1 Introduction

The late Miocene–Pliocene volcanic rocks in Todeshk are significant constituents in the studied area. The volcanic rocks are situated in the middle of the Urumieh–Dokhtar magmatic arc (UDMA), about 120 km south-east of Isfahan (figure 1a). The UDMA is a large magmatic belt in the Zagros orogen, which is the result of the opening and closure of the Neo-Tethys Ocean (Alavi 1980, 2004; Omrani et al. 2008; Davoudian et al. 2016). The Zagros orogen is a part of the Alpine–Himalayan orogenic belt and consists of parallel tectonic subdivisions from the south-west to the north-east: (i) The Zagros simply folded belt and the main Zagros thrust, which is suggested to be the suture zone between Gondwana and Eurasia; (ii) the Sanandaj–Sirjan zone which is the internal part of the Zagros orogen consisting of metamorphic complexes and igneous plutons (Stöcklin 1968; Davoudian et al. 2016) and (iii) the UDMA, which is a subduction-related magmatic arc along the active margin of the Iranian plate (Berberian and Berberian 1981; Alavi 1994, 2004 Omrani et al. 2008). Magmatic activity in the UDMA created a wide belt of mostly Cenozoic volcanic and plutonic rocks. The UDMA is located between the Sanandaj–Sirjan zone and the Central Iran structural zone (figure 1a) (Berberian and Berberian 1981; Mohajjel et al. 2003). The maximum magmatic activity in the UMDA occurred in the Eocene period, but after a period of inactivity, has continued during the upper Miocene to the Plio-Quaternary (Omrani et al. 2008). However, the studies indicate that a collision occurred in the Oligocene–late Miocene, and although the active subduction between the Iranian edge of Eurasia and the Arabian plate as a part of Gondwana had ended, the magmatic activity did not stop (Berberian and Berberian 1981; Hassanzadeh 1993; Ghasemi and Talbot 2005; Omrani et al. 2008). The late Miocene to the Plio-Quaternary volcanism in the UDMA belongs to the post-collision magmatic activity which is probably the result of a break off the Neo-Tethys slab (Omrani et al. 2008). Magmatism in a subduction-related setting originates from the partial melting of the mantle wedge, lower crust, oceanic slab, slab sediments or releasing of fluids by the dehydration of the subducting oceanic slab (Tatsumi and Takahashi 2006). Pb isotope data can demonstrate the origin and proportion of involvement of mantle, slab, sediments or continental crust in the generation of parental magma. \({}^{204}\hbox {Pb}\) is non-radiogenic, while \({}^{208}\hbox {Pb}/{}^{204}\hbox {Pb}\), \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb}\) and \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\) increase during U and Th decays (Faure 1986). The most important mantle sources are identified by isotopic features as depleted mid-ocean ridge basalts (MORBs) or the depleted MORB mantle (DMM), high mu, \(\hbox {mu} = {}^{238}\hbox {U}/{}^{204}\hbox {Pb}\) (HIMU), enriched mantle type I (EMI) and enriched mantle type II (EMII) (Faure 1986; Zindler and Hart 1986). The HIMU sources were generated when the subducted oceanic crust was dehydrated and remained in the deep mantle for a long period. The HIMU have high U/Pb, Th/Pb and Sr/Rb ratios and indicate the radiogenic evolution of \({}^{206}\hbox {Pb}\) and \({}^{207}\hbox {Pb}\) (Wilson 1989). The DMM reservoirs have a U-depleted composition. The EMI has a geochemical composition similar to the lower crust or marine pelagic sediments as reported from carbonatite metasomatism in the lithospheric mantle (White 2003; Lustrino and Anderson 2015). The EMI sources have high Th/U and low U, Th/Pb ratios, negative anomalies of Hf, Zr and positive anomalies of Eu. EMI can be formed by recycling the lower continental crust or subducted pelagic sediments (White 2003; Lustrino and Anderson 2015; Yamgouot et al. 2016). The EMII mantle end-member is characterised by the \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\) intermediate between EMI and HIMU, a relatively high \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb}\) ratio (for a given \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\)), negative anomalies of Nb, Ta and the lack of positive anomalies of Eu. The EMII has been reported from subduction environments and perhaps modified by recycling the oceanic crust and subducted terrigenous sediments. The \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr}\) ratios of EMI–EMII are higher than DMM and bulk silicate earth or the primary uniform reservoir (White 2003; Workman et al. 2004; Lustrino and Anderson 2015; Yamgouot et al. 2016). Generally, the elements Pb, Th and U are concentrated in the continental crust, and the Pb isotopic composition of the mantle is sensitive to the crustal components. Therefore, the isotopic compositions of HIMU, EMI and EMII are mainly related to recycling subducted lithologies such as the oceanic crust, pelagic or terrigenous sediments and the lower continental crust. In the absence of oxygen isotopic data, we have applied the new whole rock Pb, Sr and Nd isotopic ratios together with major and trace elements to determine the magmatic source of the late Miocene–Pliocene volcanic rocks in Todeshk, in the south-east of Isfahan as a central part of UDMA.

