Post-Eocene volcanics of the Abazar district, Qazvin, Iran: Mineralogical and geochemical evidence for a complex magmatic evolution

Journal of Asian Earth Sciences 45 (2012) 79–94

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Journal of Asian Earth Sciences

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Post-Eocene volcanics of the Abazar district, Qazvin, Iran: Mineralogicaland geochemical evidence for a complex magmatic evolution

A. Asiabanha a,⇑, J.M. Bardintzeff b,c, A. Kananian d, G. Rahimi d

a Department of Geology, Faculty of Science, Imam Khomeini International University, Qazvin, Iranb IUFM, Université de Cergy-Pontoise, 95000 Cergy-Pontoise, Francec Laboratoire de Pétrographie-Volcanologie and équipe Planétologie, UMR CNRS IDES 8148, Bât. 504, Université Paris-Sud, 91405 Orsay Cédex, Franced Department of Geology College of Sciences, University of Tehran, Tehran, Iran

a r t i c l e i n f o a b s t r a c t

Article history:Received 2 July 2010Received in revised form 6 September 2011Accepted 17 September 2011Available online 20 November 2011

Keywords:AlborzIranEruptive styleMagma minglingContinental arc

1367-9120/$ - see front matter � 2011 Elsevier Ltd. Adoi:10.1016/j.jseaes.2011.09.020

⇑ Corresponding author. Tel.: +98 281 8371365; faxE-mail addresses: [email protected] (A. Asiabanh

u-psud.fr (J.M. Bardintzeff), [email protected] (G. Rahimi).

The style of volcanism of post-Eocene volcanism in the Alborz zone of northern Iran is different to that ofEocene volcanism (Karaj Formation). Indeed, the volcanic succession of the Abazar district, located in anarrow volcanic strip within the Alborz magmatic assemblage, is characterized by distinct mineralogicaland chemical compositions linked to a complex magmatic evolution. The succession was produced byexplosive eruptions followed by effusive eruptions. Two main volcanic events are recognized: (1) a thinrhyolitic ignimbritic sheet underlain by a thicker lithic breccia, and (2) lava flows including shoshonite,latite, and andesite that overlie the first event across a reddish soil horizon.

Plagioclase in shoshonite (An48–92) shows normal zoning, whereas plagioclase in latite and andesite(An48–75) has a similar composition but shows reverse and oscillatory zoning. QUILF temperature calcu-lations for shoshonites and andesites yield temperatures of 1035 �C and 1029 �C, respectively. The geo-thermometers proposed by Ridolfi et al. (2010) and Holland and Blundy (1994) yield temperatures of960 �C and 944 �C for latitic lava, respectively.

The samples of volcanic rock show a typical geochemical signature of the continental arc regime, butthe andesites clearly differ from the shoshonites, the latites and the rhyolites. The mineralogical andchemical characteristics of these rocks are explained by the following petrogenesis: (1) intrusion of ahot, mantle-depth mafic (shoshonitic) magma, which differentiated in the magma chamber to producea latitic and then a rhyolitic liquid; (2) rhyolitic ignimbritic eruptions from the top of the magma cham-ber, following by shoshonitic and then latitic extrusions; (3) magma mingling between the latitic andandesitic magmas, as indicated by the occurrence of andesite clasts within the latite; and (4) andesiticeffusions.

The youngest volcanic events in the Alborz zone show a close chemical relationship with continentalarc rocks, indicating that they formed in a continental collision setting.

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1. Introduction

The volcano-plutonic complex of the Alborz Ranges in NorthIran has been interpreted to represent the subduction of Neo-Tethyan oceanic lithosphere beneath the Central Iranian continen-tal microplate and the subsequent continental collision of theArabian and Iranian microplates in the Late Cretaceous-early Ceno-zoic (e.g., Alavi, 1994; Berberian and Berberian, 1981; Berberianet al., 1982; Golonka, 2004). Although magmatism in the two dom-inant volcanic zones in Iran (the Urumieh-Dokhtar in SouthwestIran and the Alborz in North Iran) started in the Early Cretaceous,

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the most voluminous magmatism occurred during the Eocene (Ala-vi, 1994). Younger (post-Eocene) magmatism, which has continueduntil the present, has a different style of volcanism but a similargeochemical signature compared with the Eocene magmatism.The Eocene volcanic succession in the Alborz magmatic assem-blage has been studied previously (e.g., Dedual, 1967; Annellset al., 1975; Ebrahimi, 2000; Asiabanha et al., 2009), whereas thecharacteristics of the post-Eocene volcanics are poorly known be-cause of sparse outcrop and uncertainties regarding age relations.Therefore, the aim of this study is to describe the petrologicaloccurrence of post-Eocene magmatic events of the Alborz zone inthe framework of regional tectonics and to compare these rockswith Eocene lavas, in order to obtain a better understanding ofthe complex geological evolution of the Alborz zone.

Asiabanha et al. (2009) divided the Eocene volcanic complex atAlborz (the Karaj Formation) into two main facies: (1) An earlier

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80 A. Asiabanha et al. / Journal of Asian Earth Sciences 45 (2012) 79–94

volcano-sedimentary facies composed of pyroclastic and epiclasticdeposits formed by subaqueous eruptions in a shallow sedimen-tary basin during the Early–Middle Eocene. The basin was then up-lifted and overprinted by orogenic movements that produced tightfolds and thrust faults. Evaporites were deposited in the uppermostpart of the volcaniclastic series. (2) Subsequently, mafic–felsic sub-aerial lava flows were produced with potassic calcalkaline to shos-honitic affinities, related to a continental arc regime.

Sporadic subaerial volcanism continued after the Paleogene(Berberian and Berberian, 1981), either as central volcanoes (e.g.,the Damavand, Sahand, and Sabalan mountains) or as fissure erup-tions. The appearance of these younger volcanic rocks is differentto that of Eocene volcanism. An understanding of the volcanicstyles and geochemical signatures of these rocks would be impor-tant in characterizing the geotectonic setting after continental col-lision in Iran.

The Abazar district, which is the focus of this study, is situatedin the western part of the Alborz zone. It is a post-Eocene volcanicprovince, associated with Eocene volcanic rocks, which appears tohave been produced by fissure eruptions, and is distinct from coex-isting rocks. Two different groups of volcanic facies (Eocene andpost-Eocene) are juxtaposed along a thrust fault (the North QazvinFault). The rocks of the facies are generally fresh and unaltered.This study aims to understand the volcanic and petrogenetic evo-lution of post-Eocene volcanic rocks in relation to the tectonic set-ting, in comparison with the older Eocene volcanic succession,based on facies analyses, mineral chemistry, and major and traceelement geochemistry. A tentative magmatic model is proposedto explain the coexistence of several distinct lava types in a smallgeographic area.

2. Volcanostratigraphy

The studied volcanic succession, within the Alborz magmaticassemblage (Fig. 1), records a maximum in volcanic activity duringthe Paleogene, which continued sporadically until the Miocene.The characteristics of the volcanic units and their succession indi-cate that they were produced by post-Eocene magmatism. The re-sults of field surveys, combined with a comparison of the studiedrocks with Eocene volcanics in the northern terrain, indicate thattwo distinct successions (Eocene and post-Eocene) are juxtaposedacross a thrust fault (Fig. 1). Consequently, the volcanic deposits ofthe study area are divided into an Eocene volcanic succession andpost-Eocene subaerial volcanic deposits (Fig. 2), which are de-scribed in detail below.

2.1. Eocene volcanic succession

Asiabanha et al. (2009) divided the Eocene volcanics in thenorthern terrain into two main facies. The first is a volcaniclasticfacies (total thickness, 300–400 m) that is subdivided into twosubfacies: pyroclastic green tuffs (PGTs) in the lower part and epi-clastic variously colored tuffs and tuffaceous deposits (EVTs) in theupper part. The features of this facies, such as layering, graded bed-ding, trace fossils, convolute laminations, flute casts, numerousslumps, and microfossils, indicate a formation by explosive erup-tions in a shallow-marine sedimentary basin (Asiabanha et al.,2009; Lasemi, 1992). Moreover, Alavi (1995) proposed that theserocks were deposited in a trench–continental rise environment atthe foot of a continental slope, in front of an active magmaticarc. The second facies comprises mafic–intermediate and locallyfelsic lava flows that overlie inclined and locally folded pyroclasticdeposits. These observations indicate that uplifting and folding ofthe volcano-sedimentary basin occurred within a compressive re-gime, probably during the Pyrenean orogeny.

2.2. Post-Eocene subaerial volcanic deposits

The post-Eocene subaerial volcanic facies (thickness, �200 m)overlies the Eocene green pyroclastics and is subdivided into threesubfacies: (a) a rhyolitic ignimbritic sheet, (b) shoshonitic lavaflows, and (c) latitic–andesitic lava flows, which are described indetail below. Rock types are named according to the classificationproposed by Le Maitre et al. (1989, 2002). The strike-slip move-ment upon two parallel faults (the North Qazvin and Vers Thrustfaults) may have played an important role in creating pathwaysfor the ascending magma (Fig. 1).

2.2.1. Rhyolitic ignimbritic sheetThe thin rhyolitic ignimbritic sheet consists of an extensive

light-gray rhyolitic ignimbrite underlain by a buff- to pink-coloredlithic breccia flow (�50 m in thickness), and is exposed throughoutthe study area (Fig. 3a). The sheet is characterized by its light color,low density, and microphenocrysts of biotite in a gray hyaline ma-trix. The upper part of the ignimbritic sheet subfacies is a reddish,erosional soil-bearing surface; thus, the rock was transformed intoreddish soil by the thermal effects of later hot, mafic lava flows.

