Eocene Kashmar Granitoids (NE Iran): Petrogenetic Constraints from U–Pb Zircon Geochronology and Isotope Geochemistry

Lithos 216–217 (2015) 118–135

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Eocene Kashmar granitoids (NE Iran): Petrogenetic constraints from U–Pb zircon geochronology and isotope geochemistry

Hadi Shafaii Moghadam a,b,⁎, Xian-Hua Li b, Xiao-Xiao Ling b,JoseF.Santosc,RobertJ.Sternd, Qiu-Li Li b, Ghasem Ghorbani b a School of Earth Sciences, Damghan University, Damghan 36716-41167, Iran b State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China c Geobiotec, Departamento de Geociências, Universidadede Aveiro, 3810-193 Aveiro, Portugal d Geosciences Department, University of Texas at Dallas, Richardson, TX 75083-0688, USA article info abstract

Article history: Kashmar granitoids outcrop for ~100 km along the south ﬂank of the Sabzevar ophiolite (NE Iran) and consist of Received 12 August 2014 granodiorite and monzogranite along with subordinate quartz monzonite, syenogranite and aplitic dikes. These Accepted 14 December 2014 granitoids intruded Early to Middle Eocene high-K volcanic rocks and can spatially be grouped into eastern and Available online 26 December 2014 western granitoids. Five samples of granite have identical zircon U–Pb ages of ca. 40–41 Ma. The granitoids have quite high K O(~1.3–5.3 wt.%) and Na O(~1.1–4.6 wt.%) with SiO ranging between ~62 and 77 wt.%. They are Keywords: 2 2 2 metaluminous to peraluminous, calc-alkaline and I-type in composition. Their chondrite-normalized REE pat- I-type granite U–Pb zircon dating terns are characterized by LREE enrichment and show slight negative Eu anomalies. Kashmar granitoids have 18 Hf–Oisotopes low whole rock εNd (−0.43 to −2.3), zircon εHf values (−1.9 to +7.2), and somewhat elevated δ O (+6.1 Eocene magmatism to +8.7‰) in the range of I-type granites. The Kashmar granitoids show Early Neoproterozoic zircon second- Kashmar granitoids stage Hf and bulk rock Nd model ages at ca. 500–1000 Ma (associated with ca. 640 Ma old inherited zircons). Bulk rock Nd–Sr isotopic modeling suggests that 10–20% assimilation of Cadomian lower crust by juvenile mantle melts and then fractional crystallization (AFC process) can explain the Sr–Nd isotopic compositions of Kashmar granitoids. Kashmar granitoids are products of crustal assimilation by mantle melts associated with extension above the subducting Neotethyan Ocean slab beneath SW Eurasia. Similar subduction-related extension was responsible for the ﬂare-up of Eocene–Oligocene magmatism across Iran, associated with core complex formation in central Iran. © 2014 Elsevier B.V. All rights reserved.

1. Introduction extension following crustal thickening by continental collision (e.g., Barbarin, 1999; Jiang and Li, 2014; Li et al., 2007; Roberts and It is important to understand the origin of I-type granitic melts be- Clemens, 1993). cause these make up much of the continental crust and often host min- The Zagros orogen is a complex architecture of repeated accretion eral deposits. It is generally believed that high-K, I-type granites may and collision events of continental blocks and consequent arc derive from melting of hydrous intermediate to maﬁchigh-Kmeta- magmatism (Castro et al., 2013). The Zagros orogeny highlights several igneous rocks (e.g., Roberts and Clemens, 1993; Sisson et al., 2005) phases of subduction, collision and post-collisional extension associated and/or from mixing of mantle-derived magmas with crustal-derived with extensive Cretaceous to Cenozoic magmatism to form the melts (e.g., Hildreth et al., 1991; Huang et al., 2013). Assimilation of Urumieh–Dokhtar magmatic assemblage (UDMA) and Alborz Magmat- metapelites by basaltic magmas has also been suggested for the gener- ic Belt in N-NW Iran (e.g., Agard et al., 2011; Castro et al., 2013). The ating I-type granitoids (e.g., Castro et al., 1999; Patino-Douce, 1995). Urumieh–Dokhtar magmatic assemblage is a 50–80 km wide Andean- High-K calc-alkaline granites are rare in anorogenic settings but type magmatic belt of intrusive and extrusive rocks formed by oblique common in convergent margin environments, particularly in post- northeastward subduction of Neo-Tethyan ocean ﬂoor beneath Iran collisional settings (e.g., Barbarin, 1999; Kemp et al., 2009; Roberts (Fig. 1)(Agard et al., 2011; Alavi, 1994; Berberian and King, 1981; and Clemens, 1993). A favorable tectonic setting for forming calc- Berberian et al., 1982; Falcon, 1974; Shahabpour, 2005), followed by alkaline, I-type granites is post-orogenic collapse and post-collision collision between the Anatolian–Iranian and Arabian plates beginning in Middle to Late Miocene time (Berberian and King, 1981; Sen et al., 2004). This magmatic assemblage includes a thick (~4 km) pile of ⁎ Corresponding author at: State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China. early calc-alkaline and late shoshonitic as well as alkaline rocks. E-mail address: [email protected] (H. Shafaii Moghadam). Subduction-related igneous activity in Iran has been continuous from

TURKMENISTAN Khoy Sabzevar magmatic belt Caspian Sea

Quchan

Mashhad Sabzevar o 34 Takab Urumieh-Dokhtar magmaticTehran arc Biarjmand Cadomian crust Kashmar Torbat-Hey.

AFGHANIS Kermanshah Dorouneh Fault

Golpayegan Birjand Zagros Fold-Thrust Belt Saghand NainYazd Block TAN Kerman-Kashmartectonic zone

IRAQ Tabas Block

o 30 Lut Block Shahr-e-Babak

Neyriz Baft

Haji-Abad Persian Gulf Kahnuj Iranshahr

o 26 Fanuj-Maskutan

200 km Gulf Of Oman o o o 50 54 58

Sanandaj-Sirjan Zone Neogene volcanism

Makran Zone Eocene magmatic rocks

Alborz Zone Mesozoic magmatic rocks

Eastern Iranian Suture Zone Ophiolitic Suture Zone

Kopet-Dagh Zone Eocene core complex

Fig. 1. Simpliﬁed geological map of Iran showing the distribution of Eocene magmatic rocks. The distribution of core complexes is according to Verdel et al. (2007).

Cretaceous until today, but peak activity was in Eocene to Oligocene Paleocene to Early Eocene and Oligo-Miocene (Shafaii Moghadam time (Amidi et al., 1984; Berberian and King, 1981). Eocene magmatism et al., unpublished data) also occur along the southern Sabzevar is also conspicuous in NE-NW Turkey (Altunkaynak et al., 2012), for ophiolites. These rocks may show pulses of subduction-related (Creta- which convective removal or partial delamination of mantle lithosphere ceous–Paleocene) and post-orogenic magmatism (Eocene-Oligo-Mio- and its replacement by hot asthenosphere are considered as possible cene) within the Sabzevar magmatic belt. The rocks have juvenile mechanisms to produce voluminous Eocene igneous rocks. and/or recycled characteristics evidenced by variable bulk rock εNd Related to development of the SW Eurasian arc, Cenozoic igneous ac- and zircon εHf values (Shafaii Moghadam et al., unpublished data). tivity in central-NE Iran was voluminous and widespread, especially South of the Sabzevar-Torbat-e-Heydarieh ophiolites, a large mag- during Eocene–Oligocene time. The Sabzevar magmatic belt of NE Iran matic belt N250 km long and N90 km wide developed during Late Cre- contains widespread Cenozoic magmatic rocks (Fig. 1), distributed taceous to Plio-Quaternary time (Fig. 2). This belt is dominated by mainly south of the Late Cretaceous Sabzevar-Torbat-e-Heydarieh plutons of the Kashmar batholith and associated volcanic rocks along ophiolites, but also crosscutting the ophiolites and to the north. These the northern side of the Dorouneh Fault that are regarded as major com- are mostly intermediate to felsic intrusions and volcanic edifices. Rare ponents of a Paleogene Andean-type convergent margin. These could studies of these volcanic rocks identify calc-alkaline signatures for the represent the eastern continuation of the Urumieh–Dokhtar magmatic lava flows and adakitic characteristics for the felsic domes (Ghasemi arc (UDMA) of central Iran (Berberian and King, 1981). et al., 2010; Spies et al., 1983). It has been assumed that adakites are In this paper, we report new petrographic, geochemical, U–Pb zircon of Plio-Quaternary age, whereas intermediate to felsic lava flows and ages and isotopic (zircon Hf–O and whole rock Sr–Nd) data for the pyroclastic rocks are Eocene but new Ar–Ar as well as U–Pb zircon Kashmar granitoids of NE Iran. This is the first detailed study of granitic data (Shafaii Moghadam et al., unpublished data) shows that the magmatism in this region. We collected samples from both the eastern adakites are also Eocene. Granitoids as well as volcanic rocks with parts of the Kashmar batholith (north of Azghand; samples with K12- ages between Late Cretaceous (~99 Ma; Alaminia et al., 2013), prefix, see next sections) and the western parts (north of Kashmar; 120 .SaaiMgaa ta./Lto 216 Lithos / al. et Moghadam Shafaii H. – – 118 (2015) 217 135