Fig. 1
figure 1

(a) Position of the studied area in the structural units of Iran (Mohajjel et al. 2003) and (b) the geological map of the studied area (simplified from the geological map of 1:250,000 Nain, Nabavi and Amidi 1978).

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Fig. 2
figure 2

Representative photomicrographs for dacites (a) consisting of plagioclase phenocrysts and microphenocrysts of amphibole, biotite, quartz and (b) quartz and plagioclase in felsitic groundmass (CPL, field of view 4 mm), representative photomicrographs of andesites, (c) comprising plagioclase, pyroxene and amphibole with a glomeroporphyritic texture and (d) comprising plagioclase and pyroxene with a porphyritic texture (CPL, field of view 4 mm). Bi \(=\) biotite, Amp \(=\) amphibole, Px \(=\) pyroxene, Pl \(=\) plagioclase, and Qz \(=\) quartz.

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Table 1 Whole-rock isotopic data of volcanic rocks.
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Fig. 3
figure 3

Classification of the volcanic rocks in the TAS diagram (Cox et al. 1979; data from Khodami et al. 2010).

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Fig. 4
figure 4

(a) Chondrite-normalised REE element patterns of volcanic rocks (chondrite-normalising values are from Nakamura (1974). (b) Primitive mantle-normalised patterns of volcanic rocks. Normalising values are from Sun and Mcdonough (1989) (data from Khodami et al. 2010).

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Fig. 5
figure 5

(a) La/Yb vs. Yb diagram, (b) Th /La vs. Ce/Pb diagram, (c) Th/Yb vs. Ba/La diagram and (d) Ba/Th vs. La/Sm diagram of volcanic rocks (Wang et al. 2006; Arslan et al. 2013; Qian et al. 2016; data from Khodami et al. 2010).

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Fig. 6
figure 6

Th/Yb vs. Nb/Yb diagram (Pearce (2008), N-MORB, E-MORB, OIB are from Sun and Mcdonough (1989), average continental crust is from Rudnick and Fountain (1995) and subducted sediment trench averages are from Plank and Langmuir (1998)). (White box subducted sediment, red circles (table 1) and white circles are from the north-west of Isfahan, data from Khodami 2011).

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Fig. 7
figure 7

(a) Sr isotope ratios vs. \(\hbox {SiO}_{2}\) and (b) MDI = \((1/3 \hbox { SiO}_2+\hbox {K}_2\hbox {O})-(\hbox {CaO}+\hbox {MgO})\) diagrams (Wang et al. 2006; Arslan et al. 2013; data from Khodami et al. 2010).

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Fig. 8
figure 8

Plots of Sr–Nd–Pb isotopic ratios for the volcanic rocks: (a)\({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr}\) vs. \({}^{143}\hbox {Nd}/{}^{144}\hbox {Nd}\) diagram, (b) \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr}\) vs. \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\) diagram; mantle components including depleted mantle (DM), enriched mantle I (EMI), enriched mantle II (EMII), high U/Pb mantle (HIMU) are from Zindler and Hart (1986). Red circles (table 1) and star symbols (data from Khodami and Davoudian 2008) show the late Miocene–Pliocene volcanic rocks from the south-east of Isfahan, and white circles are from the north-west of Isfahan (data from Khodami 2011).

