr (17.5–32.5 ppm). Their low TiO₂ content is similar to Troodos low-Ti upper lavas (Fig. 7). One early IAT dyke (BAH-14) is LREE depleted (La_N/Yb_N = 0.54) (Fig. 10a). This dyke contains less REE than N-MORB (e.g. La = 1.56 ppm, Yb = 2.07 ppm versus N-MORB = 2.5 ppm La, 3.05 ppm Yb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989). It is highly depleted in Nb–Ta (e.g. Nb/La = 0.31 × N-MORB) and enriched in LILEs relative to LREEs (e.g. Th/La = 2.8 × N-MORB) (Fig. 10b). Later boninitic-IAT and boninitic dykes are represented by samples BS05-16 and BS05-13, respectively. BS05-16 shows a LREE-depleted pattern (La_N/Yb_N = 0.45) whereas BS05-13 has a U-shaped REE pattern (Fig. 10a, b), with La_N/Yb_N = 1.05, typical of boninites (Crawford, Falloon & Green, Reference Crawford, Falloon, Green and Crawford1989). These dykes are depleted in REEs relative to N-MORB (e.g. La = 1.24–0.85 ppm, Yb = 0.85–1.36 ppm v. N-MORB = 2.5 ppm La, 3.05 ppm Yb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989). A negative Nb anomaly is common for these dykes (e.g. Nb/La = 0.3–0.9 × N-MORB). Late andesitic-dacitic dykes (BS05-12, BS05-8 A) intrude diabases in the Nain sheeted dyke complex. These dykes have 55–64 wt% SiO₂ and 0.5–0.7 wt% TiO₂, with low Zr contents (26–51 ppm). These plot in the calc-alkaline field on the FeO/MgO versus SiO₂ diagram (Fig. 6). Felsic dykes are characterized by depleted LREEs (La_N/Yb_N = 0.5) and Nb–Ta (e.g. Nb/La = 0.5–0.96 × N-MORB) (Fig. 10a, b), similar to IAT trace element patterns. Sample BS05-8 A shows a negative Eu anomaly, suggesting that this was a highly fractionated melt in equilibrium with cumulate or residual plagioclase.

Figure 10.

Chondrite-normalized rare earth element patterns (chondrite abundances are from McDonough & Sun, Reference McDonough and Sun1995) and normal mid-ocean ridge basalt (N-MORB)-normalized multi-element patterns (N-MORB concentrations are from Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989) for rock units of inner belt ophiolites. (a, b) Nain ophiolite; (c, d) Dehshir ophiolite; (e, f) Shahr-e-Babak ophiolite; and (g, h) Balvard–Baft ophiolite.

Pillowed tholeiitic lava (BAH-35) found above the sheeted dyke sequence has higher TiO₂ (0.9 wt%) and Zr (61 ppm) relative to dykes. This lava has a flat REE pattern (La_N/Yb_N = 0.9) and is enriched in LILEs relative to LREEs (e.g. Ba/La = 7.7 × N-MORB). Th/La is higher than that of N-MORB (Th/La = 2.25 × N-MORB), and Ba is even more enriched (Ba/Th = 3.4 × N-MORB). Nb–Ta is depleted relative to K and U (e.g. U/Nb = 2.9 × N-MORB), although Nb content of the Nain pillow lava is slightly higher than that of N-MORB (Nb = 2.63 versus N-MORB = 2.33 ppm Nb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989).

Geochemically, most gabbros below the Nain sheeted dyke complex are LREE-depleted IAT (La_N/Yb_N = 0.77–0.16), except samples BAH-12 and BS05-11 which are boninitic (Fig. 10a, b). Most gabbros are depleted in Nb compared to LREEs (Nb/La = 0.23–1.6 × N-MORB) (Fig. 10b). BAH-12 and BS05-11 have very low REE contents (e.g. La = 0.16–0.34 ppm, Yb = 0.72–0.73 ppm versus N-MORB = 2.5 ppm La, 3.05 ppm Yb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989), indicating derivation from highly depleted mantle.