Fig. 2. Geological map of the Sabzevar-Torbat-e-Heydarieh region, north of the Dorouneh Fault, with emphasis on the distribution of ophiolitic and magmaticrocks. H. Shafaii Moghadam et al. / Lithos 216–217 (2015) 118–135 121 samples with KR12-prefix) to see if there are geochemical or age varia- limestone, chert and volcaniclastic rocks, dissected by post-orogenic tions among the eastern and western parts. Our new data show that strike-slip faults (Rossetti et al., 2014). A metamorphic complex these granitoids define a marked Mid- to Late Eocene magmatic pulse consisting of Early Cretaceous (ca. 106–107 Ma) blueschists and am- and that these magmas reflect assimilation of Iranian Cadomian (Edia- phibolites and Late Paleocene (ca. 58 Ma) adakitic granites occupies caran–Cambrian) crust by mantle melts following fractional crystalliza- the frontal part (Nasrabady et al., 2011; Rossetti et al., 2010; Rossetti tion (AFC). Our results have important implications for understanding et al., 2014). the geodynamic framework of Eocene UDMA magmatism in Iran. Kashmar granitoids are located along the NW edge of the Lut Block within the Kerman–Kashmar Tectonic Zone (Ramezani and 2. Geological background Tucker, 2003), a nearly 600 km long, arcuate and structurally complex fault-bounded belt separating the Tabas and Yazd blocks. This Most tectonic reconstructions for closure of Neotethys agree that an tectonic zone exposes deeper sections of the central Iran basement active margin formed along southern Eurasia from Late Mesozoic and may be part of a regional core complex. Cadomian igneous and through Cenozoic time (e.g., Berberian and King, 1981; Moghadam metamorphic units (Taknar complex) are widely exposed northwest and Stern, 2011). Two main Cenozoic collisional phases have been rec- of the Kashmar granitoids and record a prolonged deformation history. ognized in central and NE Iran including; 1 — Neogene collision be- A previous Rb–Sr geochronological study showed that Kashmar granit- tween Iran and Arabia and 2 — Paleocene collision between central oids formed in Middle Eocene time (ca. 42 Ma; Soltani, 2000), and are Iran and Eurasia to close the Sabzevar basin. associated with high-K andesitic Early–Middle Eocene volcanic rocks. Widespread arc magmatism accompanied subduction of Neotethyan Field observations show that the Kashmar granitoids are shallow lithosphere beneath central Iran, within the overriding plate, with a leucogranite–granodiorite to monzogranites (Fig. 4A) with abundant major pulse during Middle Eocene time (e.g., Berberian and King, centimetric (~10–20 cm) to metric (~1 m) aplitic and micro- 1981; Chiu et al., 2013; Verdel et al., 2011). Geochronological data from granodioritic dikes (Fig. 4B). Aplitic dikes are abundant north of the volcanic arcs in central and N-NW Iran constrain the duration of Kashmar (western Kashmar batholith) whereas granodioritic and the magmatic pulse to ∼17 Myr, from ~54 Ma until 37 Ma (Verdel dacitic dikes are common in the Azghand section (eastern Kashmar et al., 2011). Transition from an extensional to a compressional plate batholith). The granitoids intruded subaerial Paleocene–Eocene pyro- margin along the Arabia–Eurasia convergence zone occurred during Eo- clastic and Early to Middle Eocene mafictofelsicvolcanicrocks cene time, associated with collapse of thickened crust of Central Iran (Fig. 3); Kashmar plutons and these volcanics may be intrusive and ex- (Rossetti et al., 2014). Orogenic collapse was accompanied by extension trusive equivalents. The E-W elongate nature of the batholith, with vol- and exhumation of metamorphic core complexes, best identified in cen- canic rocks to the north, suggests a regional volcano-plutonic complex tral Iran (Fig. 1)(e.g.,Ramezani and Tucker, 2003; Verdel et al., 2007). that has been uplifted and tilted north. Exhumation of metamorphic core complexes in central Iran, normal faulting and subsidence as well as widespread igneous activities are 3. Petrography and mineral chemistry striking manifestations of a Late Paleocene–Eocene episode of linked magmatic flare‐up and extension (Verdel et al., 2011). Verdel et al Locations of samples investigated in this study are shown in Fig. 3. (2011) attributed the flare‐up to decompression melting of lithospheric About 100 thin sections of Kashmar granitoids, their enclaves/dikes mantle hydrated by slab‐derived fluids, followed by Oligocene upwell- and volcanic rocks were examined (see Supplementary Document 1 ing and melting of less-modified asthenospheric mantle. This latest for analytical methods). phase was accompanied by eruption of alkaline olivine basalts in Kashmar granitoids are mostly homogenous, but are fine-grained central-NE Iran as well as NW Iran. near contacts with volcanic rocks; these contacts are occasionally Northeastern Iran is a complex magmatic-sedimentary zone with mylonitic. It is a single batholith, which consists mainly of monzogranite several juxtaposed blocks including the Lut block in the south, the and granodiorites along with minor quartz monzonite and syenogranite. Kopet-Dagh (Turan = Eurasia) block in the north and the Alborz zone Microgranular enclaves and volcanic xenoliths are present (Fig. 4Cand in the northwest, separated by the Sabzevar suture (Fig. 1). In NE Iran, D) and are especially abundant in the eastern batholith, north of Cretaceous to Eocene I-type granitoids outcrop over ~8000 km2 be- Azghand. Tourmaline-rich cataclastic veins are common in these granit- tween the Sabzevar-Torbat-e-Heydarieh ophiolites to the north and oids. Granodioritic to porphyritic dacitic dikes crosscut both granitoids the Dorouned fault to the south (Fig. 2). The Sabzevar-Tobat-e- and their host volcanic rocks, demonstrating close genetic association. Heydarieh ophiolite belt extends E-W for over 400 km and is part of Monzogranites show coarse-grained granular texture with the northern branch of the Neotethys Ocean (the Sabzevar Ocean) perthitic and myrmekitic intergrowths (Fig. 5B). Graphic texture is that opened during Early Cretaceous time as an embryonic oceanic common. Quartz, alkali feldspar, plagioclase and biotite are the basin and closed during Early Paleocene time (Shafaii Moghadam main components, along with minor amphibole and clinopyroxene. et al., 2014). Baroz et al. (1984) distinguished four lithostratigraphic Apatite, zircon and iron oxides are accessory phases. Granodiorites units, from Campanian in the lower parts to Paleocene in the upper are predominant and include plagioclase, alkali-feldspar (orthoclase parts of Sabzevar ophiolites, including alkaline to calc-alkaline pillow and microcline), quartz, amphibole, biotite and rare large crystals of lavas, litharenites, breccias and agglomerates with pelagic sediments. clinopyroxene (Fig. 5A and C). Plagioclase is coarse-grained (2– Their geodynamic reconstruction included: 1) generation of oceanic 4 mm) and locally altered into sericite. Apatite, zircon, titanite, and crust in a back-arc basin in middle to Late Cretaceous times; 2) deposi- iron oxides are minor phases while chlorite and epidote are second- tion of the volcano-sedimentary series, fed by a Late Cretaceous–Paleo- ary components. Clinopyroxene is converted into green amphibole cene arc; and 3) collision of the arc with the Lut block. Berberian and along margins and fractures (Fig. 5C). Quartz monzonites have simi- King (1981) considered that Sabzevar ophiolites, like the Nain-Baft lar mineralogy to monzogranites but with more plagioclase. Plagio- ophiolites to the south (Fig. 1), are related to a seaway that surrounded clase in the plutonic rocks has variable anorthite contents, from AN the Lut Block. Shojaat et al. (2003) suggested that the Sabzevar ophiolite 19.7 (oligoclase) to 53.6 (labradorite) (Supplementary Document was emplaced during NE-dipping subduction and Noghreyan (1982) 2A). Amphiboles are magnesio-hornblende with TiO2 and Na2Ocon- proposed formation in a back-arc basin, based on the geochemistry of tents between 0.7–1.3 and 0.9–1.4 wt.% respectively (Supplementary lavas and gabbros. U–Pb zircon age data for the Sabzebar ophiolites re- Document 2B). Biotite has Mg# from 0.48 to 0.53 and between 4.6 veals SSZ-type magmatism around ca. 100 to 78 Ma (Shafaii Moghadam and 4.9 wt.% TiO2 (Supplementary Document 2D). Enclaves have et al., 2014). The southern part of the Sabzevar belt consists of an accre- mostly granodioritic composition with small grains of plagioclase tionary complex made up of SSE-verging thrust slices of Late Cretaceous and amphibole, but dioritic enclaves with plagioclase, clinopyroxene 122 H. Shafaii Moghadam et al. / Lithos 216–217 (2015) 118–135