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2 Geological setting

The late Miocene–Pliocene volcanic rocks in the UDMA outcrop in the south-east and north-west of Isfahan with a NW–SE trend. The studied area is located 130-km south-east of Isfahan and near Todeshk. The Cretaceous units are also observable in the north of the area, consisting of limestone and slightly metamorphosed volcanic rocks. However, most of the magmatic activity occurred in the Eocene, including varieties of the volcanic and the volcano-sedimentary rocks. Miocene reddish-grey conglomerate and sandstone as Red formation are the other lithological units (Nabavi and Amidi 1978). The andesitic lava flows across the Upper Red formation. The dacitic domes and lava domes intruded into the andesite and probably they belong to the latest volcanic activity in the area (figure 1b) (Nabavi and Amidi 1978). Based on stratigraphy, the volcanic rocks were emplaced during the late Miocene–Pliocene after the collision between the Iranian and Arabian platforms. One available K–Ar age dating for a dacitic dome has exhibited \(14.1\,\pm \,0.8\,\hbox {Ma}\) (Ghorbani et al. 2014). The dacites consist of plagioclase and various amounts of orthopyroxene, amphibole, biotite, quartz and opaque oxides, set in a colourless to pale brown glass or felsitic groundmass (figure 2a and b). The andesites contain abundant phenocrysts of plagioclase, pyroxene or amphibole, biotite and opaque oxides, set in a brown glass matrix with microlites of plagioclase and microphenocrysts of pyroxene or amphibole (figure 2c and d). The most abundant mineral is plagioclase, and its textures are mainly porphyritic.

3 Materials and methods

The Sr, Nd and Pb isotopic ratios of five samples of the volcanic rocks are presented in table 1. For the Sr–Nd–Pb isotopic determination, the late Miocene–Pliocene volcanic rocks were analysed using the multi-collector ICP-MS (Nu Plasma) at the State Key Laboratory of Continental Dynamics, Northwest University, China. Also, the available isotopic data of the late Miocene–Pliocene volcanic rocks from the north-west of Isfahan are considered to make a conclusion (Khodami 2011). The Sr and Nd isotopic ratios were corrected for mass fractionation relative to \({}^{86}\hbox {Sr}/{}^{88}\hbox {Sr} = 0.1194\) and \({}^{146}\hbox {Nd}/{}^{144}\hbox {Nd} = 0.7219\), respectively. The BCR-2 standard yielded an \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr}\) ratio of \(0.704959\,\pm \,36\) and \({}^{143}\hbox {Nd}/{}^{144}\hbox {Nd}\) ratio of \(0.512613\,\pm \,19\), compared with its reported \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr}\) ratio of 0.704958 and \({}^{143}\hbox {Nd}/{}^{144}\hbox {Nd}\) ratio of 0.512633. Pb isotopic fractionation was normalised to \({}^{205}\hbox {Tl}/{}^{203}\hbox {Tl} = 2.3875\). Within the analytical period, measurements of NBS SRM981 gave average values of \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb} = 16.942\,\pm \,0.0014 (2\sigma )\), \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb} = 15.495\,\pm \,0.0014\) and \({}^{208}\hbox {Pb}/{}^{204}\hbox {Pb}=36.716\,\pm \,0.0032\). BCR-2 standard gave \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb} = 18.735\,\pm \,0.0009 (2\sigma )\), \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb} \,{=} 15.621\,\pm \,0.0008\) and \({}^{208}\hbox {Pb}/{}^{204}\hbox {Pb} \,{=}\, 38.684 \,\pm \, 0.0020\).