Dykes and sills intruding mantle peridotites, including a gabbroic dyke (BSP-3) and diabasic dykes (BSU-10 & BSU-11), are variably altered, from a rodingitized dyke with high LOI (9.5 wt%) to diabasic dykes with lower LOI (2.1–2.6 wt%). They are characterized by low TiO₂ (0.5–0.8 wt%) and Zr (21–62 ppm). These dykes are LREE-depleted (Fig. 10a) (La_N/Yb_N = 0.9–0.4) with negative Nb–Ta (Nb/La = 0.3–0.2 × N-MORB) and positive LILE anomalies (U/La = 2.9–2.8 × N-MORB). The gabbroic dyke (BSP-3) is more differentiated (e.g. La = 2.73 ppm versus N-MORB = 2.5 ppm La; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989) and the diabasic dyke BSU-10 is boninitic with low REE contents (e.g. La = 0.8 ppm versus N-MORB = 2.5 ppm La; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989).

Most Nain lavas scatter in the FeO/MgO v. SiO₂ diagram (Fig. 6). All Nain ophiolite rock units are depleted in immobile Nb and HREEs (Fig. 10b), demonstrating a subduction-related source for genesis of these magmas. On a Ti v. V diagram (Shervais, Reference Shervais1982), lavas show IAT or boninitic affinities (Fig. 9b) and otherwise resemble Troodos upper pillow lavas (Fig. 7). Injection of late boninitic and noritic dykes into early tholeiitic dykes indicate that Nain magmas evolved from early IAT into late boninites as the ophiolite formed. A similar conclusion is reached for dykes intruding mantle peridotites, where late boninitic and non-altered noritic dykes are found.

4.b.2. Dehshir ophiolite

Detailed geochemical data and interpretations were presented by Shafaii Moghadam, Stern & Rahgoshay (Reference Shafaii Moghadam, Stern and Rahgoshay2010); here we focus on the chemostratigraphy of ophiolite magmatic units. Fine-grained isotropic gabbros, pillow basalts, basaltic lava flows and basaltic-andesitic-dacitic dykes (in a sheeted dyke complex and intruding amphibole gabbros) are the magmatic rocks of the Dehshir ophiolite. These magmatic rocks belong to both the calc-alkaline and tholeiitic series (Fig. 6). Some samples are similar to Troodos lower lavas, with higher TiO₂ contents, while others resemble Troodos upper lavas (Fig. 7).

Pillow lavas above the sheeted dyke complex (AZ06-32, DAR05-6) (Fig. 4c) and harzburgites (A06-2, A06-3) in the Ardan region (see Fig. A11d in online Appendix 1 at http://journals.cambridge.org/geo) show either flat REE patterns (La_N/Yb_N = 1.1–1.2) or are LREE enriched (La_N/Yb_N = 2.7–3.3) typical of IAT and calc-alkaline series, respectively (Fig. 10c). On an N-MORB-normalized trace element diagram, these lavas are depleted in Nb (Nb/La ~ 0.2–0.7 × N-MORB) and enriched in Pb, U, Ba and Th (e.g. Th/La ~ 1–3 × N-MORB) (Fig. 10d).

The sheeted dyke complex includes early basalts and late dacitic dykes (see Fig. A11c in online Appendix 1 at http://journals.cambridge.org/geo). An early basaltic dyke (sample AZ06-38) in the sheeted dyke complex has a nearly flat REE pattern (Fig. 10c) with La_N/Yb_N = 0.8. It shows no high-field-strength element (HFSE) depletion (Nb/La = 1.1 × N-MORB) and geochemically is similar to N-MORB. Late dacites in the sheeted dyke complex have nearly flat REE patterns (La_N/Yb_N = 1.2–1.3). Relative to N-MORB, these rocks are depleted in Nb, Ta, P and Ti, whereas U, Th and Pb show positive anomalies (Fig. 10d). Felsic dykes show trace element similarities with low-K tholeiitic or calc-alkaline rock series. Dacitic dykes are distinguished by very low Sr/Y and La_N/Yb_N (3.9–10 and 1.2–1.3, respectively), typical of low-pressure basalt fractionates or amphibolite melts (Shafaii Moghadam, Stern & Rahgoshay, Reference Shafaii Moghadam, Stern and Rahgoshay2010).