Western granitoids KR12-49 o - KR12-31; -33; -39 Eastern granitoids 35 20 K12-44

K12-32; -36; -38 KR12-34

KR12-46; -47; -51; -53 K12-16; -18; -19; -22H; 22E; 41.09±0.30 Ma KR12-19; -20; -22; -23 K12-48 K12-23G; -23D; -29 40.54±0.40 Ma K12-1; -3; -5; -8 -9 KR12-3; -7; -10; -14; -18 41.20±0.45 Ma K12-26 40.48±0.64 Ma Doruneh Fault 40.13±0.53 Ma 39.87±0.47 Ma o -

35 15 Kashmar

- 15 km - Azghand o o 58 30 58 50

Early Eocene andesitic Middle Eocene leucogranite Fault to dacitic rocks Middle Eocene granodiorite Paleocene-Early Eocene Sample location pyroclastic rocks -monzogranite

Fig. 3. Simpliﬁed geological map of the Kashmar granitoids showing sample localities (modiﬁed after Feyz-Abad and Kashmar 1/100000 maps).

Fig. 4. Field photographs of the Kashmar granitoids. A — Outcrops of Kashmar granitoids. B — Aplitic dike intruding Kashmar granitoids. C — micro-granular enclave in Kashmar granitoid. D — volcanic xenolith in the Kashmar granitoids. H. Shafaii Moghadam et al. / Lithos 216–217 (2015) 118–135 123

Fig. 5. Microphotographs of Kashmar granitoids. A — Clinopyroxene, quartz, alkali feldspar, plagioclase and biotite assemblages in the Kashmar monzogranite (sample KR12-20). B — Perthitic K-feldspar and biotite in granodiorite (KR12-22). C — Association of clinopyroxene (partly converted into green amphibole), biotite, alkali feldspar and plagioclase in granodiorite (K12-16). D — Perthitic K-feldspar and quartz in aplitic dikes (KR12-18). E — Orthopyroxene, clinopyroxene and plagioclase in dioritic enclaves (KR12-22). F — Altered plagioclase and vein-ﬁlled ﬁne-grained quartz in volcanic rocks. The glassy groundmass is altered into clay and iron oxides (KR12-49).

and orthopyroxene (Fig. 5E) are also common. Aplitic dikes have syenogranite–quartz monzonite fields. The sample (KR12-22) with dio- monzogranite composition and comprise perthitic orthoclase and/or ritic micro-enclaves plots in the diorite field. Dikes show monzogranitic microcline (N50 vol.%) and quartz (Fig. 5D). Granodioritic–dioritic to granodioritic affinity in the QAP diagram whereas enclaves have dikes comprise altered plagioclase and rare amphibole and biotite. Vol- granodioritic to quartz monzodioritic characteristics (Fig. 6A). canic rocks include quartz andesites with microphenocrysts of plagioclase, amphibole and rare quartz in a cryptocrystalline to glassy 4. Whole rock geochemistry groundmass (Fig. 5F). Dacites are also common with microphenocrysts of sanidine and quartz. 4.1. Major and trace elements In the Quartz–Alkali Feldspar–Plagioclase diagram (based on the normative minerals) (Fig. 6A) after Streckeisen (1979), the Kashmar Representative whole rock analyses of the Kashmar granitoids are granitoids (both the KR- and K-samples) plot predominantly in the presented in Supplementary Document 3. Western granitoids (Kashmar

ﬁeld of granodiorite but also in monzogranite and rarely in the section) have quite uniform compositions with 62.4–67.8 wt.%. SiO2 124 H. Shafaii Moghadam et al. / Lithos 216–217 (2015) 118–135

Q A B Foid-syenite 14 Foidolite Q-rich granitoid 12 Foid- monzosyenite

O Syenite 2 10 Foid- Granite monzogabbro Syeno- O+K 2 8 diorite tonalite Na Foid-gabbro 6 syeno- monzo- grano- granite diorite Diorite Grano- AF granitegranite 4 diorite Q- Q-monzodi Q-syenite monzonite 45 55 65 75 A syenite monzonite P SiO2 wt.%

C adakites Western gran. 1000 D Plutonic rocks Eastern gran. WPG Syn-ColG Western gran. Eastern gran. Volcanic rocks 100 Western gran. Dike & enclave Eastern gran. Rb Sr/Y VAG

10 arc dacites and rhyolites ORG Verdel et al., 2011

0 50 100 150 200 1 02040601 10 100 1000 Y (ppm) Y + Nb

3 12 E F Peraluminous Metaluminous 8 Alkalic 2

4 A/NK O+CaO (wt.%) 2 1

O+K Alkali-calcic 2 0

Na Calc-alkalic Calcic 0 -4 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 50 60 70 80

A/CNK SiO2 wt.%

Fig. 6. A — Quartz–Alkali feldspar–Plagioclase (QAP) normative classification diagram for Kashmar granitoids. B — Total alkalis versus SiO2 diagram for classification of the Kashmar rocks (after Lebas et al. (1986)). C — Sr/Y vs. Y diagram for discriminating adakites from arc dacites and rhyolites (the fields for adakite and normal island-arc dacites and rhyolites are based on the work of (Castillo (2006); Defant and Drummond (1990); Defant and Drummond (1993)). Kashmar granitoids and volcanics have low Sr/Y ratios similar to normal arc rocks. D — Rb vs. Y+Nbdiagram(Pearce et al., 1984) for Kashmar igneous rocks. Compositional field for the central Iranian magmatic rocks (red dashed line) are from Verdel et al. (2011).E— ANK (molar

Al2O3/Na2O+K2O) vs. A/CNK (molar Al2O3/CaO+ Na2O+K2O) diagram. F — Plot of Na2O+K2O-CaO vs. SiO2 (Frost et al., 2001) for Kashmar magmatic rocks.