4 Discussion

4.1 Geochemistry

According to the geochemical studies of Khodami et al. (2010), the rocks have \(\hbox {SiO}_{2}\) content ranging from 55.73 to 65.63 wt% and these are medium to high K calc-alkaline and meta-aluminous. The rocks show a composition from andesite to dacite in total alkali against a silica diagram (figure 3) (Khodami et al. 2010). Furthermore, parts of the volcanic rocks have adakitic characteristics (Khodami et al. 2009). The chondrite-normalised rare-earth element (REE) patterns show light rare-earth element (LREE) enrichment and heavy rare-earth element (HREE) depletion without (europium) Eu anomaly (figure 4a). The primitive mantle-normalised multi-element diagram is characterised by the enrichment of large ion lithophile elements (LILEs) (Rb, Ba, K, Sr and especially Pb) and depletion in high field-strength elements (HFSEs) (Nb, Ta, P and Ti) (figure 4b) (Khodami et al. 2009, 2010). The negative Nb, Ta and Ti anomalies are indicative of subduction origin (Zhang et al. 2007). The enrichment of Sr without Eu anomaly and the depletion of HREE and Y suggest the absence of plagioclase and the existence of garnet as a residue in the source, respectively (Khodami et al. 2009, 2010). Slab-derived fluids and melts resulted in the enrichment of LILE and alkali elements. However, more preferential enrichment of Rb rather than that of K occurs (Zhang et al. 2007), and the HFSE (Nb, Ta, P and Ti) prefer to remain in phases such as rutile, ilmenite or amphibole by source (Pearce 1983; Wilson 1989). The rocks in the area have low contents of Nb/U (1.74–5) and Ce/Pb (0.47–4.03) (Khodami et al. 2009, 2010). The low Nb/U ratios display mantle metasomatism (Zhang et al. 2007). Also, the proportion of Ce as LREE to Pb as LILE is related to the special extraction of Pb from slab to mantle wedge, indicating more of the influence of subducted sediments (White 2003; Qian et al. 2016). The variations of La/Yb ratios against Yb show heterogeneity in the source region (figure 5a). Furthermore, Ba/Th vs. La/Sm, Th/La vs. Ce/Pb and Ba/La vs. Th/Yb diagrams indicate the involvement of slab-derived melts in the mantle source (figure 5b–d) (Wang et al. 2006; Arslan et al. 2013; Qian et al. 2016). In addition, the La/Nb vs. Th/Nb diagram can discriminate MORB–ocean island basalt (OIB) and three main crustal inputs: subduction, contamination with continental crust and crustal recycling during delamination (Pearce 2008). The subducted sediment averages are dispersed above the MORB–OIB array. The samples are plotted above the MORB–OIB array and scattered in the field of subducted sediments from the different subduction settings (figure 6). These geochemical features show that slab-derived melts and fluids are recycled into the mantle source.

Fig. 9
figure 9

Plots of Pb isotopic ratios for the volcanic rocks: (a) \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb}\) vs. \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\) diagram. (b) \({}^{208}\hbox {Pb}/{}^{204}\hbox {Pb}\) vs. \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\) diagram. (c) \({}^{208}\hbox {Pb}/{}^{206}\hbox {Pb}\) vs. \({}^{207}\hbox {Pb}/{}^{206}\hbox {Pb}\) diagram. Mantle reservoir including depleted mantle (DM), enriched mantle I (EMI), enriched mantle II (EMII) and high U/Pb mantle (HIMU) are from Zindler and Hart (1986) Reference lines after Zartman and Doe (1981). MORB data are from Mukasa et al. (1994) and Pb isotope ratios in main terrestrial reservoirs are from White (2003) (symbols are the same as those used in figure 8).

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Fig. 10
figure 10

(a) \(\Delta \) 8/4 Pb vs. \(^{206}\)Pb/\(^{204}\)Pb diagram. (b) \(\Delta \)7/4 Pb vs. \(^{206}\)Pb/\(^{204}\)Pb diagram (Arslan et al. 2013). The mantle reservoirs identified by Zindler and Hart (1986) and Hofman (1997); northern hemisphere reference line (NHRL) from Hart (1984) (symbols are the same as those used in figure 8).

