Ž .Journal of Volcanology and Geothermal Research 85 1998 473–494

Geochemical approach to magmatic evolution of Mt. Erciyesstratovolcano Central Anatolia, Turkey

Biltan Kurkcuoglu a,), Erdal Sen a, Erkan Aydar a, Alain Gourgaud b,¨ ¨Niyazi Gundogdu c¨

a Hacettepe UniÕersity, Department of Geological Engineering, 06532, Beytepe, Ankara, Turkeyb UniÕersite Blaise-Pascal, Centre des Recherche Volcanologiques, UMR 6524, 5 Rue Kessler 63038, Clermont-Ferrand, France

c Lafarge Centre Technique inter-unites, 95 rue Montmurier-BP 70-F-38291 St. Quentin FallaÕier Cedex, France

Abstract

Erciyes stratovolcano, culminating at 3917 m, is located in the Cappadocian region of central Anatolia. During itsevolution, this Quaternary volcano produced pyroclastic deposits and lava flows. The great majority of these products arecalc-alkaline in character and they constitute Kocdag and Erciyes sequences by repeated activities. Alkaline activity ismainly observed in the first stages of Kocdag and approximately first-middle stages of Erciyes sequences. Generally,Kocdag and Erciyes stages terminate by pyroclastic activities. The composition of lavas ranges from basalt to rhyoliteŽ .48.4–70.5 wt.% SiO . Calc-alkaline rocks are represented mostly by andesites and dacites. Some compositional2

differences between alkaline basaltic, basaltic and andesitic rocks were found; while the composition of dacites remainunchanged. All these volcanics are generally enriched in LIL and HFS elements relative to the orogenic values except Rb,Ba, Nb depleted alkaline basalt. 87Srr86Sr and 143Ndr144Nd isotopic composition of the volcanics range between0.703344–0.703964, 0.512920–0.512780 for alkaline basalts and change between 0.704322–0.705088, 0.512731–0.512630

Žfor alkaline basaltic rocks whereas calc-alkaline rocks have relatively high Sr and Nd isotopic ratios 0.703434–0.705468,.0.512942–0.512600 . Low Rb, Ba, Nb content with high ZrrNb, low BarNb, LarYb ratio and low Sr isotopic composition

suggest an depleted source component, while high Ba, Rb, Nb content with high LarYb, BarNb, low ZrrNb and low87Srr86Sr ratios indicate an OIB-like mantle source for the generation of Erciyes alkaline magma. These elemental and ratiovariations also indicate that the different mantle sources have undergone different degree of partial melting episodes. Thedepletion in Ba, Rb, Nb content may be explained by the removal of these elements from the source by slab-derived fluidswhich were released from pre-collisional subduction, modified the asthenospheric mantle. The chemically different mantlesources interacted with crustal materials to produce calc-alkaline magma. The BarNb increase of calc-alkaline samplesindicates the increasing input of crustal components to Erciyes volcanics. Sr and Nd isotopic compositions and elevated LILand HFS element content imply that calc-alkaline magma may be derived from mixing of an OIB-like mantle melts with asubduction-modified asthenospheric mantle and involvement of crustal materials in intraplate environments. q 1998 ElsevierScience B.V. All rights reserved.

Keywords: Erciyes; alkaline calc-alkaline associations; within-plate magmatism; Central Anatolia

) Corresponding author. Fax: q90-312-299-21-36; E-mail: biltan@Jeo-hun.edu.tr

0377-0273r98r$19.00 q 1998 Elsevier Science B.V. All rights reserved.Ž .PII: S0377-0273 98 00067-5

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨474

1. Introduction

Central Anatolia is bordered by three lithosphericcollision areas: NAF—North Anatolian Fault, dex-tral strike-slip; EAF—East Anatolian Fault, sinistralstrike-slip, and Bitlis–Zagros thrust belt. During theOligocene, due to the opening of the Red Sea andGulf Suez, the Arabian plate started to separate from

Žthe African Plate McKenzie, 1972; Cochran, 1981;Izzeldin, 1987; Bayer et al., 1988 and Le Pichon and

.Gaulier, 1988 . This movement continued during theMiocene, with the activation of the Levant transform

Ž .fault Lyberis, 1988; Steckler et al., 1988 . Thisconvergence movement of the Arabian plate relativeto the African plate to the north is the cause of theclosing of a part of Bitlis ocean at the Middle-Upper