(except sample KR12-22 with low SiO2; 50.98 wt.%), 1.3–4.2 wt.% volcanic arc granites (VAG) (Fig. 6D). Kashmar granitoids are K2Oand1.1–4.3 Na2O contents (Supplementary Document 3). The alkali-calcic to calc-alkalic and belong to the metaluminous to eastern granitoids (Azghand section) contain ~66–76.7 wt.% SiO2, peraluminous granitoid series, with A/CNK b 1.1 (molar Al2O3/ 1.01–5.3 wt.% K2Oand3.2–4.6 wt.% Na2O (Supplementary Document (CaO + K2O+Na2O)) (Fig. 6EandF). 3). Kashmar granitoids are mostly high-K granites; only two samples Kashmar western granitoids have LREE-enriched patterns (La(n)/ have low (~1%) K2O. Enclaves have 58.6–69.9 wt.% SiO2,2.5–3.9 wt.% Yb(n) =5.1–11.1), and show slightly negative Eu anomalies (Fig. 7A). K2Oand3.5–4.3 wt.% Na2O while dikes contain 61.9–76.8 wt.% SiO2, Enrichment in Rb, Ba, K, U, Th, Pb and depletion in Nb, Ta, and Ti rel- 4.2–5.5 wt.% K2Oand3.0–3.1 wt.% Na2O. In the total alkalis vs. silica ative to LREE is conspicuous (Fig. 7B). The Azghand eastern granit- diagram of LeBas et al. (1986), most Kashmar granitoids plot in the oids also have LREE-fractionated patterns with La(n)/Yb(n) = granodioritic and granitic fields (except sample KR12-22) while ap- 4.5–8.5. The samples have slight Eu depletion except sample K12-3 litic dikes tend to plot in the granitic domain (Fig. 6B). Most enclaves withamorenegativeEuanomaly(Fig. 7C). They are characterized plot in granodiorite to syenodiorite domains. The rocks have low Sr/ by enrichment in Rb, Ba, Th, U, K and Pb and negative anomalies in Y, distinct from adakites and similar to normal arc igneous rocks Nb, Ta, Ti and P. Depletion in Ti and P could reflect titanomagnetite (Fig. 6C). In the Rb against Y + Nb diagram (Pearce et al., 1984), and apatite fractionation, respectively. Enclaves are also enriched the Kashmar granitoids as well as volcanic rocks show affinities to in LREE relative to HREE (La(n)/Yb(n) =4.8–8.5) and large ion H. Shafaii Moghadam et al. / Lithos 216–217 (2015) 118–135 125

1000 plutonic rocks (Western section, Kashmar) A 1000 B

100 100

10 1

1 0.1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Rb Th Nb K Ce Pr P Zr Sm Eu Tb Y Er Yb Ba U Ta La Pb Sr Nd Hf Ti Gd Dy Ho Tm Lu 1000 plutonic rocks (Eastern section, Azghand) C 1000 D

100 100

10 1

1 0.1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Rb Th Nb K Ce Pr P Zr Sm Eu Tb Y Er Yb

Sample/Chondrite Sample/N-MORB Ba U Ta La Pb Sr Nd Hf Ti Gd Dy Ho Tm Lu 1000 E 1000 F aplitic dike (Kashmar)

100 100 monzogranitic enclave (Azghand) granodioritic dike 10 enclave (Azghand) 10 (Kashmar) granodioritic enclave 1 (Azghand)

1 0.1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Rb Th Nb K Ce Pr P Zr Sm Eu Tb Y Er Yb Ba U Ta La Pb Sr Nd Hf Ti Gd Dy Ho Tm Lu 1000 G 1000 H

porphyritic andesite (Kashmar) 100 100

10 porphyritic dacite (Azghand) 1

1 0.1 La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Rb Th Nb K Ce Pr P Zr Sm Eu Tb Y Er Yb Ba U Ta La Pb Sr Nd Hf Ti Gd Dy Ho Tm Lu

Fig. 7. Chondrite-normalized rare earth elements and N-MORB normalized trace element patterns for the Kashmar granitoids (A–F) and volcanic rocks (G–H).

lithophile elements (LILEs) and are depleted in high ﬁeld strength el- depletion. Kashmar granitoids and their associated dikes and en- ements (HFSEs) (Fig. 7E and F). Aplitic dikes also have LREE claves are similar to high-K, I-type calc-alkaline granites. Volcanic fractioned pattern (La(n)/Yb(n) ≈ 8–11) but with greater Eu rocks have similar calc-alkaline signatures with fractionated REE 126 H. Shafaii Moghadam et al. / Lithos 216–217 (2015) 118–135

patterns (La(n)/Yb(n) =7.7–9.8), depletion in Nb–Ta–Ti and enrich- 5. U–Pb dating and zircon Hf–O isotopes mentinRb,Ba,Th,U,K,andPb(Fig. 7 GandH). 5.1. U–Pb zircon dating

4.2. Whole rock Sr–Nd isotopes We dated three samples from the western Kashmar batholith (KR12-46, KR12-10 and KR12-15) and two samples from the eastern Sr–Nd isotopic analyses of the Kashmar granitoids are presented in part (K12-9 and K12-29). Supplementary Document 4 and plotted in Fig. 8. The initial 87Sr/86Sr for intrusive rocks including dikes and enclaves calculated at 40 Ma 5.1.1. Sample KR12-46 (monzogranite) ranges between 0.7047 and 0.7058 for eastern granitoids and 0.7052 Zircons from sample KR12-46 (western section) have broken- and 0.7097 for western granitoids (Supplementary Document 4). The anhedral to short prismatic shapes. Most are ﬁne-grained (N50 μm aplitic dike has high 87Sr/86Sr (0.7097). Volcanic rocks have similar long). In CL images, most grains are weakly to moderately zoned and higher initial 87Sr/86Sr; 0.7059 and 0.7187. (Fig. 9A). Core and rim structures are rare. A total of 22 spot analyses The εNd (40 Ma) of eastern section rocks range from −1.1 to −2.3 were analyzed for this sample (Supplementary Document 5). The and for western rock varies between −0.43 and −1.6 (Supplementary zircons have variable, but mostly high U (584–2297 ppm) and Th

Document 4). Nd model ages (TDM; Depaolo, 1981) cluster tightly (356–4836 ppm) contents, resulting in high Th/U (0.26–1.9). Most around 0.80 to 0.92 Ga for eastern rocks and 0.71 to 0.91 Ga for western zircons have low common Pb content, with f206 (the proportion of 206 206 granitoids, suggesting that older continental crust or lithosphere was in- common Pb in total measured Pb) b1.0%, but some have f206 volved in generating the granitic magmas. up to 6.2% (Supplementary Document 5). 206Pb/238U ages range Considering the Sr and Nd isotope compositions of samples from from ~40 to 42.3 Ma (Supplementary Document 5). On an inverse both western and eastern sectors, most constitute a very coherent U–Pb concordia diagram (207Pb/206Pb vs. 238U/206Pb uncorrected group with small variations in the initial 143Nd/144Nd and 87Sr/86Sr for common 206Pb; Fig. 9A), most analyses are concordant within an- ratios, as expected in cogenetic magmas. There is only one exception alytical errors. The best analyses have weighted mean age of 41.9 ± (KR12-14; an aplitic dike), which is characterized by εNd (40 Ma) 0.3 Ma (MSWD = 0.88) (Fig. 9A), interpreted as reflecting the time values within the range of the other samples but with higher of zircon crystallization. 87Sr/86Sr (40 Ma) ratios. This situation is typical of rocks that have the same magmatic origin but were altered by fluids and/or with a 5.1.2. Sample KR12-10 (aplitic dike) strong continental crust signature. Since Nd and Sm are much less Zircons from sample KR12-10 are fine-grained, mostly b50 μmlong. mobile than Sr and Rb, only the Sr isotope signature is significantly In CL images, zircons are characterized by magmatic concentric zoning disturbed by alteration. Petrographic evidence shows that the aplitic (Fig. 9B). Fourteen analyses were conducted on zircons from this sam- dike sample shows no evidence of alteration and, as such, the most ple. The zircons have low to moderate (126–1312 ppm) U and Th likely explanation is that it crystallized from a melt with a much (90–1300 ppm) contents, with Th/U ratios between 0.7 and 1.8 (Sup- stronger upper crustal influence than most of the contemporaneous plementary Document 5). Common lead (f206) ranges from 0.28– magmas in the area. 3.97%, except point @05 with 55.68% f206. The higher f206 may be related On a 143Nd/144Nd vs. 87Sr/86Sr plot (Fig. 8), the Kashmar granit- to fractures in the zircons, possibly due to the atmosphere during mak- oids (and one dacitic lava) differ from older arc-related Sabzevar ing discs. The 206Pb/238Uand207Pb/206Pb (uncorrected for common Pb) magmatic rocks, which are dominated by depleted mantle inputs. define a discordia on the inverse (Terra-Wasserburg) U–Pb concordia The difference likely reflects the fact that Cadomian (Ediacaran– plot (Fig. 9B) with an intercept age of 40.13 ± 0.53 Ma (MSWD = Cambrian) Iranian lithosphere was significantly the source of 1.7). This is interpreted as the age of aplitic dike crystallization. Kashmar granitoids. 5.1.3. Sample KR12-15 (granodiorite) Zircons from this sample are fine-grained and show short prismatic and/or broken forms. Sixteen zircon grains with oscillatory zoning show 10 N-MORB Cadomian gneiss Th/U ratios of 0.57 to 1.3 and form a cluster with weighted mean ages of Cadomian granite 39.87 ± 0.47 Ma (MWSD = 1.01, Fig. 9C). Common lead is quite low, Kashmar granites 5 with f206 ranging from 0.15 to 2.9% (Supplementary Document 5). Chah Salar granite Some zircons show well-defined cores and one dated point (@17) has Sabzevar adakites an age of 647.2 Ma (Supplementary Document 5). We interpret this as Sabzevar ophiolite 0 a xenocryst, picked up from older crust in the region.