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4.2 Isotope features

The volcanic rocks show limited variations in Pb, Sr and Nd isotopic compositions with \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb} = 18.41\)–18.72; \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb} = 15.64\)–15.67; \({}^{208}\hbox {Pb}/{}^{204}\hbox {Pb} = 38.49\)–38.83; \({}^{207}\hbox {Pb}/{}^{206}\hbox {Pb} = 0.8372\)–0.8496; \({}^{208}\hbox {Pb}/{}^{206}\hbox {Pb} = 2.0743\)–2.0905; \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr} = 0.7051\)–0.7068 and \({}^{143}\hbox {Nd/}^{144}\hbox {Nd} = 0.5125\). The rocks also have a \({\Delta }7/4\hbox {Pb}\) range of 15.44–15.82 and a \({\Delta }8/4\hbox {Pb}\) range of 57.26–60.44 (table 1). As mentioned above, the geochemical features suggested an enrichment mantle source. Also, based on the isotopic ratios of Pb, Sr and Nd, major and trace elements, the origin of magma and the role of crustal components have been studied. Crustal contamination results in a significant increase in \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr}\) ratios and a positive correlation with \(\hbox {SiO}_{2}\) (Wang et al. 2006; Gao et al. 2007) but this correlation is not observed for the \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr}\) vs. \(\hbox {SiO}_{2}\) diagram for the volcanic rocks in the area (figure 7a). Moreover, the Sr isotope ratios are plotted against the magmatic differentiation index (MDI) and show metasomatism at source (figure 7b). Both diagrams show that magma escaped from contamination by crustal components during magma ascension and composition variations of the rocks have been controlled by metasomatism processes at source.

Moreover, the \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr}\) ratio in the rocks is higher than MORB and DMM, showing the addition of more radiogenic Sr to the mantle source (Lustrino and Anderson 2015). The volcanic rocks plot in the mantle array towards the EMII in the \({}^{143}\hbox {Nd}/{}^{144}\hbox {Nd}\) vs. \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr}\) diagram (figure 8a). The rocks have a high isotopic composition of Sr and Pb compared to DMM and EMI, and their isotopic composition is scattered towards the EMII in the \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\) vs. \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr}\) diagram (figure 8b). Nevertheless, the \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr}\) ratio shows amounts lower than the EMII. The volcanic rocks have \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\) and \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb}\) ratios more than the EMI, DMM and the lower continental crust, and a \({}^{208}\hbox {Pb}/{}^{204}\hbox {Pb}\) ratio higher than the DMM. Despite the small number of analyses, the data are well ranged in the Pb isotopes diagram and plotted near the EMII field (figures 8 and 9). Thoroughly in the \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb}\) vs. \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\), \({}^{208}\hbox {Pb}/{}^{204}\hbox {Pb}\) vs. \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\) and \({}^{208}\hbox {Pb}/{}^{206}\hbox {Pb}\) vs. \({}^{207}\hbox {Pb}/{}^{206}\hbox {Pb}\) diagrams, the volcanic rocks are plotted in the EMII or scattered towards the EMII field (figure 9a–c). Moreover, they are formed in the orogenic setting (figure 9a). The volcanic rocks have high amounts of radiogenic Pb ratios, positive \({\Delta }7/4\) and \({\Delta }8/4\hbox { Pb}\), and plots above the north hemisphere reference line (NHRL) (figure 10a and b). The \({\Delta }8/4\hbox {Pb}\) values indicate high Th/U ratios, enrichment of radiogenic \({}^{208}\hbox {Pb}\) and probably the involvement of the crustal components in the source (Arslan et al. 2013). Also, the high \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb}\) ratios suggest the addition of more radiogenic Pb components to the source of magma. The \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb}\) ratio in the crust is more than that in the mantle and this ratio is sensitive to crustal components enrichment (Workman et al. 2004; Wang et al. 2006; Ge et al. 2015). The values of \({}^{208}\hbox {Pb}/{}^{204}\hbox {Pb}\) and \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb}\) vs. \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\) of volcanic rocks display enrichment by crust materials such as marine sediments or continental crust (figure 11a and b) (Arslan et al. 2013). Oceanic crust has high U and Th contents compared to the mantle due to their pelagic and terrigenous sediments (Wilson 1989; White 2003; Lustrino and Anderson 2015). As mentioned above, EMI and EMII are produced when pelagic (i.e., deep sea) and terrigenous (i.e., continental) sediments accompanied by slab are subducted in the mantle wedge and modified mantle. The Pb-isotope data are comparable to marine sediments such as those of the Atlantic and Indian oceans (figure 11c) (White 2003). The rate of mantle metasomatism is related to the composition of the slab and the degree of alteration and proportion of pelagic to terrigenous sediments (Workman et al. 2004; Lustrino and Anderson 2015). EMII type was created by the subduction of the oceanic crust and their terrigenous sediments comparable to the upper crust (Zindler and Hart 1986; Zhang et al. 2007). Thus, the marine sediments have a significant influence on the variation of isotopic ratios and geochemical features in the subduction environment. The oceanic crust and continental-derived sediments (terrigenous sediments) were recycled into the mantle wedge. Then, the enrichment of incompatible elements and the evolution of Pb isotopic ratios occurred in the mantle wedge. Pb is concentrated in phases such as feldspars and clays, while Sr is concentrated in carbonate-rich sediments (White 2003), which is reflected in the isotopic composition of magma in the metasomatised mantle. Nevertheless, the amounts of Sr and Nd could remain in the range of mantle composition that is interpreted by the inadequacy in time for the Sr radiogenic evolution in the source or marine sediments composition (Mukasa et al. 1994; White 2003). Furthermore, Sr, Nd and Pb isotopic and geochemical data do not support the assimilation of crustal materials in the magma source for the volcanic rocks. Evidence also suggests the rapid ascent of magma. The calc-alkaline and related adakitic rocks from Tudeshk, the central part of the UDMA, show the partial melting of the enriched mantle source. Thus, it is possible that some adakitic volcanic rocks in UDMA are derived from a metasomatised mantle wedge (Azizi et al. 2014).