2.2.2. Shoshonitic and basaltic lava flowsThe reddish soil at the top of the ignimbritic sheet is covered by

shoshonitic lava flows along with scarce thick, gray to black basalt(which is not analyzed in this study) with columnar joints andshoshonite with massive to stratified structures and diopsidemegacrysts (Fig. 3b).

2.2.3. Latitic and andesitic lava flowsLatite (Fig. 3c) and andesite, found in the northern and eastern

parts of the study area, are more abundant than the mafic lavas. Inhand samples, these rocks are characterized by aphanitic and hya-line textures. The occurrence of andesites as rounded clasts in thelatitic host rock (Fig. 3d) indicates magma mingling. The occur-rence in the andesitic lavas of abundant well-rounded clasts (1–50 cm in size) resembling volcanic bombs and intercalated scoria-ceous lenses (1–2 m thick) indicates that the effusive stage wasinterrupted by sporadic parasitic explosions.

3. Petrography and mineralogy

The textural and mineralogical relations between volcanic fa-cies represent an important tool in identifying the eruption styleand petrological processes recorded by volcanic phases. In thepresent study, the occurrence of the flow lithic breccia as a base-ground facies is indicated by the presence of abundant volcaniclithic clasts and crystal fragments of quartz, plagioclase, and biotitein a trachytic groundmass. The overlying ignimbrite sheet containsa small proportion of crystals and lithic fragments, and a large pro-portion of shards and clasts (Fig. 4a). The ignimbritic sheet subfa-cies contain crystals of sanidine, biotite, quartz, plagioclase, andminor augite in an autaxitic and weakly welded groundmass thatcontains volcanic shards. Accordingly, these two units are inter-preted to represent the products of a gas-rich explosive siliciceruption that opened the vent explosively and then triggered theeruption of gas-rich lava.

The lava flows produced during the effusive stage (Fig. 2) in-clude shoshonite, latite, and andesite. The shoshonitic rocks con-tain microphenocrysts of zoned plagioclase, zoned diopside(Fig. 4b), olivine, and iddingsite (after pyroxene and olivine) in amicrolitic groundmass of the same mineral species along with opa-que minerals. In the shoshonites, phenocrysts of magnesiohasting-site are partly to completely oxidized or dehydrated, indicatingdehydration during rapid ascent of the magma (Buckley et al.,

Fig. 1. Upper right: Simplified structural map of Iran (redrawn after Alavi, 1991) showing the location of the study area. PTC–CCS: Paleo-Tethyan continent–continentcollisional suture; NTA–ACS: Neo-Tethyan arc–arc collisional suture; NTC–ACS: Neo-Tethyan continent–arc collisional suture. Centre: Geological map of the Abazar district,Iran.

Fig. 2. Stratigraphic column of volcanic units of the Abazar district, Iran.

A. Asiabanha et al. / Journal of Asian Earth Sciences 45 (2012) 79–94 81

Fig. 3. Field photographs of volcanic units of the Abazar district. (a) Rhyolitic ignimbritic sheet (Ig) underlain by lithic breccia (Lb) and overlain in turn by a shoshonitic lavaflow (Tb). (b) Shoshonite containing megacrysts of augite. (c) Flow folding in latitic lava. (d) Rounded clasts of andesite in latitic host rock, indicating magma mingling.

Fig. 4. Microphotographs of volcanic units. (a) Welded rhyolitic ignimbrite with numerous cuspate shards and fragmented biotite and quartz crystals. (b) Large, octahedral,zoned diopside in trachybasalt. (c and d) Phenocrysts of magnesiohastingsite with magnetite reaction rims in a trachytic groundmass. Note that the crystal in (c) was affectedby corrosion prior to oxidation. (a, plane polarized light; b–d, cross polarized light).


2006; Winter, 2001). The occurrence of disequilibrium conditionsduring eruption is indicated by zoning in plagioclase and augite,sieve texture in plagioclase, and the iddingsitization of olivineand pyroxene.

The intermediate lavas (latite and andesite) contain pheno-crysts of plagioclase, augite, diopside, sanidine, biotite, and magne-siohastingsite (Fig. 4c and d). As in the shoshonite, the phenocrystsin intermediate lavas are zoned, corroded, contain sieve textures,


and show evidence of oxidation/dehydration (Fig. 4d). However,most crystals in andesite have rounded and corroded margins,and sieve texture is evident in plagioclase.

Minerals within the lavas were analyzed with a CAMECA SX 100(15 kV, 10 nA) electron microprobe at Université Pierre et MarieCurie, Paris VI, France. Ka lines were used. Standards were alsoanalyzed, including diopside for Si, Ca, and Mg, Fe2O3 for Fe,MnTiO3 for Ti and Mn, Cr2O3 for Cr, albite for Na, and orthoclasefor K and Al. Count times were 10 s for both peaks and background,with a 5 lm defocused beam.

3.1. Plagioclase

The chemical compositions of plagioclase phenocrysts in thethree types of volcanic lava flows (shoshonite, latite, and andesite)are listed in Table 1, and are plotted on a compositional ternarydiagram (Fig. 5a). The composition of plagioclase in shoshonite isAn44–92 (mean value of An83, bytownite), whereas plagioclase in la-tite is An48–75 (mainly labradorite with some bytownite; mean va-lue of An61, labradorite), and plagioclase in andesite is An55–72

(mean value of An63, labradorite). Plagioclase in the shoshoniteshows normal zoning, whereas plagioclase in the latite and andes-ite shows reverse and oscillatory zoning (Table 1). Microlites in theanalyzed samples are K-feldspar.

Table 1Chemical compositions of selected plagioclase grains from samples of shoshonite (S4R4, R3on eight oxygens.

Sample S4R4 R37

Analysis 114(c) 116(m) 117(r) 86 94 95 9

SiO2 45.39 49.04 50.93 52.03 47.41 46.56 4Al2O3 34.30 32.42 30.87 30.01 32.96 33.18 3Fe2O3 0.44 0.46 1.26 0.85 0.64 0.76 0CaO 18.32 15.73 14.26 12.93 16.35 16.69 1Na2O 0.80 2.24 3.13 3.73 1.92 1.81 2K2O 0.05 0.18 0.33 0.26 0.13 0.12 0

Total 99.30 100.07 100.78 99.81 99.41 99.12 9Si 2.105 2.238 2.305 2.366 2.187 2.160 2Al 1.875 1.744 1.647 1.609 1.792 1.814 1Fe3 0.015 0.016 0.043 0.029 0.022 0.027 0Ca 0.910 0.769 0.692 0.630 0.808 0.830 0Na 0.072 0.198 0.275 0.329 0.172 0.163 0K 0.003 0.010 0.019 0.015 0.008 0.007 0

Total 4.983 4.985 4.993 4.990 4.998 5.005 5%Or 0.30 1.02 1.93 1.54 0.81 0.70 0%Ab 7.31 20.27 27.89 33.78 17.41 16.30 1%An 92.39 78.71 70.18 64.68 81.78 83.00 7

S6R8 R36 S6R5

139 147 92(c) 95(m) 96(r) 137(c) 1

SiO2 53.01 50.33 55.29 52.77 51.54 55.69 5Al2O3 29.07 30.95 27.88 29.33 30.17 27.78 2Fe2O3 0.47 0.49 0.50 0.52 0.81 0.58 0CaO 11.51 13.87 10.66 12.27 13.31 10.47 9Na2O 4.63 3.25 5.00 4.21 3.66 5.11 5K2O 0.24 0.18 0.34 0.26 0.22 0.36 0

Total 98.93 99.07 99.67 99.36 99.71 99.99 1Si 2.420 2.310 2.496 2.404 2.350 2.508 2Al 1.564 1.674 1.483 1.575 1.621 1.474 1Fe3 0.016 0.017 0.017 0.018 0.028 0.020 0Ca 0.563 0.682 0.516 0.599 0.650 0.505 0Na 0.410 0.289 0.438 0.372 0.324 0.446 0K 0.014 0.011 0.020 0.015 0.013 0.021 0

Total 5.001 4.993 4.979 4.992 4.994 4.979 4%Or 1.42 1.12 2.05 1.52 1.32 2.16 2%Ab 41.54 29.43 44.97 37.73 32.83 45.88 5%An 57.04 69.45 52.98 60.75 65.86 51.95 4

c = core; m = middle; r = rim.

Fig. 5b shows a variation diagram of Ca/Na ratio in plagioclasephenocrysts vs. the same ratio in the host rock. The shaded areashows the experimentally determined field of plagioclase–meltequilibrated under various pressures and H2O contents (data com-piled by Mashima, 2004). Although plagioclase phenocrysts in allrocks are equilibrated with their melts, it is clear that the andesitesand latites, which have contrasting mineralogical and chemicalcharacteristics, contain plagioclases with similar Ca/Na values. Thisfinding indicates similar thermal equilibration of the two magmasduring mingling in a convective magma chamber.