Nd (40 Ma) 5.1.4. Sample K12-9 (granodiorite) -5 We dated two zircon aggregates from this granodiorite. The ﬁrst contains broken, large prismatic zircons with oscillatory zoning. Thir- teen grains were analyzed with low to moderate U (68–781 ppm) and -10 Th (32–666 ppm) contents and Th/U (0.42–0.89) (Supplementary Doc-

ument 5). Common lead (f206) ranges from 0.9 to 11.5%, except point @3 206 238 207 206 with f206 = 15.1%. The Pb/ Uand Pb/ Pb (uncorrected for -15 common Pb) deﬁne a discordia on the inverse (Terra-Wasserburg) U– 0.69 0.70 0.71 0.72 0.73 0.74 0.75 Pb concordia plot (Fig. 9D) with an intercept age of 41.20 ± 0.45 Ma (MSWD = 1.2). The second aggregate comprises euhedral and long 87 86 ( Sr/ Sr)i prismatic zircon grains with rare core–mantle structure. Eighteen grains with oscillatory zoning show Th/U ratios of 0.36 to 1.2. Common lead Fig. 8. Initial εNd vs. 87Sr/86Sr for Kashmar magmatic rocks compared with Sabzevar mag- (f206) ranges from 0.8 to 11.4% (Supplementary Document 5). Com- matic belt rocks and Caomian crust of Iran. Data for Chah Salar arc granites, Sabzevar bined 206Pb/238Uand207Pb/206Pb ratios deﬁne a discordia on the inverse adakitic-like lavas and Biarjmand Cadomian granites from Shafaii Moghadam et al. (un- – published data) and Sabzevar ophiolites from Shafaii Moghadam et al. (2014). Data for (Terra-Wasserburg) U Pb concordia plot with an intercept age of Biarjmand gneissic rocks from Shafaii Moghadam et al. (2015). 40.48 ± 0.64 Ma (MSWD = 2.5) (Fig. 9E). H. Shafaii Moghadam et al. / Lithos 216–217 (2015) 118–135 127

5.1.5. Sample K12-29 (micro-granodioritic enclave) intercept age of 40.54 ± 0.40 Ma (MSWD = 1.6). This is interpreted Zircons from sample K12-29 are ﬁne-grained and broken. Eigh- as the best age of micro-granodioritic enclave crystallization. teen analyses were conducted on zircons from this sample. The zircons have low to high (197–2319 ppm) U and Th (106–2385 ppm) 5.2. Zircon Hf–Oisotopes contents with Th/U ratios between 0.5 and 1.5 (Supplementary Doc- ument 5). Common lead is variable with f206 ranging from 0.35 to 4.9, εHf(t) value for zircons from western and eastern belts are very sim- 206 238 except point @09 with 13.1% f206.Combined Pb/ Uand ilar. The εHf(t) values for western granitoid zircons range from +0.4 to 207 206 Pb/ Pb (uncorrected for common Pb) deﬁne a discordia on the +5.5(mean= +3.2) (Figs. 10Aand11A). TDM.1 age (single-stage Hf- inverse (Terra-Wasserburg) U–Pb concordia plot (Fig. 9F) with an isotope model age assuming that the sample was derived from depleted

A KR12-46 Intercepts at 0.10 41.09±0.30 Ma @7 MSWD=0.88 40.5 Ma

Pb 0.08 @8

206 @6 40.8 Ma

Pb/ 40.5 Ma 207 0.06

45 44 43 42 41 40 39 38 0.04 142 146 150 154 158 162 166 170

238U/206Pb

0.4 B KR12-10 Intercepts at @9 @11 40.13±0.53 Ma 38.9 Ma 41.7 Ma 0.3 MSWD=1.7 @12 @10 40.3 Ma 40.7 Ma Pb 0.2 206

Pb/ @8 207

0.1 39.7 Ma @13 40.1 Ma 70 60 50 40 0.0 80 100 120 140160 180 238U/206Pb

0.075 C Intercepts at KR12-15 39.87±0.47 Ma MSWD=1.01 40.1 Ma 0.065 @4 @6 40.5 Ma Pb @5

206 40.1 Ma 0.055 Pb/

207 39.4 Ma @7 0.045 43 42 41 40 39 38 37

0.035 146 150 154 158162 166 170 174 178

238U/206Pb

Fig. 9. U–Pb inverse concordia diagrams for zircons from the Kashmar western and eastern granitoids. 128 H. Shafaii Moghadam et al. / Lithos 216–217 (2015) 118–135

D Intercepts at 40.4 Ma 0.14 @10 41.20±0.45 Ma MSWD=1.2 0.12 K12-9 ﬁrst aggregate

0.10 Pb

206 @8 0.08 Pb/ 40.4 Ma 207

0.06 50 46 42 38

0.04 125 135 145 155 165 175 185 238U/206Pb

0.8 E Intercepts at 40.48±0.64 Ma 0.6 MSWD=2.5 K12-9 second aggregate 42.8 Ma

Pb @16 39.8 Ma 206 0.4 @17 Pb/ 207

0.2

140 100 60 300 0.0 20 60 100 140 180 238U/206Pb

0.18 F Intercepts at 40.54±0.40 Ma 0.16 MSWD=1.6 39.0 Ma K12-29 @8 0.14

Pb 0.12 206 @9 Pb/ 0.10 @7 39.1 Ma 207 38.8 Ma 0.08

0.06 48 464442 40 38 36 0.04 130 140 150 160 170 180 238U/206Pb

Fig. 9 (continued).

mantle) varies between 0.50 and 0.70 Ga whereas TDM.2 (two-stage Hf- +8.7‰ (except two points with +4.2 and +4.3‰) for western granit- isotope model age assuming that the sample was derived via melting of oids (Fig. 10C). the lower crust following derivation from depleted mantle) ranges between 0.62 and 0.88 Ga (Fig. 10B; Supplementary Document 6). The 6. Discussion δ18O values vary from +6.1 to +8.7‰ (except one analysis with +4.0‰)forwesterngranitoids(Fig. 10C). 6.1. Magma source and petrogenesis The εHf(t) values for the eastern granitoids range from −1.9 to

+7.2 (mean ~+2.3) (Fig. 10A). TDM.1 age varies between 0.47 and The Kashmar Eocene granitoids are I-type, subduction-related calc- 0.81 Ga whereas TDM.2 ranges between 0.54 and 1.00 Ga (Supplementa- alkaline igneous rocks with isotopic evidence showing mantle-derived ry Document 6). The δ18O values show large variations, from +6.3 to magmas interacted with older crust. They have variable, but often H. Shafaii Moghadam et al. / Lithos 216–217 (2015) 118–135 129

40 80 A B 30 60

20 40 Number Number 10 20

0 0 -2 0 2 4 6 8 500 600 700 800 900 1000 Hf (zircon) zircon Hf TDM2 model age

60 12 C D 45 9

30 6 Number 15 Number 3

0 0 456789 500 600 700 800 900 1000 18 O (zircon) Bulk rock Nd TDM

18 Fig. 10. Histograms of zircon εHf (A), Hf TDM. (B), zircon δ O (C) and bulk rock model ages (D) for the Kashmar granitoids.