Ž .Miocene Sengor and Yilmaz, 1981 . Closing of the¨Bitlis ocean has been followed by Eurasian–Arabian

Ž .collision Sengor, 1980 .¨

Arabian–Eurasian convergence, associated withthickening and shortening of continental crust inEastern Anatolia and escape of the Anatolian block

Žto the west Sengor et al., 1985; Dewey et al., 1986;¨. ŽSuzanne et al., 1990 is even active today Jackson

and McKenzie, 1984; Sengor et al., 1985; Lyberis et¨.al., 1992; Chorowicz et al., 1994 . In addition, this

movement has also been interpreted as the primaryreason for the internal deformation of the Anatolianblock that is represented by pull-apart basins and

Žthrust faults Sengor et al., 1985; Kempler and Gar-¨.funkel, 1991 .

According to the neotectonic evolution fromMiocene to present time, the Aegean region is gov-erned mostly by subduction-related tectonics whilecollision tectonics control the geology and geomor-phology of other sections of the plate boundary.Turkey is located on the collision boundary to theeast of the Aegean arc. Collision volcanism between

ŽFig. 1. Simplified neotectonic map showing the study area and some of the major neotectonic structures modified from Bozkurt and.Kocyigit, 1993 . NAF—North Anatolian Fault, EAF—East Anatolian Fault, BSZ—Bitlis Suture Zone, EF—Ecemis Fault, TGF—Tuz

Golu Fault, DSF—Dead Sea Fault, AGS—Aegean Graben System, CA—Cyprian Arc, White arrows show the sense of plate motion, and¨ ¨the black half arrows the relative motion senser on the faults.

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨ 475

ŽFig. 2. Generalized volcano-stratigraphical column of studied region Ages from: )))) Ayranci, 1969; ))) Innocenti et al., 1975; ))

.Ercan et al., 1994; ) Notsu et al., 1995 .

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨476

Table 1Ž .Major- and trace-element ppm compositions, CIPW norm values and Sr, Nd isotopic ratios of selected samples

Kocdag stage New Erciyes stage

Alk. Bas. Andesite Ignimbrite Basalt Alkaline basaltŽ .Basaltic andesite I

ERC96-116 ERC96-195 ERC96-109 ERC96-112 ERC96-115 ERC96-113 ERC95-64 C88-79 ERC96-145

SiO 49.13 62.10 62.07 60.19 66.49 62.04 51.98 48.39 52.502

Al O 17.14 17.03 17.42 17.18 15.84 16.33 17.07 17.61 17.972 3

Fe O 11.24 5.48 5.10 6.73 4.63 6.52 9.17 9.15 9.192 3

MnO 0.18 0.09 0.08 0.11 0.09 0.11 0.14 0.15 0.15MgO 6.60 2.73 3.07 2.73 1.00 2.11 6.02 8.39 4.65CaO 9.12 5.53 6.65 6.11 3.26 5.03 8.89 11.41 7.52Na O 3.74 3.88 3.37 3.83 4.55 4.39 3.75 3.36 4.172

K O 0.71 2.14 1.37 1.75 3.06 2.04 0.95 0.18 1.602

TiO 1.77 0.82 0.68 1.02 0.84 1.15 1.56 1.37 1.572

P O 0.36 0.19 0.18 0.35 0.22 0.30 0.47 n.a 0.662 5

Total 99.99 99.99 100.00 100.01 99.97 100.00 100.00 100.00 99.99

Qz 0 15.53 18.52 14.1 19.56 15.06 0.5 0 0.16Co 0 0 0 0 0 0 0 0 0Or 4.2 12.47 8.04 10.22 17.32 11.76 5.56 1.06 9.4Ab 31.73 32.32 28.26 31.99 36.89 36.3 31.48 25.6 35.03An 27.92 22.38 28.06 24.23 13.17 18.39 26.7 32.44 25.43Ne 0 0 0 0 0 0 0 1.54 0Di_Wo 6.27 1.43 1.42 1.42 0.39 1.7 5.82 10.09 3.06Di_En 3.97 1 1.02 0.89 0.3 1.09 3.98 7.15 1.97Di_Fs 1.91 0.3 0.27 0.44 0.06 0.5 1.38 2.06 0.89En 2.51 5.7 6.55 5.83 2.1 4.04 10.89 0 9.54Fs 1.2 1.72 1.73 2.86 0.4 1.87 3.78 0 4.31Fo 7 0 0 0 0 0 0 9.63 0Fa 3.7 0 0 0 0 0 0 3.06 0Mt 4.74 3.35 3.15 3.64 3.33 3.8 4.42 4.16 4.44Ilm 3.36 1.54 1.27 1.92 1.52 2.13 2.94 2.6 2.96Hem 0 0 0 0 0 0 0 0 0Ap 0.85 0.45 0.43 0.83 0.5 0.69 1.11 0 1.56