3.2. Pyroxene

Chemical analyses of pyroxenes (Table 2) reveal that the shosh-onite and andesite contain both diopside–augite and clinoenstatite,whereas the latite contains diopside–augite only (Fig. 6a). Analyses15 and 16 in shoshonite (Table 2) reveal high Ca contents (Wo 51.1and 50.3), characteristic of fassaite (Deer et al., 1978; Wandji et al.,2000). Some pyroxene crystals contain up to 12 mol% CaFe2SiO6

and 16 mol% CaAl2SiO6. The analyzed pyroxenes contain a widerange of Al contents (1.8–6.9 wt% Al2O3). Ti contents are low(0.3–1.3 wt%), as typically observed in convergent plate settings.The Cr2O3 content of both clinopyroxenes and orthopyroxenes isless than 0.3 wt%. Although some pyroxene grains are visually

7), latite (S6R8, R36, S6R5), and andesite (S8BR1). Compositions were calculated based

8 101 102 108 114 115 128

7.42 56.42 52.12 52.71 47.50 46.43 56.572.45 26.49 29.46 29.87 33.31 33.78 26.35.76 1.02 0.90 0.96 0.69 0.62 0.756.29 8.93 12.29 12.62 16.39 17.18 8.76.20 5.81 4.13 4.05 1.92 1.59 5.64.12 0.61 0.31 0.30 0.07 0.07 0.95

9.24 99.28 99.21 100.51 99.88 99.67 99.02.195 2.555 2.383 2.379 2.181 2.143 2.567.770 1.414 1.587 1.589 1.803 1.837 1.409.026 0.035 0.031 0.033 0.024 0.022 0.026.808 0.433 0.602 0.610 0.806 0.849 0.426.197 0.510 0.366 0.354 0.171 0.142 0.496.007 0.035 0.018 0.017 0.004 0.004 0.055

.014 4.992 4.999 4.997 5.002 5.000 4.993

.69 3.58 1.83 1.73 0.41 0.40 5.639.47 52.15 37.12 36.09 17.43 14.27 50.779.84 44.27 61.05 62.18 82.16 85.33 43.60

S8BR1

38(m) 140(r) 147(c) 153(m) 33(c) 34(m) 39(r)

7.33 51.94 53.37 51.16 54.12 53.39 53.126.81 30.50 29.11 30.77 28.92 28.94 29.29.60 0.91 0.61 0.70 0.77 0.99 0.73.41 13.45 12.09 14.12 12.20 12.43 12.84.78 3.28 4.27 3.17 4.49 4.36 4.33.44 0.17 0.24 0.16 0.48 0.41 0.41

00.37 100.25 99.69 100.08 100.98 100.52 100.72.565 2.351 2.421 2.326 2.429 2.412 2.397.414 1.627 1.557 1.648 1.530 1.541 1.558.020 0.031 0.021 0.024 0.026 0.034 0.025.451 0.652 0.588 0.688 0.587 0.602 0.621.501 0.288 0.376 0.279 0.391 0.382 0.379.025 0.010 0.014 0.009 0.027 0.024 0.024

.983 4.967 4.982 4.980 4.999 5.004 5.012

.56 1.05 1.43 0.92 2.69 2.38 2.341.28 30.32 38.45 28.59 38.91 37.90 37.016.16 68.63 60.12 70.49 58.41 59.72 60.64

Fig. 5. (a) Chemical compositions of feldspars in the volcanic rocks of the study areaplotted in an Or–Ab–An ternary diagram. (b) Relationships between Ca/Na molarratios in plagioclase phenocrysts and in whole-rock samples. The shaded areashows the experimentally determined field in which a melt equilibrates withplagioclase at variable pressures and H2O contents (adapted from Mashima, 2004).


zoned, no chemical zoning is apparent. The lack of zonation mayindicate that pyroxene was in equilibrium with the melt prior toeruption. Furthermore, the pyroxenes have high values of Mg#(average value for shoshonite, 0.84; average value for latite, 0.79).

A strong linear relation between Na + AlIV and AlIV + 2Ti + Cr(Schweitzer et al., 1979) above the line of Fe+3 = 0 (Fig. 6b) suggeststhat the pyroxenes in the mafic and intermediate lavas have a com-mon genesis, and that the eruptions occurred under conditions ofhigh oxygen fugacity. The analyzed pyroxenes plot in the orogenicarc field in a Ti + Cr vs. Ca diagram (Leterrier et al., 1982) (Fig. 6c). Ageothermometry analysis using the QUILF program (Andersenet al., 1993), based on two pyroxenes, yields equilibration temper-atures of 1035 �C and 1029 �C for shoshonitic and andesitic mag-mas, respectively. Although the pressure dependence of thegeothermometers is minor, we assume 270 MPa for shoshoniteand 130 MPa for andesite, based on the P–T phase diagram pro-posed by Rutherford and Devine (2003).

3.3. Amphibole

Microphenocrysts of amphibole occur mainly in the latite andandesite, and to a lesser degree in the shoshonite; their chemicalcompositions are listed in Table 3. Based on the findings ofðCaþNaÞ ¼ 2:45, Na ¼ 0:66, Na ¼ 1:79, ðNaþ KÞ ¼ 0:82, and

Ti ¼ 0:27, the amphiboles are compositionally magnesio-hasting-site to magnesio-hastingsitic hornblende (Leake, 1978; Leakeet al., 1997) (Fig. 7). According to Leake et al. (1997), such magmaticamphiboles are generally found in orogenic belts.

The presence of Mg-hastingsite phenocrysts indicates high vol-atile pressure within a closed system (Viccaro et al., 2006) in whichvigorous convection and mixing occur and the pre-existing miner-als, including clinopyroxene and olivine, react with melt to formamphibole (Foden and Green, 1992). The geothermometers pro-posed by Ridolfi et al. (2010) and Holland and Blundy (1994), basedon hornblende and plagioclase–hornblende compositions, yieldtemperatures of 964 �C and 944 �C for latitic lava, respectively.

The dehydration rims surrounding amphibole phenocrysts arerelated to decompression and consequent volatile loss immedi-ately preceding and during the eruption (Bardintzeff and Bonin,1987; Buckley et al., 2006; Viccaro et al., 2006).

3.4. Fe–Ti oxides

Opaque minerals in the shoshonite and latite lavas have highcontents of TiO2 (6.4–11.0 wt%) and Fe2OT

3 (78.2–83.8 wt%), indicat-ing that the analyzed minerals are titanomagnetite. This mineralalso occurs in the andesite, although at very low concentrations(<3%).

4. Geochemistry

4.1. Major elements

To determine the chemical characteristics of the volcanic rocksin the study area, 15 samples from the Post-Eocene succession and25 samples from the Eocene succession were analyzed by induc-tively coupled plasma–mass spectrometry (ICP–MS) (Tables 4and 5). Samples were crushed and pulverized in an agate mill,and analyzed by ICP–MS at Actlabs (Canada) using the lithiummetaborate/tetraborate fusion ICP Whole Rock Package. A portionof sample pulp was mixed with flux (lithium metaborate, LiBO2)to lower the melting point. The mixture was then heated in a muf-fle furnace until molten. After cooling, the fused mass was digestedin 5% HNO3 and the resulting clear solution was analyzed.

The analyses reveal that rocks in the study area belong to threegroups, based on the classification scheme proposed by Le Maitreet al. (2002): (1) shoshonite (SiO2 = 48–51 wt%), (2) latite andandesite (SiO2 = 57–59 wt%), and (3) rhyolite (SiO2 = 68–73 wt%)(Fig. 8 and Table 4). Some of the LOI values are somewhat high(e.g., S4R19, 3.7 wt%; S5BR10, 5.3 wt%), indicating subaqueousweathering. Although modal quartz is observed only in the andes-ite and rhyolite, the shoshonite and latite contain roughly 3 wt%and 10 wt% normative quartz, respectively. The contents of norma-tive hypersthene show a decrease from mafic to felsic rock types(approximately 5 wt% in shoshonite, 4 wt% in latite, and 1 wt% inrhyolite), with the highest contents in andesite (>6%).

Most of the rocks have Na2O � 2.0 < K2O; such high-K values aretypical of calc-alkaline affinities. According to the modified alkali-lime index (MALI) proposed by Frost et al. (2001), representativepoints of the series plot between the calc-alkaline and alkali-calcicfields. Note that the andesites differ from the three other lavas inthat they are relatively poor in alkalis.

The samples of Eocene volcanics occupy the same fields as thePost-Eocene succession (Fig. 8), between shoshonite and dacite,and also have Na2O � 2 < K2O. Therefore, the Eocene volcanics gen-erally belong to the high-K calcalkaline to shoshonitic series(Fig. 8b).

Fig. 9 shows variations in major and two minor elements vs.SiO2. In some of the Harker diagrams (e.g., Al2O3, P2O5, K2O, and

Table 2Chemical composition of selected pyroxene grains from samples of shoshonite (S5BR7, S4R4, R37), latite (S6R8, R36), and andesite (S8BR1). The grains are clinopyroxene exceptfor analyses 107, 51, and 52, which are orthopyroxene. Compositions were calculated based on four cations. Wollastonite, enstatite, and ferrosilite contents are presented inmole%. Components are presented in mole%, following the sequence of Lindsley (1983).