high K2O(1–5.5 wt.%) and low CaO (0.5–5.6 wt.%) and Na2O (1.1– 1984). It can be seen from Figs. 8 and 11 that Kashmar granitoids con- 4.6 wt.%) contents similar to I-type granites, except dioritic sample tain a larger proportion of isotopically evolved crustal components KR12-22 with high CaO content (9.5 wt.%). Kashmar granitoids contain than older magmatic rocks in the region including Late Cretaceous–Pa- biotite and hornblende and vary from metaluminous to peraluminous, leocene Chah Salar granites (Fig. 2), Eocene Sabzevar adakitic-like lavas as expected for I-type granites (Chappell and White, 2001). Kashmar and Late Cretaceous Sabzevar ophiolitic rocks. granitoids as well as volcanic rocks have arc-like signatures (with In the zircon εHf vs. δ18O diagram, Kashmar granitoids differ from calc-alkaline afﬁnity) including Nb–Ta–Ti depletion and enrichment in S-type granite and are similar to I-type granites (Fig. 11B). The mean 18 Ba, Th, Rb, U, Pb and K, although HFSE depletions and LILE enrichments δ Ozircon value = 7.0 ± 0.8‰ is signiﬁcantly higher than that expect- are also the signatures of syn- to post-collisional rocks (Pearce et al., ed for zircons from mantle melts (~5.3‰; Eiler, 2001), indicating an

20 Hf 11 pm Depleted mantleAB/Hf S-type c=1.6 granite 10 0.5 Ga Cadomian crust 10 1 Ga 60% 9 lower crust 0 zircons 50% CHUR 8 1.85 Ga 40% Hf (t) -10 7 30% I-type granite Cadomian zircons (40 Ma) 6 20% Late Cretaceous Sabzevar granites

-20 O (zircon) (‰VSMOW)

18 5.3‰± 0.3‰ 10% Sabzevar 5 ophiolite gabbro -30 0 500 1000 1500 -15 -10 -5 0 5 10 15 Age (Ma) Hf (t)

2.0 12 C Depleted mantle= +16 D

1.5 8 Mantle input

1.0 4 Zircon crystallization Hf (t) Th/U

0.5 0 Crustal contamination

Cadomian crust= av.>-7 0 -4 -20246 0 0.02 0.04 0.06 0.08 0.10 0.12 0.14 Hf (t) Yb/Hf

Fig. 11. A — U–Pb age vs. εHf for zircons from the Kashmar granitoids. B — Plot of δ18OversusεHf(t) for Kashmar granitoids (Modiﬁed after, Huang et al. (2013); Kemp et al. (2007)), showing curves corresponding to magma evolution by crustal assimilation–crystallization (AFC). Hfpm/Hfc = ratio of Hf concentration in the parental magma (pm) to Hf concentration in crustal (c) rocks. C — Hf isotope composition of zircons from the Kashmar granitoids plotted against the Th/U ratio measured for same part of the crystal. D — Yb/Hf ratio vs. εHf diagram for Kashmar zircons to see magma addition and/or crustal assimilation effects. Data on the Sabzevar gabbro and granite zircons is from Shafaii Moghadam et al. (unpublished data) and on Cadomian granites is from Shafaii Moghadam et al. (2015). S-type granites (supracrustal zircon) has εHf = −12 and δ18O=10‰ (Li et al., 2007, 2009); and the lower crust zircon has εHf = −5.2 and δ18O = 9.4‰ (Li et al., 2010). For analytical methods of un-published data see Supplementary Document 7. 130 H. Shafaii Moghadam et al. / Lithos 216–217 (2015) 118–135

18O-enriched crustal component in the magma from which the zircon discrepancies between crystallization and bulk rock Nd and zircon Hf crystallized. Higher values (N7.5‰) are attributed to supracrustal model ages as well as inherited by zircon components (e.g., Altherr sources; either sedimentary rocks (δ18O=10–30‰)oralteredvolcanic et al., 1999; Altherr et al., 2000; Galan et al., 1996; Kemp et al., 2005a; 18 rocks (~20‰)(Valley and Lackey, 2005). The δ Ozircon of Kashmar Kemp et al., 2005b; Paquin and Altherr, 2002; Stevens and Clemens, granitoids can be explained by either addition of subducted fluids or 1993; Topuz et al., 2010). Interestingly, we found rare evidence of involvement of continental crust, or a combination of both processes, Cadomian zircons in the rocks we analyzed, suggesting that zircon crys- perhaps accompanied by fractional crystallization. tallization commenced before ingestion of supra-crustal (Cadomian) Assuming that AFC processes describe magmatic evolution for components and/or zircons were quite completely dissolved in the Kashmar granitoids (using εHf vs. δ18O for crustal and mantle zircons melt. end-members), the Kashmar zircons precipitated from a mostly juve- It is difficult to unequivocally identify the source of Cenozoic granit- nile melt containing 20–50% older crustal components (Fig. 11B). oids in Iran, both in the UDMA and in Alborz Magmatic Belt, and to cor- The observed oxygen isotopic composition of Kashmar granitoids relate these with NE Iran plutonism. Aghazadeh et al. (2010) concluded is consistent with an interpretation that these are I-type granitoids. that 29 Ma old granitoids in NW Iran were derived from a subducted 18 Caledonian I-type granites in Australia have δ Ozircon of 6–8.5‰ mélange that intruded into the supra-subduction mantle wedge in the (Kemp et al., 2009). For I-type granites, δ18Ovaluesofwholerocks form of “cold plumes”, a model suggested earlier by Gerya and Yuen fall into a range of 6–10‰, while δ18O values for zircons are 5–8‰ (2003) and Castro et al (2010). However, granitic melts produced (Li et al., 2007). from such MORB-sediment mélanges should be in equilibrium with re- Nd- and Hf-isotopic results also indicate involvement of an isoto- sidual garnet (Castro et al., 2010), consistent with the observation that pically evolved component, probably older continental crust. εNd these granites mostly have adakitic chemical signatures. This is not (40 Ma) of the Kashmar magmatic rocks varies between −0.4 and the case for Kashmar calc-alkaline granites, which show fractionation −2.3, significantly higher than for Cadomian gneisses and granites control by feldspar, not garnet. This different signature along with in central Iran at the same time (εNd; 40 Ma = −2.2 and −5.5 for higher εNd shows that the NW Iran granitoids originated from a differ- Cadomian gneissic rocks and −2.8 and −5.8 for Cadomian granites; ent source than Kashmar granitic rocks. Shafaii Moghadam et al., 2015 and Shafaii Moghadam et al., unpub- Our bulk rock Nd and zircon Hf and O isotopic studies of the lished data). Bulk rock Nd TDM.forKashmargranitesgive Kashmar granitoids indicate that these are not juvenile additions to Neoproterozoic model ages (Fig. 10D), similar to both the inherited the crust from the mantle, but represent mixtures of juvenile melt zircons from Kashmar pluton and to the U–Pb crystallization age of and older continental crust, probably Cadomian crust of Iran. It is Cadomian granites in central Iran (e.g., Shafaii Moghadam et al., widely accepted that I-type granitoids in orogenic belts result 2015; Ramezani and Tucker, 2003). Similar rocks outcrop just west when basaltic parent magmas interact with continental crust of the study area (Fig. 2), although this suspected Cadomian base- through either magma mixing, or assimilation combined with frac- ment has not yet been studied. tional crystallization (AFC) (e.g., Altunkaynak, 2007; Altunkaynak Zircon εHf for Kashmar granitoids varies between −1.9 and +7.2 et al., 2012; Dilek et al., 2009). A mantle component in the Kashmar (mean = +2.8 ± 1.6) higher than that of central Iranian Cadomian granitoids accords well with the “juvenile” character of the inferred gneisses at 40 Ma (~−10 to −2; Shafaii Moghadam et al., 2015,Shafaii low δ18O values in some zircons. These juvenile melts were subse- Moghadam et al., unpublished data). Most Kashmar granitoid zircons quently modified by crustal contamination as evidenced by the (N95%) have relatively low εHf values that can be explained as involve- spread of zircon εHf and δ18Ovalues(Fig. 11B). The higher zircon ment of older continental crust mixed with a juvenile component. δ18O values shift toward the Iran Cadomian zircons. Higher bulk rock εNd and zircon εHf of Kashmar granitoids compared To decipher the origin of the Kashmar granitoids we applied an AFC- to those of Cadomian crust reveal significant involvement of juvenile mixing model (Depaolo, 1981) based on bulk rock Nd–Sr isotopes, con- melts. Zircon εHf values for Kashmar granitoids also suggest that they sidering Sabzevar ophiolitic lava as representing juvenile mantle source could be partial melts of the amphibolites and/or metamorphosed and melt and average Cadomian upper and lower crust as assimilant lower crustal intermediate rocks (Zhao et al., 2013). Zircon Hf (TDM.2) (Fig. 12A). Our model shows that a mixture of 10–20% Cadomian model age ranges between 0.55 and 1.00 Ga (Fig. 10B), similar to ages lower crust and 80–90% juvenile mantle melt that fractionated ~4× as of Cadomian granites (~520–600 Ma) in central Iran. The relative varia- much of a low-P assemblage (Opx, Cpx, Amph, Biot, Plag, Ap and Ilm) tion of oxygen and hafnium isotope ratios in Kashmar zircons indicates as it assimilated could explain the isotopic composition of Kashmar that any mixing end-members were involved similarly for all rocks in magma (Fig. 12). the area. Uniform and almost-mantle-like isotopic compositions suggest that any mixing occurred deep in the crust and did not involve sed- 6.2. Temporal and spatial comparison of Kashmar granitoids with iments. Indeed, the Hf–O isotope arrays extend to mantle-like values Urumieh–Dokhtar magmatic rocks (central Iran) (and quite decouple from bulk rock Nd isotope), indicating that zircon crystallization commenced before ingestion of supra-crustal An important question concerning the evolution and genesis of the (Cadomian) components (Kemp et al., 2007). This process can also ex- Kashmar magmatic rocks is how are these related to similar age igneous plain the rarity of zircon inheritance in Kashmar granitoids. rocks of the UDMA? The big event in Eocene time in Iran was regional Variation in 176Hf/177Hf ratios of zircon grains can be reconciled by extension manifested by core complexes (Fig. 1)(Verdel et al., 2007; open system processes like as magma-mixing and/or assimilation. Zir- Kargaranbafghi et al., 2012). This was accompanied by widespread igne- con εHf against Th/U diagram show relative reduction in 176Hf/177Hf ous activity, best known from the UDMA of central Iran. Eocene ratio with decreasing Th/U ratio of zircon grains (Fig. C). This may magmatism in NE Iran may be the northeastern continuation of the show addition of an unradiogenic (continental crust-like) component UDMA. Eocene magmatic rocks occur both north and south of Sabzevar (Kemp et al., 2007). Crustal assimilation is also reconciled from εHf ophiolites (Fig. 1) but are more abundant in the south. The magmatic against Yb/Hf diagram (Fig. 11D). rocks of this belt vary from mafic to felsic and from tholeiitic to calc- Underplating of mafic magmas near the continental Moho can sup- alkaline, shoshonitic and even adakitic. Older granitoids with Late Creta- ply sufficient heat for partial melting of the lower crust (e.g., Hildreth, ceous to Paleocene U–Pb zircon ages (ca. 97 and 68–49 Ma; Shafaii 1981; although this mechanism is questioned by Castro and Gerya Moghadam et al., unpublished data) are widespread in the Arghash (2008) and Castro et al. (2010)). This can generate high-K calc- and Sheshtamad regions (Figs. 2 and 13). Younger plutonic and volcanic alkaline I-type granitoids that incorporate variable proportions of rocks (ca. 45–30 Ma; Shafaii Moghadam et al., unpublished data) with mantle- and crust-derived components, and can be identified by large adakitic and calc-alkaline characteristics are also common in this region. H. Shafaii Moghadam et al. / Lithos 216–217 (2015) 118–135 131