Isotropic gabbros beneath the sheeted dyke complex (samples D06-3 & DZ05-1 H) (Fig. 4c) have flat to LREE-depleted patterns (La_N/Yb_N = 1.7–0.4) with strong Nb depletion (Nb/La = 0.2–0.5 × N-MORB). An andesitic dyke (DZ05-1D) intruding gabbro has low REE contents relative to N-MORB (e.g. La = 0.8 ppm and Yb = 1.5 ppm v. N-MORB = 2.5 ppm La, 3.05 ppm Yb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989), with LREE and Nb depletion (La_N/Yb_N = 0.4; Nb/La = 0.4 × N-MORB), similar to boninite. On a Ti v. V diagram (Shervais, Reference Shervais1982), Dehshir lavas show MORB to boninitic affinities (Fig. 9b).

A diabasic dyke in mantle harzburgite (AZ06-29; see Fig. A11d in online Appendix 1 at http://journals.cambridge.org/geo) is slightly LREE enriched (La_N/Yb_N = 1.6) but is strongly depleted in Nb and Ta (e.g. Nb/La ~ 0.3 × N-MORB), typical of calc-alkaline series. Dyke sample A06–1 is compositionally similar to overlying pillow lavas. Another diabasic dyke (AZ06-29, Fig. 10c, d) is depleted in total REEs (La = 0.6 ppm, Yb = 0.8 ppm versus N-MORB = 2.5 ppm La, 3.05 ppm Yb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989), LREE-depleted (La_N/Yb_N = 0.5) and is strongly depleted in Nb (Nb/La = 0.5 × N-MORB).

Although disruption of rock units during and after ophiolite emplacement prohibits reconstructing Dehshir ophiolitic lava chemostratigraphy in detail, the data of Shafaii Moghadam, Stern & Rahgoshay (Reference Shafaii Moghadam, Stern and Rahgoshay2010) indicate that basalt lava compositions vary from MORB and IAT to calc-alkaline and boninitic with time (see Fig. A11c, d in online Appendix 1 at http://journals.cambridge.org/geo). For example, the base of pillow lavas (see Fig. A11c in online Appendix 1 at http://journals.cambridge.org/geo) is IAT (sample AZ06–32) and is intruded by basaltic-dacitic dyke swarms. Early basaltic dykes (sample AZ06–38) are N-MORB and are intruded by late dacitic dykes with a suprasubduction zone chemical signature. We saw no evidence in the field for a break between the MORB/IAT (lower) and the upper (IAT/boninite) sequences in the form of an unconformity or intervening sedimentary sequence.

4.b.3. Shahr-e-Babak ophiolite

Basaltic to rhyolitic lava sheets interbedded with Upper Cretaceous pelagic sediments (limestones, radiolarites, marly limestones) (Fig. 4f and Fig. A11f in online Appendix 1 at http://journals.cambridge.org/geo) are the main components of the Shahr-e-Babak ophiolite crustal sequence. Lavas are basaltic, andesitic, dacitic and rhyolitic together with minor pyroclastic rocks. Rhyolitic dykes and sills cross-cut this rock assemblage. To constrain the geochemical signatures of this sequence, we selected interbedded mafic (R06-9, R06-45, R05-6, R06-32 and R06-24), andesitic (R06-41) and dacitic samples (R06-39). A rhyolitic dyke (R06-26) injected into the lavas is also discussed (Fig. 4e and Fig. A11f in online Appendix 1 at http://journals.cambridge.org/geo). Interbedded lavas have SiO₂ and Mg no. ranging from 47 to 70 wt% and 62 to 27, respectively. The rhyolitic dyke is more evolved with 74 wt% SiO₂ and a Mg no. of 22. These lavas mostly have higher FeO/MgO and are mildly tholeiitic (Fig. 6) with some calc-alkaline samples. Their variable TiO₂ contents overlap with both lower and upper Troodos lavas (Fig. 7). These lavas display two REE patterns (Fig. 10e): (1) slightly to highly LREE enriched and (2) LREE depleted. LREE-enriched samples show La_N/Yb_N = 1.3 for dacitic lava (sample R06-39) and La_N/Yb_N = 6.1–7.1 for some mafic lavas (samples R05-6 and R06-45). HFSE depletion and LILE enrichment relative to LREEs is typical for these lavas (e.g. Nb/La = 0.1–0.3 × N-MORB, Th/La ~ 2.5–7.3 × N-MORB and U/La ~ 2.4–3.9 × N-MORB). Some mafic lavas show calc-alkaline to shoshonitic affinities. LREE-depleted samples have La_N/Yb_N = 0.4–0.9 and are depleted in Nb–Ta relative to LREEs (Nb/La ~ 0.3 × N-MORB), similar to IAT. Samples R06-32 and R06-9 are exceptional, with low concentrations of REEs (e.g. La = 0.7–1.1 ppm, Yb = 1.5–1.2 ppm versus N-MORB = 2.5 ppm La, 3.05 ppm Yb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989) similar to boninites. A rhyolitic dyke has a nearly flat REE pattern, La_N/Yb_N = 1.1 (Fig. 10e), negative Eu anomaly, depletion in Nb (Nb/La ~ 0.3 × N-MORB) and LILE enrichment (Th/La ~ 2.5 × N-MORB), confirming formation as a low-pressure fractionate of IAT magma or amphibolite melt.