Sample S5BR7 S4R4 R37 S6R8 R36 S8BR1

Analysis 15 16 125 109 124 107 133 150 160 110 27(c) 28(r) 51(c) 52(r)

SiO2 49.50 48.33 49.79 52.29 52.49 52.65 49.16 50.74 50.45 52.40 51.88 52.31 53.90 54.37TiO2 0.81 1.00 0.78 0.40 0.35 0.27 0.56 0.51 0.48 0.39 0.63 0.46 0.36 0.37Al2O3 5.85 6.10 5.28 2.06 2.35 1.04 5.20 3.12 3.13 2.59 2.38 2.26 1.30 1.10Cr2O3 0.01 0.01 0.07 0.10 0.02 0.00 0.06 0.02 0.02 0.02 0.00 0.00 0.00 0.00FeO 7.56 8.82 7.39 7.96 8.02 20.25 9.20 8.67 8.22 8.53 8.84 9.02 17.47 17.01MnO 0.17 0.22 0.14 0.35 0.40 1.06 0.28 0.52 0.51 0.56 0.40 0.32 0.47 0.56MgO 13.93 13.48 14.06 15.70 15.77 21.34 13.91 14.95 15.09 15.79 14.90 14.90 24.81 24.97CaO 23.33 22.43 21.53 20.74 20.57 1.77 20.32 20.46 20.84 19.85 21.17 21.22 1.72 1.66Na2O 0.28 0.29 0.33 0.24 0.29 0.14 0.43 0.38 0.34 0.41 0.31 0.33 0.01 0.02Total 101.44 100.68 99.37 99.84 100.26 98.52 99.12 99.37 99.08 100.54 100.51 100.82 100.04 100.06

Si 1.804 1.781 1.849 1.933 1.930 1.983 1.837 1.888 1.880 1.923 1.914 1.924 1.966 1.976Ti 0.022 0.028 0.022 0.011 0.010 0.008 0.016 0.014 0.013 0.011 0.017 0.013 0.010 0.010Al 0.251 0.265 0.231 0.090 0.102 0.046 0.229 0.137 0.137 0.112 0.103 0.098 0.056 0.047Cr 0.000 0.000 0.002 0.003 0.001 0.000 0.002 0.001 0.001 0.001 0.000 0.000 0.000 0.000Fe+2 0.114 0.135 0.183 0.209 0.204 0.638 0.096 0.088 0.102 0.211 0.213 0.227 0.533 0.517Fe+3 0.117 0.137 0.047 0.037 0.043 0.000 0.192 0.182 0.154 0.051 0.059 0.051 0.000 0.000Mn 0.005 0.007 0.004 0.011 0.012 0.034 0.009 0.016 0.016 0.017 0.012 0.010 0.015 0.017Mg 0.757 0.740 0.779 0.865 0.865 1.198 0.775 0.829 0.838 0.864 0.819 0.817 1.349 1.353Ca 0.911 0.886 0.857 0.822 0.810 0.071 0.813 0.816 0.832 0.780 0.837 0.836 0.067 0.065Na 0.020 0.021 0.024 0.017 0.021 0.010 0.031 0.027 0.025 0.029 0.022 0.024 0.001 0.001Total 4.001 4.001 4.001 3.999 4.001 3.995 4.001 4.000 3.999 4.000 3.998 4.002 3.997 3.991

AlIV 0.196 0.219 0.151 0.067 0.070 0.017 0.163 0.112 0.120 0.077 0.086 0.076 0.034 0.024AlVI 0.055 0.046 0.081 0.023 0.032 0.029 0.066 0.025 0.017 0.035 0.017 0.022 0.022 0.023%Wo 51.12 50.31 47.11 43.35 43.11 3.72 45.67 44.66 45.61 42.05 44.78 44.47 3.44 3.36%En 42.48 42.02 42.83 45.62 46.04 62.82 43.54 45.38 45.94 46.58 43.82 43.46 69.21 69.92%Fs 6.40 7.67 10.06 11.02 10.86 33.46 10.79 9.96 8.44 11.37 11.40 12.07 27.35 26.72ac NaFeSi2O6 0.02 0.02 0.02 0.02 0.02 0.00 0.03 0.03 0.02 0.03 0.02 0.02 0.00 0.00jad NaAlSi2O6 0.00 0.00 0.00 0.00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00Na(Fe2,Ti)Si2O6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00CaFeFeSiO6 0.10 0.12 0.02 0.02 0.01 0.00 0.06 0.06 0.07 0.02 0.03 0.03 0.00 0.00CaCrAlSiO6 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00CaTiAlAlO6 0.02 0.03 0.08 0.02 0.03 0.03 0.06 0.03 0.02 0.01 0.02 0.01 0.02 0.03CaAlAlSiO6 0.15 0.16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.05 0.05 0.05 0.00 0.00Wo Ca2Si2O6 0.32 0.29 0.38 0.39 0.38 0.02 0.34 0.37 0.37 0.35 0.37 0.37 0.02 0.02En Mg2Si2O6 0.38 0.37 0.39 0.43 0.43 0.60 0.39 0.41 0.42 0.43 0.41 0.41 0.68 0.68Fe Fe2Si2O6 0.01 0.01 0.08 0.10 0.11 0.34 0.07 0.07 0.05 0.11 0.10 0.10 0.27 0.27Total 1.00 1.00 0.98 0.99 0.99 1.00 0.96 0.96 0.96 1.00 1.00 1.00 1.00 1.00


Sr), representative points of the andesitic samples plot away fromthe representative points of shoshonites, latites, and rhyolites. Anevolutionary trend (arrows) is evident from shoshonite to latiteand rhyolite, suggesting a genetic relationship. The trend is definedby decreasing concentrations of MgO, CaO, TiO2, FeOt, and P2O5

with increasing SiO2. Concentrations of Al2O3, Na2O, La, and Srshow an increase from shoshonite to latite, and a subsequent de-crease to rhyolite. K2O contents show a strong continuous increasetoward rhyolite. These findings are consistent with multi-elementand rare earth element (REE) patterns and ratio–ratio plots (Figs.10 and 11, see below).

4.2. Multi-element and REE patterns

The analyzed samples yield similar multi-element patterns nor-malized to mid-ocean ridge basalt (MORB) (Pearce, 1983) and REEpatterns normalized to chondrite (Nakamura, 1974) (Fig. 10). Anorigin in a subduction-related regime (Marchev et al., 2004; Nich-olson et al., 2004) is indicated by enrichment in REEs (10–100times chondrite), enrichment in light REEs (LREEs) relative to hea-vy REEs (HREEs), enrichment in large-ion lithophile elements(LILEs), and depletion of some high field strength elements (HFSEs)such as Nb and Ta.

A number of geochemical differences were also found amongthe samples. First, the shoshonite and latite have the typicalgeochemical signatures of magmas that formed in a subduction-

related regime, including strong negative anomalies in HFSEs (Ta,Nb, Zr, and Hf) and strong enrichment in LREEs. Second, the rhyo-lite shows a REE pattern (Fig. 10d) similar to that of cold-wet-oxi-dized rhyolites reported by Christiansen (2005) and Christiansenand McCurry (2008), interpreted to indicate a subduction zone set-ting. Moreover, the rhyolite and andesite show negative anomaliesin Ba, P, and Eu. Avanzinelli et al. (2008) examined potassium-richvolcanic rocks in Italy, and proposed that the depletion of Ba in vol-canic rocks may be independent of the degree of silica saturation,instead reflecting the composition of the sedimentary rocks fromwhich the magmatic rocks were derived. Third, the same patternsare seen in the Eocene volcanics (see the gray field in Fig. 10), bothin the shoshonites and in the rhyolites.

The REE and MORB patterns obtained for the shoshonite and la-tite are similar to each other but differ somewhat from those of theandesite and rhyolite, including differences in the HFSE and Euanomalies (Fig. 10). In contrast, the REE characteristics of andesiteare similar to those of rhyolite (e.g., both contain negative anoma-lies in Ba, Eu, and P).

4.3. Tectonic setting

The analyzed volcanic rocks, when plotted in various tectonicdiscrimination diagrams, fall in the subduction-related volcanicarc field. The various plots show that the samples belong to thehigh-K calcalkaline series (Figs. 8b and 11a), except for shoshonites

Fig. 6. (a) Chemical compositions of pyroxene phenocrysts plotted in an En–Wo–Fs ternary diagram. Left to right: shoshonite, latite, and andesite. (b) Na + AlIV vs.AlIV + 2Ti + Cr plot (Schweitzer et al., 1979), revealing a strong linear trend for pyroxene phenocrysts and indicating high oxygen fugacity. (c) Composition of pyroxenes in aplot of Ti + Cr vs. Ca (Leterrier et al., 1982), indicating their formation in an orogenic arc.


that typically belong to the shoshonitic series. The samples are‘‘orogenic andesite’’ (Fig. 11c) that evolved at an active continentalmargin (Fig. 11b and d). The magmas appear to have evolved in avolcanic back-arc setting, as indicated in the K2O/SiO2 diagram(Peccerillo and Taylor, 1976), in which the rocks belong to thehigh-K series.

In the geological framework of Iran, the evolution of such high-K calcalkaline magmas have been related to the subduction of Neo-tethyan oceanic lithosphere beneath Central Iran microplates dur-ing the lower Triassic to upper Cretaceous, followed by continentalcollision of the Arabian Plate with Iranian microplates from the Eo-cene to the present (e.g., Alavi, 1994; Berberian and Berberian,1981; Golonka, 2004). The NW–SE-trending Urumieh Dokhtarmagmatic assemblage, which is oriented parallel to the ZagrosThrust, as well as the E–W-trending Alborz magmatic assemblagelocated behind the Urumieh Dokhtar magmatic assemblage, areinterpreted as a continental margin volcanic arc and an abortedback-arc basin, respectively.