0.5132 15 Nain Oligocene volcanics Urumieh-Dokhtar Yeganehfar et al., 2013 A magmatic belt B Urumieh-Dokhtar MB 12 Kashmar granites (Chiu et al., 2013) Starting melt Sarjoughin et al., 2012 9 Sabzevar lava Urumieh-Dokhtar MB Honarmand et al., 2014 Sabzevar magmatic belt AFC trend NW Iran 6 0.5128 Mixing trend Aghazadeh et al., 2010 Number 3 Kashmar dikes 0 10% 0 20 40 60 80 100

Nd Age (Ma) 30% 144 0.5124 20% Kashmar 50%

Nd/ granitoids 10% 10% 70%

143 50% Average Cadomian upper crust Central Iran 30% 30% Eocene magmatic rocks 0.5120 Average Cadomian Sabzevar magmatic belt lower crust Eocene lavas r=0.2 Late Cretaceous-Paleocene Fractionating minerals: Opx (0.05) + Cpx (0.15) NW Iran + Amph (0.30) + Biot (0.10) + Plag (0.30) + Eocene lavas Ap (0.05) + Ilm (0.05) 0.5116

0.702 0.706 0.710 0.714 0.718 0.722

87Sr/86Sr

Fig. 12. Plot of 143Nd/144Nd vs. 87Sr/86Sr for the Kashmar magmatic rocks to model the formation of Kashmar granitoids (AFC model according to Ersoy (2013)). The composition of average Cadomian lower and upper crust is according to Shafaii Moghadam et al. (2015). Sabzevar lava composition is from Shafaii Moghadam et al. (2014). The Eocene central Iran (Urumieh– Dokhtar) magmatic rocks, Cretaceoues–Eocene Sabzevar lavas and NW Iran lavas are shown for comparison (data from Shafaii Moghadam et al., unpublished data). Insect ﬁgure is his- togram of magmatic rock age distribution in Urumieh–Dokhtar and Sabzevar magmatic belt. For analytical methods of un-published data see Supplementary Document 7.

Sabzevar adakites (Fig. 13) have Late Paleocene ages (ca. 58 Ma; wedge (Aghazadeh et al., 2010) and/or melting of a metasomatized lith- (Rossetti et al., 2014)). Further north, the Sabzevar magmatic belt in- ospheric mantle (Castro et al., 2013) respectively. cludes andesitic to dacitic domes with Ar–Ar and U–Pb ages of ca. 46– Our compiled age and isotopic data for UDMA igneous rocks (Figs. 12 48 Ma (Fig. 13; Shafaii Moghadam et al., unpublished data). Quchan and 13) and Sabzevar magmatic rocks including Kashmar granitoids re- adakitic lavas in the northern part of the Sabzevar ophiolites (Fig. 13) veal that there are no big differences between Eocene igneous rocks of have Plio-Quaternary ages and may have been formed by post- Iran. Although studies reporting both precise ages and Sr–Nd isotope collisional melting of a subducted slab and/or mafic thickened lower data are rare for UDMA rocks, available data confirm contributions of crust, triggered by asthenospheric rise after slab break-off or delamina- continental crust and mantle melts to form UDMA melts. tion (Shabanian et al., 2012). Similar to the UDMA of central Iran, Eocene time marked a peak of 6.3. A petrotecetic model for Paleogene subduction-related igneous rocks of magmatic activity in the Sabzevar magmatic belt (Fig. 12B; Verdel Iran et al., 2011; Chiu et al., 2013). There are three differences between UDMA and Sabzevar belt magmatism, including: 1) Oligocene Kashmar granitoids, dikes and volcanic rocks show calc-alkaline magmatism – common in the UDMA – is rare in the Sabzevar belt; characteristics linking them to post-collisional extension and collapse 2) Late Cretaceous–Early Paleocene (N68 Ma) magmatism – common after Sabzevar Ocean closure and core complex formation in central in the Sabzevar belt – is rare in the UDMA; and 3) Eocene magmatism Iran. Isotopic data indicate assimilation of Cadomian crust by mantle in central Iran is subduction-related but is post-collisional in the melts. An important additional constraint for the origin of the granitic Sabzevar belt as Paleocene time is when the Sabzevar basin closed. In rocks is their REE patterns (Fig. 7). The observed flat HREE patterns in- addition, there is no mineralization in Kashmar granitoids, but mineral- dicate no residual or fractionating garnet, and the slight rise from Dy ization occurs in Sabzevar Paleocene–Eocene adakitic intrusions and is to Lu suggest amphibole fractionation. The presence of slight to signifi- widespread elsewhere in the UDMA. cant negative Eu anomalies indicates that fractionation of feldspar and/ Kashmar granitoids and UDMA igneous rocks are isotopically similar or residual feldspar also played an important role in petrogenesis. The (Fig. 12 A). Compared to Kashmar granites, Eocene igneous rocks from arc-like features of the Kashmar granitoids (such as Nb–Ta depletion the northwestern and central UDMA have a stronger mantle signature relative to LREEs) along with their isotopic characteristics are consistent with less input of Cadomian crust (Fig. 12A). However, Eocene lavas with their I-type signatures. The Kashmar batholith might have been from Sabzevar magmatic belt also have higher mantle contribution. derived by underplating of mafic magmas beneath Cadomian lower Moreover, Eocene granitoids from the central UDMA (Kuh-e-Dom; continental crust after the Sabzevar Ocean closure along the Eurasian Sarjoughian et al., 2012) show a higher contribution of Cadomian continental margin. The dominant input of juvenile mantle-derived crust (Fig. 12 A; N60%). Early Eocene to Middle Miocene Kashan granit- magmas may have been associated with extension above Tethyan sub- oids show variable isotopic ratios, and Honarmand et al. (2014) con- duction zone along the Zagros suture zone during Eocene time. cluded that these melts involved ∼60–70% of a lower crust-derived Petrogenetic models for Kashmar igneous rocks must be consistent melt and ∼30–40% melt from subcontinental lithospheric mantle. Oligo- with our understanding of Iran as a Cenozoic active plate margin. cene lavas from Nain area (UDMA) also show interaction of mantle Kashmar igneous rocks reflect this thermal reworking of Iranian melts with upper Cadomian crust (Yeganehfar et al., 2013). The Oligo- continental crust and it is clear that they are related to the UDMA and Miocene (ca. 29 Ma) adakitic and Late Eocene shoshonitic (ca. 38 Ma) reflect post-collisional magmatism after the Sabzevar Ocean closure. granitoids from northwestern UDMA may show different source, During Late Cretaceous–Early Paleocene time, continuous convergence resulting from melting of a subducted mélange within the mantle between Arabia and Iran helped close the Sabzevar basin, emplacing 132 H. Shafaii Moghadam et al. / Lithos 216–217 (2015) 118–135