Based on field observations, it seems that calc-alkaline-shoshonitic lavas are younger than tholeiites. Lavas are interbedded with Upper Cretaceous pelagic sediments. Upper Cretaceous calc-alkaline-shoshonitic lavas are sometimes confused with Eocene shoshonitic basaltic-dacitic lavas, but some features distinguish them: (1) Upper Cretaceous ones are interbedded with Upper Cretaceous pelagic sediments with no evidence of injection into pelagic limestones, and (2) dacitic-rhyolitic lavas associated with ophiolites are tholeiitic compared to Eocene calc-alkaline dacites.

Shahr-e-Babak ophiolite pillow lavas (see Fig. A11e in online Appendix 1 at http://journals.cambridge.org/geo) occur as isolated patches in fault contact with massive lava flows. Massive and pillowed lavas are variably evolved (Fig. 5) with SiO₂ and Mg no. ranging from 50 to 74 wt% and 31 to 54, respectively. These lavas are tholeiitic (Fig. 6) and resemble Troodos lower lavas (Fig. 7) with slightly higher TiO₂ content (~ 0.7 wt%). A pillow lava sample (R06-4) is slightly LREE-depleted (La_N/Yb_N = 0.9) with negative Nb anomaly relative to LREEs (Nb/La ~ 0.3 × N-MORB) resembling IAT (Fig. 10e, f). Overlying basaltic to dacitic lava flows, as well as interbedded rock units discussed above, are classified as: (1) those with flat REE patterns (La_N/Yb_N = 0.9–1.3) and Nb depletions (Nb/La ~ 0.2–0.3 × N-MORB), similar to IAT, and (2) those with LREE-enriched patterns (La_N/Yb_N = 2.3–6.5) and strong Nb depletions (Nb/La ~ 0.1–0.5 × N-MORB) resembling calc-alkaline to shoshonitic lavas. Both types are overlain by Upper Cretaceous pelagic limestones.

Nb depletion is especially conspicuous for Shahr-e-Babak lavas compared with other inner and outer belt ophiolitic lavas; calc-alkaline rocks have more Nb than tholeiitic-boninitic lavas (Fig. 10f). On a Ti v. V diagram (Shervais, Reference Shervais1982), the Shahr-e-Babak lavas scatter in the fields of boninite to MORB (Fig. 9b); felsic lavas have very low V and Ti concentrations.

Although disruption and faulting of the Shahr-e-Babak ophiolite prohibits chemostratigraphic reconstruction of lava stratigraphy, our field observations for individual sections suggest that lava compositions changed from IAT/boninite into calc-alkaline-shoshonitic with time.