5. Petrogenetic processes

5.1. Eruption style

Volcanic activity in the Abazar area shows evidence of varia-tions in eruption styles (indicating both explosive and effusiveeruptions) and in chemical compositions (Table 5). Based on fieldstudies, petrographic data, and geochemical characteristics, thevolcanic deposits could be grouped into two main events: (1)pyroclastic flow deposits (a rhyolitic ignimbritic sheet) that weresubaerially emplaced by a vapor-rich eruption column, and (2)overlying mafic–intermediate lava flows with a compositiondistinct from that of the pyroclastic rocks. These latter lava flowsindicate an effusive eruption that essentially produced low-viscos-ity lava with occasional relatively viscous liquid, as indicated bythe relatively small number of scoriaceous units intercalated

within the flows. Various petrogenetic processes occurred in mag-ma chambers emplaced within continental crust.

5.2. Fractional crystallization

Geochemical data clearly indicate a genetic relation betweenthe shoshonites, latites, and rhyolites (Harker diagrams and REEmulti-element patterns; see Section 4; Fig. 9), which form a volca-nic series. Fractional crystallization is invoked to explain the gene-sis of latitic and rhyolitic melts from shoshonitic melt. The mainmineral phases that crystallized, resulting in decreasing MgO,CaO, Al2O3, FeOt, and TiO2 contents, and increasing alkali (Na2O + -K2O) contents vs. SiO2, are as follows:

– Differentiation of olivine + Ca-rich pyroxene + Ca-rich plagio-clase + Ti-magnetite from shoshonitic lavas at shallow depth(�10 km) to produce latitic lavas.

– Separation of augite + diopside + Ca–Na plagioclase ± Mg-hastingsite from latitic lavas to produce rhyolitic melts at shal-low depth (�5 km).

However, the presence of abundant Mg-hastingsite and biotitein rhyolitic ignimbrite and the absence of any characteristic trendin K2O variations indicate that the most differentiated melts werelikely contaminated by crustal melts. This proposal is supported bythe fact that the andesitic samples depart from the evolutionarytrends defined by the other samples.

5.3. Magma mixing and/or mingling

Numerous studies of magma genesis and fluid behavior haveshown that the chemistry and eruptive styles of some magmasare controlled by the mixing and/or mingling of separately formedor separately evolved magma batches (e.g., Bardintzeff, 1992;Eichelberger et al., 2000; Huppert et al., 1982; O’Hara andMatthews, 1981; Sparks et al., 1977; Woods and Cowan, 2009),

Tabl

e3

Chem

ical

com

posi

tion

ofse

lect

edam

phib

ole

grai

nsfr

omsa

mpl

esof

lati

te.C

ompo

siti

ons

wer

eca

lcul

ated

base

don

22ox

ygen

s.

Sam

ple

S6R

4R

36S6

R5

An

alys

is53

5461

6263

6467

6878

84(c

)97

(c)

98(m

)99

(r)

100

101

132(

c)13

3(r)

134

SiO

243

.04

42.8

441

.60

42.5

242

.22

43.4

343

.11

42.8

542

.65

41.8

944

.06

42.2

042

.30

40.7

542

.28

43.2

942

.49

43.0

8Ti

O2

2.72

2.76

2.39

2.46

2.45

2.42

2.35

2.48

2.73

2.53

2.40

2.31

2.61

2.11

2.59

2.38

2.42

2.63

Al 2

O3

12.1

412

.11

12.7

012

.22

12.7

712

.25

12.1

712

.17

12.3

011

.60

10.4

812

.35

11.8

713

.71

12.2

411

.64

11.9

712

.07

FeO

12.3

012

.26

12.2

012

.11

12.7

611

.47

12.5

412

.06

12.1

212

.79

10.5

412

.08

11.9

912

.29

12.3

311

.84

12.1

711

.68

Mn

O0.

330.

260.

240.

210.

230.

270.

220.

310.

290.

420.

330.

270.

240.

200.

350.

430.

270.

28M

gO13

.56

13.6

512

.96

13.8

912

.74

13.7

713

.87

13.7

813

.67

13.9

014

.55

14.0

014

.00

13.5

414

.02

13.2

413

.89

13.9

4C

aO11

.90

11.8

212

.18

11.7

812

.27

11.8

311

.65

11.6

511

.78

10.7

511

.96

11.1

611

.01

11.3

411

.11

10.7

011

.01

11.0

6N

a 2O

2.33

2.19

2.37

2.28

2.24

2.34

2.29

2.21

2.30

2.43

2.55

2.39

2.41

2.48

2.34

2.57

2.17

2.28

K2O

0.79

0.88

0.93

0.89

0.89

0.83

0.75

0.83

0.93

0.81

0.73

0.85

0.79

0.71

0.93

0.82

0.84

0.85

Cl

0.03

0.01

0.02

0.01

0.05

0.02

0.03

0.04

0.04

0.03

0.02

0.04

0.02

0.00

0.04

0.01

0.00

0.05

Tota

l99

.14

98.7

897

.59

98.3

798

.62

98.6

398

.98

98.3

898

.81

97.1

597

.62

97.6

597

.24

97.1

398

.23

96.9

297

.23

97.9

2

Si6.

198

6.18

46.

121

6.15

76.

147

6.26

96.

194

6.19

56.

159

6.12

56.

420

6.13

46.

176

5.95

76.

110

6.34

56.

194

6.23

8Ti

0.29

50.

300

0.26

40.

268

0.26

80.

263

0.25

40.

270

0.29

60.

278

0.26

30.

252

0.28

70.

232

0.28

10.

262

0.26

50.

286

Al

2.06

02.

060

2.20

22.

085

2.19

12.

084

2.06

12.

074

2.09

31.

999

1.80

02.

116

2.04

32.

362

2.08

52.

011

2.05

62.

060

Fe+

21.

005

0.98

01.

105

0.90

31.

143

1.01

40.

900

0.88

00.

954

0.72

81.

006

0.75

90.

848

0.73

70.

746

0.99

80.

797

0.86

0Fe

+3

0.47

60.

500

0.39

60.

563

0.41

10.

371

0.60

70.

578

0.50

90.

836

0.27

80.

709

0.61

60.

765

0.74

40.

454

0.68

70.

554

Mn

0.04

00.

032

0.03

00.

026

0.02

80.

033

0.02

70.

038

0.03

50.

052

0.04

10.

033

0.03

00.

025

0.04

30.

053

0.03

30.

034

Mg

2.91

12.

938

2.84

32.

998

2.76

52.

963

2.97

12.

970

2.94

33.

030

3.16

03.

034

3.04

72.

951

3.02

12.

893

3.01

83.

009

Ca

1.83

61.

828

1.92

01.

828

1.91

41.

830

1.79

41.

805

1.82

31.

684

1.86

71.

738

1.72

21.

776

1.72

01.

680

1.72

01.

716

Na

0.65

10.

613

0.67

60.

640

0.63

20.

655

0.63

80.

620

0.64

40.

689

0.72

00.

674

0.68

20.

703

0.65

60.

730

0.61

30.

640

K0.

145

0.16

20.

175

0.16

40.

165

0.15

30.

137

0.15

30.

171

0.15

10.

136

0.15

80.

147

0.13

20.

171

0.15

30.

156

0.15

7Su

m15

.636

15.6

1415

.741

15.6

4615

.682

15.6

4515

.600

15.5

9815

.649

15.5

9315

.702

15.6

2415

.614

15.6

5015

.605

15.5

9215

.550

15.5

71

c=

core

;m

=m

iddl

e;r

=ri

m.

Fig. 7. Chemical compositions of amphiboles within latite, as plotted on a Mg# vs.Si diagram (Leake et al., 1997).


and controlled by the nature and extent of pre-eruptive degassing(e.g., Barclay et al., 1996; Eichelberger et al., 1986; Fink and Manley,1987; Mastrolorenzo et al., 1993; Piochi et al., 2005). If volatilesbecome saturated, gas bubbles are exsolved and may rise upwards(Bond and Sparks, 1976; Cordoso and Woods, 1999; Synder andTait, 1995; Thomas et al., 1993).

According to Phillips and Woods (2002) and Woods and Cowan(2009), a temperature contrast is established in a magma chamberwhen a pulse of new mafic magma is intruded into the base of thechamber. Because of the temperature contrast between the newand existing magma, the lower, hot, mafic melt is cooled and even-tually may crystallize, leading to an increase in the volatile contentof the residual melt. At some point, the volatiles may become sat-urated and gas bubbles are exsolved, leading to a reduction in thebulk density of the mixture of mafic magma, crystals, and bubbles.As crystallization proceeds, the bulk density of the lower layer de-creases via the continuing growth of crystals and bubbles, as wellas by crystal settling or bubble ascent and separation. If theproduction rate of crystals and bubbles exceeds the rate of theirseparation from the bulk mixture, the bulk density may eventuallydecrease below that of the upper layer, leading to mixing of thetwo layers via plumes of the lower layer rising through the upperlayer (Huppert et al., 1982).

In the present study, multi-element patterns and HFSE plots re-veal that the andesitic lava was not generated from the shosho-nite–latite trend. Mingling between the andesitic magma andlatitic magma is indicated by the occurrence of enclaves of the for-mer in the later (Fig. 3d). In addition, the volatile-saturation of themagma is indicated by the occurrence of Mg-hastingsite pheno-crysts in both the latite and andesite. According to Foden andGreen (1992), the crystallization of amphibole in andesitic magmasmay occur if cooling of the liquid and mineral growth occur duringequilibrium crystallization within a closed system. This mode ofcrystallization occurs when the magma body becomes stationaryin the crust, although subjected to turbulent flow within the cham-ber. Under these conditions, vigorous convection and mixing occurin the interior of the magma body, with the result that phenocrystsand melt remain in equilibrium. Based on model suggested byIzbekov et al. (2004), numerous replenishment events may acceler-ate the convective forces and enhance mingling of the two mag-mas, possibly resulting in homogenization of the hybrid magmain the chamber.