Khoy Caspian Sea

Transect Quchan 7 Urumieh-Dokhtar Magmatic Belt 6 5 Torud Sabzevar 4 Sanandaj-Sirjan Zone Arghash Tehran

1 2 Kashmar Kashan 3

Dorouneh Fault

adakites B U-Pb zircon 20 Chiu et al., 2013

dike Extension, core complex formation granitoid and magmatism in central-NE Iran 40

calc-alkaline granitoid andesites & dacites 60 early tholeiitic to Verdel et al., 2011 late calc-alkaline Rossetti et al.,

Age (Ma) & adakitic granitoids (2014) & lavas No geochem. 80 Sabzevar ocean formation data and subduction Recycled crust Juvenile crust

Arghash old Ar-Ar dating 100 granites Juvenile crust Recycled crust

1 2 3 4 5 6 U-Pb dating 120 Torud Quchan Kashmar Sabzevar adakites Sabzevar volcanics Arghash- Chah Salar Central Iran volcanics

Fig. 13. Simpliﬁed chart (B) showing the age distribution of magmatic rocks in central Iran and Sabzevar magmatic belt along transect shown in (A).

Sabzevar and other central Iranian ophiolites accompanying transition complexes have been documented to date (Fig. 1) but there are proba- of the SW Eurasia from an advancing (extensional) to a retreating (com- bly many more. pressional) convergent plate margin (e.g., Agard et al., 2011; Rossetti Verdel et al. (2011) identified three major phases of Paleogene vol- et al., 2014). Iran compression including Sabzevar basin closure was canism in central Iran including; (1) latest Paleocene–Early Eocene followed by orogenic collapse during Eocene. Eocene extension and lith- phase of pre-extensional arc magmatism; (2) Middle-Eocene extension ospheric thinning may have been accompanied decompression melting with high volcanic output; and (3) limited, latest Eocene–Early Oligo- of upwelling hydrous asthenosphere (Verdel et al., 2007, 2011). Eocene cene, late- to post-extensional volcanism with back-arc basin geochem- extension may also have been accompanied by lithospheric delamina- ical affinity. Eocene Kashmar magmatic rocks as well as other Eocene– tion, further stimulating extension and rapid exhumation of the central Oligocene Sabzevar igneous rocks correspond to the second and third Iranian core complexes. magmatic phases and thus show a clear link to the Urumieh–Dokhtar Recent studies (Chiu et al., 2013) show that UDMA volcanism was magmatism. Break-off of subducted continent-ocean transitional litho- especially widespread from Eocene to Oligocene time (55–25 Ma). sphere beneath the Zagros Mountains (e.g., Molinaro et al., 2005)and/ Calc-alkaline magmatism dominated during this ~30 m.y. time period or lithospheric thickening with partial delamination to the northeast (Chiu et al., 2013). The Eocene–Oligocene magmatic peak is described of the Zagros (e.g., Hatzfeld and Molnar, 2010)ismechanismssuggested as a magmatic “flare-up” (Verdel et al., 2011). Magmatic flare‐ups are to have caused Cenozoic–Quaternary volcanism throughout Iran. Al- common in extensional settings above a subduction zone and/or in though Late Cretaceous–Paleocene arc-like magmatic rocks (with juve- post-collisional settings. The Iran Eocene magmatic flare‐up was broad- nile signature) may reflect early UDMA plutonism, they also may have ly coincident with metamorphic core complex formation in Central Iran been generated by subduction of Sabzevar oceanic lithosphere, not Ara- (Karagaranbafghi et al., 2012; Verdel et al., 2007). Four Eocene core- bian plate subduction as is responsible for most UDMA magmatism. This H. Shafaii Moghadam et al. / Lithos 216–217 (2015) 118–135 133

A) Late Cretaceous-Early Paleocene Sabzevar subduction

SW high-P central Iran NE blueschists Back-arc magmatism arc volcanism Neotethys Turan plate subduction

Sabzevar ophiolite

B) Early to Late Eocene core complex exhumation and magmatism Sabzevar Kashmar suture granitoids metamorphic UDMA core complex

Cadomian crust

AFC zone

Fig. 14. Schematic model for the formation and evolution of Sabzevar magmatic belt including Kashmar granitoids (modified after Rossetti et al. (2014)). scenario could also explain the genesis of Paleocene (ca. 58 Ma) adakites 5- More precise age and isotopic data (including both bulk rock Sr–Nd intruding Sabzevar ophiolites (Rossetti et al., 2014) in a post-orogenic and zircon Hf–O isotopes) are needed to better compare and under- setting, which demonstrates that partial melting of the subducting stand relationships between UDMA and Kashmar magmatic rocks, Sabzevar Ocean occurred up to at least Late Paleocene time. Fig. 14 sche- including relationships between plutonic and volcanic rocks, and matically illustrates the possible evolutionary scenario for forming the the relationship between UDMA and Kashmar igneous rocks, exten- Sabzevar magmatic belt. The Sabzevar Ocean was open between sion, and mineralization. the Lut block to the south and the Turan block to the north from at least middle Cretaceous time. Intraoceanic subduction within the Supplementary data to this article can be found online at http://dx. Sabzevar basin began at least before Albian time as testified by the age doi.org/10.1016/j.lithos.2014.12.012. of felsic segregations within Sabzevar high-pressure rocks (Rossetti et al., 2010). Intraoceanic subduction during Late Cretaceous, as evi- Acknowledgments denced by the age of ophiolitic plagiogranites (ca. 100–78 Ma; Shafaii Moghadam et al., 2014) may have been responsible for generating the This research was supported by the “Strategic Priority Research SSZ-type ophiolitic lavas and plutonic rocks, although the Sabzevar Program (B)” of the Chinese Academy of Sciences (grant no. Ocean could have opened as a backarc basin. Late Cretaceous intra- XDB03010800) to XHL and the State Key Laboratory of Lithospheric oceanic subduction could also be considered the mechanism for forming Evolution, IGG-CAS to HSM. We are very grateful to Antonio Castro fi an arc within the Sabzevar basin, testi ed by the Arghash-Chah Salar old and A. Dokuz for their constructive reviews of the manuscript. Edito- – – granites (ca. 97 60 Ma). Similar to UDMA magmatic rocks, the Eocene rial suggestions by Nelson Eby are appreciated. All logistical supports Oligocene Sabzevar magmatic rocks formed during Eocene extension. during field studies came from Damghan University.

7. Conclusions References

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