4.b.4. Balvard–Baft ophiolite

Crustal rock units in the Balvard–Baft ophiolite consist of massive and pillowed lavas, overlain by pyroclastic rocks. Basaltic to dacitic sills are common within the pyroclastic rocks (Fig. 4g and Fig. A11h in online Appendix 1 at http://journals.cambridge.org/geo). Upper Cretaceous pelagic limestones rest unconformably on the pyroclastic rocks (Fig. 4h). Isotropic gabbro lenses are common within the Balvard–Baft mantle sequence. To better constrain the chemostratigraphic evolution of the Balvard–Baft ophiolite, we studied two sequences: (1) an isotropic gabbro lens including early diabasic and late gabbroic dykes NNW of Baft (see Fig. A11g in online Appendix 1 at http://journals.cambridge.org/geo), and (2) a volcanic sequence (Cheshmeh–Baghal sequence) grading upwards into pyroclastic rocks and capped by Upper Cretaceous pelagic limestones (Fig. 4h and Fig. A11h in online Appendix 1 at http://journals.cambridge.org/geo). Mafic samples of the Balvard–Baft ophiolite have 40 wt% (most altered basaltic sample) to 54 wt% SiO₂ and 23 to 72 Mg no. They are characterized by medium-Fe, mildly tholeiitic to calc-alkaline signatures (Fig. 6). Most have low TiO₂ content and plot in upper lava field of the Troodos ophiolite (Fig. 7).

An isotropic gabbro sample (BT05-5) is LREE enriched (La_N/Yb_N = 2.2) (Fig. 10g) with slight Nb depletion relative to LREEs (Nb/La ~ 0.8 × N-MORB) (Fig. 10h) similar to T-MORB. Early diabasic dykes (sample BT05-2 A) cross-cut isotropic gabbros and are enriched in LREEs (La_N/Yb_N = 2.2) and LILEs (e.g. Th/La ~ 3.6 × N-MORB) without a negative Nb anomaly (Nb/La ~ 1.1 × N-MORB). These dykes are compositionally transitional between transitional mid-ocean ridge basalts (T-MORB) and calc-alkaline lavas. Late gabbroic dykes (BT05-3 & BT05-6) also are enriched in LREEs (La_N/Yb_N = 1.6–1.7) and Th (Th/La ~ 3.1 × N-MORB) and are somewhat depleted in Nb (Nb/La ~ 0.7 × N-MORB), similar to calc-alkaline series. This suggests that magmas evolved from MORB to calc-alkaline with time. Other isotropic gabbros in the Balvard–Baft mantle sequence (e.g. BT06-33) show calc-alkaline affinities with LREE enrichment (La_N/Yb_N = 1.5) and Th (Th/La ~ 3.2 × N-MORB) and Nb depletion (Nb/La ~ 0.3 × N-MORB) (Fig. 10g, h).

E-MORB-type pillow lavas were first reported by Arvin & Robinson (Reference Arvin and Robinson1994) in the Balvard–Baft ophiolite. Pillow lavas at the base of the ophiolite volcanic sequence are LREE enriched (La_N/Yb_N ~ 5–6), lack Nb depletion (Nb/La ~ 1.4 × N-MORB) and are similar to E-MORB. Overlying massive lavas (samples BT06-13 & BT06-15) are LREE and Nb depleted (La_N/Yb_N ~ 0.7–0.8; Nb/La ~ 0.2 × N-MORB) (Fig. 10g, h), similar to IAT. Sample BT06-15 is also depleted in bulk REEs (e.g. La = 1.4 ppm, Yb = 1.4 ppm versus N-MORB = 2.5 ppm La, 3.05 ppm Yb; Sun & McDonough, Reference Sun, McDonough, Saunders and Norry1989), resembling boninite. Lava flows are overlain by thick pyroclastic rocks with basaltic to dacitic sills. Basaltic sills (BT07-24 and BT06-25) have geochemical affinities with IAT, including approximately flat REE patterns (La_N/Yb_N ~ 0.8–1.8), Nb depletion (Nb/La ~ 0.4–0.5 × N-MORB) and Th enrichment (Th/La ~ 2.6–5.1 × N-MORB) (Fig. 10g, h). A pillow fragment in volcanic breccias (BT06-38) is calc-alkaline with LREE enrichment (La_N/Yb_N ~ 1.5) and strong negative Nb anomaly (Nb/La ~ 0.2 × N-MORB). Geochemical evolution from MORB to IAT and then into calc-alkaline and boninitic is characteristic of the lava sequence at Cheshmeh–Baghal. On a Ti v. V diagram (Shervais, Reference Shervais1982) (Fig. 9b), Balvard–Baft lavas plot mostly in the IAT field but also in MORB and boninite fields.