The equilibrium temperatures of the latititic and andesitic mag-mas are similar to each other, as indicated by the similar plagio-clase compositions in both rocks (Fig. 5b). The initial magmatemperatures were probably also similar, and any difference would

Table 4Major element (wt%) and trace element (ppm) data for volcanic rocks from the Abazar area, North Qazvin, Iran.

Sample no. S4R19 S4R4 S5BR10 S5BR7 R36 R44 S6R4 S6R5 S6R7 S7BR1 S8BR1 S11TR2 S11TR1 S2TR2 S2TR4

Shoshonites Latites Andesites Rhyolites

SiO2 49.30 51.40 47.80 51.10 57.20 57.40 57.30 56.90 58.20 59.30 59.10 68.20 73.40 69.70 68.20Al2O3 18.10 17.55 17.10 17.50 18.00 18.05 18.00 17.80 18.10 15.85 15.95 14.55 12.70 12.95 15.10Fe2O3 10.20 8.97 9.59 9.58 6.29 6.59 6.27 6.22 6.38 6.14 6.16 3.12 2.62 2.64 3.22MgO 3.22 3.83 2.75 4.30 2.08 1.76 1.86 1.96 2.00 2.90 2.92 0.60 0.52 0.53 0.62CaO 7.53 8.81 9.52 9.51 5.67 5.79 5.49 5.70 5.66 5.38 5.40 1.96 1.60 2.71 2.07Na2O 2.90 3.13 2.66 2.98 4.02 4.06 4.06 4.02 4.10 3.98 3.59 3.78 2.99 3.15 3.98K2O 3.02 2.54 3.00 1.81 2.76 2.76 2.83 2.82 2.88 1.90 2.34 4.31 4.62 4.61 4.53Cr2O3 <0.01 0.01 <0.01 0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01TiO2 1.08 0.96 1.02 1.03 0.63 0.64 0.61 0.61 0.61 0.74 0.75 0.40 0.34 0.33 0.42MnO 0.16 0.13 0.14 0.16 0.09 0.10 0.11 0.11 0.11 0.11 0.12 0.10 0.09 0.09 0.10P2O5 0.39 0.38 0.37 0.32 0.36 0.35 0.34 0.34 0.34 0.22 0.21 0.14 0.13 0.12 0.14SrO 0.07 0.08 0.06 0.07 0.07 0.07 0.07 0.07 0.07 0.05 0.05 0.02 0.02 0.02 0.03BaO 0.08 0.08 0.11 0.07 0.10 0.10 0.10 0.13 0.23 0.07 0.08 0.08 0.07 0.07 0.08LOI 3.68 1.78 5.30 1.27 1.75 2.27 2.06 2.27 1.39 2.17 2.10 0.79 0.67 2.39 1.38Total 99.73 99.65 99.42 99.71 99.02 99.94 99.10 98.95 100.07 98.81 98.77 98.05 99.77 99.31 99.87

Ag <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1 <1Ba 723 683 879 606 841 812 844 1085 1920 632 641 685 574 596 689Ce 44.4 52.4 41.4 34.9 53.9 55.8 58.2 57.7 58.1 53.0 57.0 59.2 51.1 52.6 60.0Co 27.7 26.7 25.4 27.4 12.7 12.3 12.7 13.2 12.7 16.6 16.8 4.4 3.4 3.5 4.4Cr 10 40 10 50 10 20 10 10 10 30 30 <10 <10 <10 <10Cs 3.47 1.13 1.63 1.38 1.42 1.68 1.62 1.56 1.55 2.85 3.84 1.13 0.86 0.79 1.14Cu 81 50 91 78 19 25 19 18 15 45 46 9 8 8 9Dy 4.92 4.80 4.50 4.23 4.08 4.25 4.01 4.10 4.16 4.17 4.25 4.27 3.53 3.61 4.27Er 2.78 2.65 2.53 2.45 2.47 2.64 2.56 2.60 2.53 2.51 2.56 2.80 2.31 2.38 2.83Eu 1.87 1.76 1.69 1.49 1.60 1.56 1.56 1.55 1.59 1.19 1.14 1.09 0.91 0.91 1.15Ga 19.1 18.3 17.4 17.6 18.2 18.3 18.3 18.2 18.7 16.6 16.8 14.9 12.5 12.8 15.2Gd 5.87 6.03 5.57 4.78 5.17 5.18 5.12 5.19 5.23 4.89 4.74 4.86 3.99 4.14 4.87Hf 2.8 3.5 2.4 2.5 4.2 4.2 4.1 4.1 4.1 5.1 5.5 6.2 5.1 5.4 6.1Ho 0.99 0.94 0.89 0.88 0.84 0.87 0.85 0.84 0.85 0.86 0.88 0.89 0.74 0.76 0.90La 22.3 25.8 19.9 17.1 28.1 28.2 29.7 29.5 29.6 26.6 28.9 31.0 26.5 27.0 31.3Lu 0.37 0.36 0.34 0.35 0.39 0.41 0.38 0.41 0.41 0.39 0.38 0.47 0.40 0.40 0.46Mo 3 2 2 <2 <2 2 2 2 2 3 3 2 2 2 2Nb 7.1 9.9 6.6 7.1 11.9 11.9 12.1 11.9 12.2 13.2 13.1 16.4 14.0 14.6 16.7Nd 25.4 27.6 23.3 19.3 25.9 26.6 27.0 26.7 26.8 24.0 25.4 24.5 20.9 21.2 24.9Ni 14 16 12 16 8 9 7 8 8 13 13 <5 <5 <5 <5Pb 17 14 12 13 15 14 16 15 17 17 42 17 14 15 15Pr 5.97 6.75 5.46 4.61 6.76 6.83 7.07 6.93 7.00 6.29 6.60 6.82 5.79 5.92 6.84Rb 77.0 66.5 75.6 46.0 72.9 73.1 77.2 76.5 78.7 111.5 169.0 130.5 127.5 126.5 131.0Sm 5.85 5.98 5.41 4.51 5.03 5.19 5.28 5.23 5.08 4.78 4.88 4.70 3.95 3.95 4.65Sn 1 1 1 1 1 1 1 1 1 2 2 1 1 1 1Sr 596 634 519 549 577 591 580 590 613 388 403 239 181 190 244Ta 0.4 0.6 0.4 0.4 0.7 0.7 0.7 0.7 0.7 0.9 1.0 1.2 1.0 1.1 1.2Tb 0.91 0.86 0.82 0.76 0.74 0.75 0.74 0.74 0.74 0.72 0.85 0.74 0.59 0.62 0.73Th 4.93 6.38 4.40 4.05 7.50 7.51 7.47 7.27 7.38 11.40 11.70 15.75 13.70 14.05 15.65Tl <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 <0.5 1.5 <0.5 <0.5 <0.5 <0.5Tm 0.38 0.37 0.34 0.35 0.36 0.37 0.36 0.38 0.37 0.36 0.39 0.44 0.36 0.36 0.43U 1.54 1.69 1.33 1.07 2.05 2.03 1.98 1.91 1.99 3.30 3.50 3.32 3.03 3.19 3.31V 252 207 227 237 104 109 100 100 100 136 140 60 47 48 60W 2 2 2 1 2 2 2 2 2 3 3 4 3 3 2Y 24.0 24.1 22.5 21.4 21.2 22.2 22.1 22.2 22.4 22.3 23.6 23.0 19.4 20.1 23.2Yb 2.40 2.39 2.21 2.23 2.49 2.64 2.47 2.49 2.54 2.51 2.54 2.87 2.49 2.50 2.97Zn 119 92 90 86 88 89 91 86 89 67 62 57 45 46 55Zr 101 134 93 96 167 168 172 168 171 198 204 233 192 203 234Qz 2.63 3.17 1.48 4.42 9.64 9.95 9.81 9.38 9.91 14.83 14.99 25.02 34.49 28.57 22.75Co 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.44 0.18 0.00 0.22Or 17.85 15.01 17.73 10.70 16.31 16.31 16.72 16.67 17.02 11.23 13.83 25.47 27.30 27.24 26.77Ab 24.54 26.49 22.51 25.22 34.02 34.35 34.35 34.02 34.69 33.68 30.38 31.99 25.30 26.65 33.68An 27.45 26.33 25.86 29.03 22.92 22.87 22.53 22.19 22.48 19.77 20.49 8.81 7.09 7.58 9.35Di 3.29 9.38 12.42 10.20 0.79 1.34 0.62 1.69 1.31 2.60 2.17 0.00 0.00 2.85 0.00Wo 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.26 0.00Hy 6.50 5.19 1.09 5.98 4.81 3.76 4.35 4.10 4.37 6.02 6.27 1.49 1.30 0.00 1.54Il 0.34 0.28 0.30 0.34 0.19 0.21 0.24 0.24 0.24 0.24 0.26 0.21 0.19 0.19 0.21Hm 10.20 8.97 9.59 9.58 6.29 6.59 6.27 6.22 6.38 6.14 6.16 3.12 2.62 2.64 3.22Tn 2.21 2.00 2.12 2.09 1.30 1.29 1.19 1.19 1.19 1.51 1.51 0.00 0.00 0.56 0.00Ru 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.29 0.24 0.00 0.31Ap 0.92 0.90 0.88 0.76 0.85 0.83 0.81 0.81 0.81 0.52 0.50 0.33 0.31 0.28 0.33


have been reduced during mingling of the two magmas. The tem-peratures of mixed/mingled magmas generally vary by 50–200 �C(see the review by Bardintzeff, 1992). In the present case, the low-est value of 50 �C seems reasonable.