Fig. 11
figure 11

Plots of Pb isotopic ratios of volcanic rocks (Arslan et al. 2013): (a) \({}^{208}\hbox {Pb}/{}^{204}\hbox {Pb}\) vs. \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\) diagram. (b) \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb}\) vs. \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\) diagram. The mantle reservoirs were identified by Zindler and Hart (1986). Pb isotopic ratios in the major terrestrial reservoirs are from White (2003). (c) \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb}\) vs. \({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb}\) diagram, showing data from the studied area compared with the Atlantic, Pacific and Indian MORB and marine sediments from Atlantic, Pacific and Indian oceans (White 2003) (symbols are the same as those used in figure 8).

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5 Conclusion

The late Miocene–Pliocene volcanic rocks in the south-east of Isfahan show mainly calc-alkaline to adakitic trends with relatively high LILE and LREE and low HFSE abundances. Depletion in the Nb, Ta and Ti and the Nb/La, Nb/U, La/Yb, Ba/Th, La/Sm, Th/Yb, Th/La, Ba/La and Ce/Pb ratios indicate heterogeneity in the mantle source. Sr, Nd and Pb isotopic ratios and whole-rock geochemical data from the late Miocene–Pliocene volcanic rocks in the south-east of Isfahan present new results with regard to the generation of post-collisional volcanism in UDMA. The results are as follows:

  1. 1.

    The studied volcanic rocks have a narrow range of \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr}\) (0.7051–0.7068) \({}^{143}\hbox {Nd/}^{144}\hbox {Nd}\) (0.5125) and Pb isotopic compositions (\({}^{206}\hbox {Pb}/{}^{204}\hbox {Pb} = 18.41\)–18.72, \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb} = 15.64\)–15.67, \({}^{208}\hbox {Pb}/{}^{204}\hbox {Pb} = 38.49\)–38.83), which demonstrate an enrichment mantle source.

  2. 2.

    The correlation between some elements and isotopes shows that crustal assimilation did not play a significant role in the geochemical and isotopic variation of the volcanic rocks.

  3. 3.

    Sr, Nd and Pb isotopic data suggest the involvement of EM-like mantle sources. The lower \({}^{143}\hbox {Nd}/{}^{144}\hbox {Nd}\), higher \({}^{87}\hbox {Sr}/{}^{86}\hbox {Sr}\), \({}^{207}\hbox {Pb}/{}^{204}\hbox {Pb}\) and \({}^{ 208}\hbox {Pb}/{}^{204}\hbox {Pb}\) than MORB are very similar to the EMII-type that need an additional subducted sediments involvement. Oceanic crust and terrigenous sediments were recycled into the mantle wedge and resulted in the enrichment of incompatible elements and the evolution of Pb isotopic ratios.

  4. 4.

    The late Miocene–Pliocene calc-alkaline and adakitic magma from Todeshk, south-east of Isfahan could be produced with an enriched mantle source. In this case, the role of the EMII has dominated over the other mantle end-members. The origin of the EMII involves the metasomatism of the mantle lithosphere, followed by the subduction and recycling of continental sediments related to the slab.