The andesitic magma, which is slightly richer in SiO2 than thelatitic magma (59 wt% against 57 wt%, respectively) and wasslightly cooler, would have been relatively viscous, thereby pre-venting complete magma mixing. Moreover, the crystal content,

Table 5Major element (wt%) and trace element (ppm) data of Eocene volcanic rocks of North Qazvin, Iran.

Sample no. SK39 SK40 SK42 SK74 Z.05.1 Z.05.3 ZS.01.2 ZB.01 ZN.10.1 ZNS.01 ZD.01 ZD.28

Shoshonite

SiO2 55.73 54.43 54.15 53.57 56.33 56.09 52.77 49.13 52.52 54.12 52.80 47.49Al2O3 18.59 18.60 16.21 19.71 20.42 20.46 17.54 16.76 17.35 18.34 17.56 17.37Fe2O3 7.39 7.36 9.09 7.99 6.73 6.93 8.79 10.13 9.18 8.21 8.25 10.33MgO 2.55 2.47 4.28 1.15 1.92 1.57 5.02 7.48 4.99 3.17 4.29 6.09CaO 8.05 7.57 8.36 7.73 6.92 7.20 7.27 10.92 8.30 7.61 11.23 12.38Na2O 3.24 3.21 2.81 3.44 3.41 3.45 4.02 2.22 2.94 3.29 2.85 2.63K2O 2.73 2.79 2.27 3.29 2.64 2.66 3.03 1.97 3.13 3.62 1.62 2.14TiO2 0.98 0.95 0.96 1.04 1.05 1.06 1.06 0.95 1.09 1.11 0.97 1.15MnO 0.13 0.09 0.20 0.07 0.07 0.08 0.14 0.16 0.14 0.12 0.19 0.18P2O5 0.23 0.27 0.23 0.31 0.55 0.55 0.42 0.32 0.43 0.47 0.28 0.32

Total 99.62 97.74 98.56 98.30 100.04 100.04 100.05 100.04 100.07 100.06 100.04 100.08V 205 195 255 225 118 116 216 247 233 199 210 261Cr 40 40 50 30 <20 <20 70 80 80 20 160 50Co 20 17.5 26 17 8 8 20 30 22 16 24 23Ni 15 15 20 15 <20 <20 30 50 40 20 60 30Zn 85 85 95 95 60 60 60 70 70 70 70 80Ga 20 20 19 21 14 15 13 12 14 14 14 13Rb 70.6 73.2 56.2 106 57 57 75 43 73 90 32 38Sr 553 550 470 574 509 519 791 460 526 545 492 550Y 27 27 28 31.5 29.7 28.8 22.7 19.7 24.9 24.4 22.6 20.9Zr 158 155.5 132 219 201 199 142 89 156 179 110 88Nb 13 13 10 20 12.8 12.9 12.1 6.7 13.5 14.6 8.8 7.3Sn 1 2 2 3 2 2 2 1 2 2 2 3Cs 1 0.9 1.1 1.5 0.9 0.9 2 1.1 1.4 1.1 0.7 0.9Ba 611 595 500 715 661 680 591 451 598 657 572 608La 30 29 26 38 30.9 30.3 27.7 18 30 32.8 24.6 20.1Ce 56.5 54.5 48 73 60.9 60.1 55.1 36.8 60.6 64.3 49.9 42.5Pr 6.8 6.7 6.1 8.8 7.5 7.4 6.5 4.5 7.1 7.5 5.9 5.3Nd 26.5 26.5 24.0 34.5 29.8 28.6 26.2 18.9 27.7 29.5 24.0 22.2Sm 5.7 5.5 5.3 6.7 6.4 6.3 5.6 4.4 6.0 6.2 5.2 5.1Eu 1.5 1.5 1.5 1.7 1.8 1.8 1.7 1.4 1.7 1.7 1.5 1.5Gd 5.6 5.5 5.5 6.7 6.3 6.2 5.3 4.5 5.7 5.8 5.0 4.8Tb 0.8 0.8 0.8 1.0 1.1 1.0 0.8 0.7 0.9 0.9 0.8 0.8Dy 4.7 4.6 5.1 5.7 5.6 5.6 4.6 4.0 4.9 4.9 4.4 4.3Ho 0.9 1.0 1.0 1.1 1.1 1.1 0.9 0.8 0.9 0.9 0.9 0.8Er 2.9 2.9 3.1 3.4 3.3 3.2 2.5 2.2 2.7 2.7 2.5 2.3Tm 0.4 0.4 0.5 0.5 0.5 0.5 0.4 0.3 0.4 0.4 0.4 0.3Yb 2.7 2.7 2.7 3.1 3.1 3.0 2.3 1.9 2.6 2.6 2.3 2.1Lu 0.4 0.4 0.4 0.5 0.5 0.5 0.3 0.3 0.4 0.4 0.3 0.3Hf 5.0 5.0 4.0 6.0 5.1 5.2 3.6 2.2 4.0 4.4 3.2 2.7Ta 0.5 0.5 0.5 1.0 0.9 0.9 0.8 0.4 0.9 1.0 0.6 0.4W 4.0 3.0 3.0 5.0 1.8 1.4 1.6 0.7 1.1 1.8 1.0 1.0Th 7.0 7.0 6.0 15.0 7.2 7.3 5.6 2.4 6.4 7.6 5.9 4.0U 2.0 1.5 1.5 3.5 1.8 1.9 1.7 0.7 1.9 2.3 1.5 1.1

SK29 SK31 SK37 SK75 SS20 ZS.06 ZS.07 ZDS.01 ZSD.01 SM16 SM24 SM45 SM50

Latite Dacite

SiO2 58.17 59.33 58.77 59.39 59.57 68.63 68.65 63.71 63.30 64.61 67.58 67.18 64.63Al2O3 15.35 15.64 15.60 16.40 15.49 17.27 17.30 17.80 17.76 15.20 14.63 16.69 15.22Fe2O3 8.44 8.24 7.78 6.37 8.27 2.36 2.39 4.68 5.07 4.19 3.58 3.08 3.93MgO 1.99 1.92 1.81 2.51 2.03 0.85 0.87 1.83 2.09 2.13 1.05 0.95 1.33CaO 4.57 4.94 5.39 4.81 5.93 2.62 2.59 3.63 3.43 1.90 1.52 0.73 2.24Na2O 3.10 3.16 3.24 3.22 3.21 4.30 4.27 4.21 4.53 4.58 5.43 8.29 5.03K2O 4.50 4.60 4.13 4.39 4.38 3.48 3.45 3.20 2.86 2.93 2.48 0.82 2.61TiO2 1.28 1.27 1.22 0.72 1.27 0.26 0.26 0.56 0.60 0.79 0.55 0.62 0.78MnO 0.11 0.12 0.15 0.05 0.12 0.08 0.07 0.09 0.08 0.10 0.10 0.08 0.06P2O5 0.46 0.40 0.41 0.15 0.40 0.17 0.17 0.29 0.30 0.21 0.10 0.13 0.14

Total 97.97 99.62 98.50 98.01 100.67 100.01 100.02 99.99 100.03 96.64 97.02 98.57 95.97V 165 185 170 150 170 13 13 50 54 45 60 35 45Cr 30 30 30 50 30 <20 <20 <20 <20 10 20 10 10Co 19 17.5 18.5 19 16 2 2 5 7 5 5 2.5 3Ni 15 15 15 35 10 <20 <20 <20 <20 5 5 5 5Zn 105 110 105 80 105 60 60 50 60 95 155 80 105Ga 18 19 20 17 19 15 15 13 15 19 16 16 18Rb 126.5 134 121 135.5 124 100 102 79 77 61.6 70.6 14.8 46.5Sr 339 366 401 424 369 340 329 279 284 144.5 160.5 141.5 117Y 40.5 40.5 41 22 40 19.6 18.9 20.8 24.4 36 27 28.5 36.5Zr 256 255 254 184.5 250 216 219 167 166 178 202 202 172Nb 21 21 21 16 21 11.9 12.7 13.6 14 14 18 20 13Sn 3 3 3 2 2 3 2 2 2 2 3 2 2Cs 1.7 2.2 2.9 3.7 2.4 2.9 2.9 1 0.8 0.7 0.5 0.1 0.9

(continued on next page)


Table 5 (continued)

SK29 SK31 SK37 SK75 SS20 ZS.06 ZS.07 ZDS.01 ZSD.01 SM16 SM24 SM45 SM50

Latite Dacite

Ba 806 887 810 577 872 853 858 789 729 499 557 153 665La 45.5 45.5 45.5 29.5 44.5 34.1 34.8 36.6 33.8 32 35 19 31Ce 87.5 89 87.5 52 88 63.7 64.5 68.3 64.2 64 64 36 63Pr 10.9 10.8 10.8 6.4 10.7 6.7 6.8 7.3 7.1 8 7.3 4.4 7.9Nd 41.5 42.0 41.5 22.5 41.5 23.0 23.3 26.7 26.1 32 26 17.5 31Sm 8.6 8.4 8.5 4.6 8.4 4.2 4.2 5.2 5.1 6.8 4.8 3.8 6.5Eu 1.9 1.9 1.9 1.2 2.0 1.1 1.1 1.3 1.3 1.8 1.2 1 1.8Gd 8.7 8.4 8.8 4.7 8.6 3.5 3.5 4.4 4.6 6.8 4.9 4.3 7Tb 1.2 1.2 1.2 0.7 1.2 0.6 0.6 0.7 0.7 1.1 0.7 0.7 1.1Dy 7.2 7.2 7.2 3.7 7.2 3.2 3.3 3.9 4.1 6.4 4.4 4.7 6.4Ho 1.5 1.4 1.4 0.8 1.4 0.6 0.6 0.8 0.8 1.3 0.9 1 1.3Er 4.3 4.2 4.3 2.4 4.2 2.0 2.0 2.3 2.4 4.1 3 3.1 4.1Tm 0.6 0.6 0.6 0.4 0.6 0.3 0.3 0.4 0.4 0.6 0.5 0.5 0.6Yb 4.0 3.9 3.8 2.4 4.0 2.2 2.3 2.3 2.4 3.8 3 3.3 3.9Lu 0.6 0.6 0.6 0.4 0.6 0.3 0.3 0.3 0.4 0.6 0.5 0.5 0.6Hf 8.0 8.0 7.0 6.0 8.0 5.1 5.2 4.4 4.4 6 6 6 5Ta 1.0 1.5 1.5 1.0 1.5 1.0 1.1 1.2 1.1 0.5 1 1.5 0.5W 4.0 4.0 4.0 4.0 4.0 2.2 2.5 1.8 1.7 3 3 3 3Th 12.0 12.0 12.0 12.0 13.0 10.0 10.2 12.6 11.7 7 12 9 7U 3.0 3.0 3.0 3.5 3.0 3.1 3.2 3.5 3.8 1.5 3 2.5 2

Fig. 8. (a) Total alkali–silica diagram (Le Maitre et al., 1989) and (b) K2O/SiO2 diagram (Peccerillo and Taylor, 1976) showing data for volcanic rocks of the Abazar area, Iran.(Abbreviations: A: Andesite; B: Basalt; BA: Basaltic andesite; BTA: Basaltic trachyandesite; D: Dacite; T: Trachyte; TA: Trachyandesite; TB: Trachybasalt; TD: Trachydacite; R:Rhyolite). Analyses in (a) were recalculated to 100% based on LOI-free. These rocks are named according to their high-K content (see the main text).


along with crystal size and shape, would have dramatically in-creased the viscosity of the liquid, compared with a crystal-freemagma (McBirney and Murase, 1984). The andesite and latitewould have contained �40% and �35% crystals, respectively. How-ever, it appears that the mesostasis composition in andesitic lavawould have been more silicic than that in latitic lava.

5.4. Crustal melting

Ignimbrites are thought to originate from crustal anatexis athigh levels in continental crust (e.g., DePaolo, 1981; Gill, 1981;Patchett, 1980; Wilson, 1989). Huppert and Sparks (1988) inter-preted such felsic magma to be the product of partial melting ofcontinental crust when intruded by hot, deep-level basaltic mag-ma. In the same way, Franz et al. (1999) proposed an assimilationprocess in the genesis of benmoreitic–trachytic rocks of the Mei-dob Hills Volcanic Field in Darfur, Sudan, and Nkouathio et al.(2008) interpreted the same process for rare rocks (mugeariteand benmoreite) from Mount Bambouto, Cameroon Volcanic Line.

Rhyolites of the Abazar district have rather low Sr contents(180–240 ppm; Fig. 9) for Ba contents of 570–690 ppm, Zr contentsof 190–230 ppm, and a Zr/Nb ratio of 13.7–14.2. Their Al2O3 con-tents, which range from 15 wt% for 68 wt% SiO2 to 13 wt% for73 wt% SiO2, correspond to a small amount (<0.4 wt%) of normativecorundum. In this respect, the rhyolites differ significantly fromtypical crustal rhyolite (or granite), which is Al2O3-rich (>15 wt%Al2O3 for 70 wt% SiO2) and contains more than 3 wt% of normative

corundum. We consider that the rhyolitic ignimbrites of the Abazardistrict were produced by the differentiation of mafic magmasrather than crustal melting.

6. Concluding remarks

The Abazar volcanic district, on the southern slopes of the Al-borz Mountains, was produced by post-Eocene volcanic activityafter large-scale Eocene volcanism. The post-Eocene volcanism,which possesses the same petrological characteristics as the Eo-cene volcanics, involved subaerial explosive and then effusiveeruptions, and resulted from the sequence of events described be-low (Fig. 12).(1) Explosive gas-rich eruptions produced a thin(thickness, <10 m), extensive (�10 km2 in area), light gray rhyoliticignimbrite underlain by a lithic breccia flow (thickness, �50 m ormore). The low density of the ignimbrite and the typical occur-rence of biotite phenocrysts in a shard-rich hyaline matrix indicatean origin via a hot, gas-rich avalanche. The shards retain their ori-ginal shapes, indicating that welding did not occur.(2) Effusiveeruptions. After a period of erosion marked by a reddish soil hori-zon at the top of the ignimbritic sheet described above, lava flowsof various compositions were erupted subaerially, including shosh-onite, latite, andesite, and scarce basalt.

Chemical analyses of the volcanic rocks and their constituentcrystals reveal that the shoshonite, the latite, and the rhyoliteevolved via magmatic differentiation.

Fig. 9. Harker diagrams (wt% for major elements and ppm for La and Sr) showing data for volcanic samples from the study region. The obtained trends suggest a geneticrelation among all samples except the andesites, which plot away from the trends defined by the other samples.


Although the andesite samples show a modal mineralogicalcomposition more or less similar to those of the shoshonite and la-tite, they plot away from the trends of magma evolution defined bythe shoshonite, the latite, and the rhyolite. The element chemistryof the andesite, as shown in Harker diagrams, HFSE plots, and mul-ti-element patterns, is clearly different from that of the shoshonite,the latite, and the rhyolite, indicating the independent origin of thismagma. Subsequently, the latite and andesite mingled together.

The shoshonites and andesites yield equilibrium temperaturesof 1035 �C and 1029 �C, respectively, as obtained using the QUILFprogram of Andersen et al. (1993). The geothermometer proposedby Ridolfi et al. (2010) yields a temperature of 964 �C for latite lava.

The geochemical characteristics of these high-K calcalkalinevolcanic rocks indicate that they formed and evolved in a subduc-tion-related arc at a continental margin, as indicated by enrich-ment in REEs, enrichment in LREEs relative to HREEs, enrichmentin LILEs, depletion in HFSEs, and the locations of representativedata points in tectonic discrimination plots (e.g., Pearce, 1982,1983; Cabanis and Lecolle, 1989; Kuscu and Geneli, 2010).

The post-Eocene volcanic complex in the Abazar district isbounded by two parallel thrust faults (the North Qazvin and Versfaults; Fig. 1). Because the North Qazvin Fault is seismically active(Berberian et al., 1993), it is possible that Eocene and Post-Eocenevolcanic activity was related to movement upon this fault. More-over, Guest et al. (2006) proposed that movement upon Eocenenormal faults contributed to the extension related to the deposi-tion of the Karaj Formation in a sedimentary basin. The authorsalso suggested that Eocene extension was related to strike-slipreactivation of normal faults.

In summary, the Abazar district is a complex volcanic massifthat formed from parasitic fissure eruptions after the main (Eo-cene) volcanism in the Alborz zone related to continental collisionbetween the Iranian and Arabian microplates. The massif recordsthe following magmatic phases (Fig. 12):

(1) shoshonitic magma evolved at depth in the magma chamberby fractional crystallization, also producing latitic and rhyo-litic magma;

Fig. 10. (a and b) Multi-element patterns normalized to MORB (Pearce, 1983), and (c and d) REE patterns normalized to chondrite (Nakamura, 1974) of volcanic samples fromthe study area. Shaded area indicates Eocene volcanics.

Fig. 11. Tectonomagmatic discrimination diagrams showing data of volcanic rocks in the Abazar district. (a) La/10–Y/15–Nb/8 plot (Cabanis and Lecolle, 1989). (b) Th/Yb vs.Ta/Yb plot (Pearce, 1982). (c) Nb/La vs. Ba/La plot (Kuscu and Geneli, 2010). (d) 100Th/Zr vs. 100Nb/Zr plot (Pearce, 1983). Abbreviations: SHO: shoshonite; CAB: calcalkalinebasalt; TH: tholeiite; MORB: mid-ocean ridge basalt; WPB: within-plate basalt.


Fig. 12. Schematic cartoon showing the petrologic and volcanic evolution of the Abazar area, North Qazvin, Iran: (a) basaltic replenishment and the development of adifferentiated magma chamber, with shoshonite at the bottom, latite in the middle, and rhyolite at the top, and accompanying ignimbritic eruptions; (b) effusion ofshoshonitic lavas (and rare basalt); (c) new replenishment of andesitic melts and magma mingling, and effusion of latitic lavas; (d) effusion of andesitic lavas.


(2) the top of the magma chamber was tapped, producing rhyo-litic magma emplaced as ignimbrite during explosivevolcanism;

(3) andesitic magma formed and then mingled with the latiticmagma;

(4) shoshonite, latite, and andesite were erupted as more-or-less viscous lava flows.

Acknowledgments

This study was performed as part of a collaborative researchproject between Imam Khomeini International University (IKIU),Iran; Tehran University, Iran; University of Cergy-Pontoise, France;and University of Paris-Sud, France. Kirsten Nicholson, Juhn Liou,and Bernard Bonin are thanked for their useful suggestions thatgreatly improved the manuscript.

References

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