Total 99.37 98.19 98.72 98.37 95.53 97.33 98.56 99.39 98.75

Nb 12.3 11.9 10.2 20.2 18.2 16.8 14.6 6.3 29.8Zr 214.8 198.7 171 234.5 367.8 258.2 228.2 123.6 236Y 29.7 29.7 21 30.8 42 33.8 30.1 22.4 28.6Sr 457.6 334.4 335.4 376.3 253.9 343.3 528.2 398.5 656.9Rb 5.6 77.1 37.1 27.4 97 72.8 13.5 2.3 30.4Ga 23.7 19.4 18.4 22.6 22.1 23.4 22 16.5 23.4Ni 86.89 29.2 38.2 17 5.8 11.4 97.4 106.2 48.5Co 51.5 45.1 44 41.7 51.5 34.4 42.9 35.8 40.7Cr 118.8 16.7 65.9 24.6 4.1 8 178.1 201.2 65.4V 168.7 84.4 90.9 106.2 56.4 119.3 137.4 165.2 159.5Ba 282.6 381.1 289.70 483.4 563.4 456.8 238.1 52.7 507.9

87Srr 0.703964 0.704455 0.704633 0.70334486 Sr "11 "11 "15 "14143Ndr 0.512780 0.512652 0.512720 0.512920144 Nd "11 "10 "7 "9

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨ 477

Ž .Basaltic andesite II Andesite Andesite I

ERC91-13 C88-75 ERC91-3 ERC96-138 ERC95-66 ERC95-8 ERC95-92 ERC96-129

53.57 53.28 54.66 55.08 53.51 61.81 63.98 62.9917.64 17.39 17.81 17.93 16.60 17.90 16.72 16.307.60 8.12 7.29 7.23 8.46 5.06 4.55 5.330.12 0.13 0.11 0.12 0.14 0.08 0.08 0.095.74 6.55 5.72 5.42 6.58 2.28 2.52 2.618.70 7.57 8.50 8.20 8.46 5.80 5.62 5.573.84 4.08 3.54 3.48 3.41 3.85 3.71 3.901.27 1.46 1.05 1.19 1.17 2.22 2.03 2.221.08 1.41 1.00 1.05 1.31 0.81 0.64 0.780.43 n.a 0.32 0.32 0.36 0.21 0.17 0.23

100.00 100.00 100.00 100.02 100.00 100.01 100.03 100.02

1.18 0 4.45 5.53 2.77 15.21 19.18 16.310 0 0 0 0 07.27 8.75 6.15 6.97 6.86 12.77 11.76 12.59

31.48 34.95 29.7 29.19 28.69 31.73 30.72 31.6526.33 25.09 29.36 29.49 26.35 24.4 22.5 19.570 0 0 0 0 05.32 5.39 4.33 3.63 5.42 0.97 1.54 2.293.71 3.91 3.03 2.56 3.79 0.71 1.62 1.621.17 0.99 0.93 0.77 1.17 0.17 0.22 0.47

10.13 9.24 11.09 10.82 12.5 4.82 4.99 4.63.18 2.34 3.41 3.26 3.87 1.14 0.97 1.320 2.36 0 0 0 0 0 00 0.66 0 0 0 0 0 03.7 4.25 3.61 3.68 4.06 3.32 3.09 3.261.99 2.72 1.88 1.98 2.47 1.5 1.2 1.420 0 0 0 0 0 0 00.99 0 0.76 0.76 0.85 0.47 0.4 0.52

96.46 100.63 98.7 98.64 98.8 97.22 97.72 95.63

23.4 16 19 17 11.8 12.9 14.5184.3 204.2 169.5 181.5 195.6 164.8 197.923.6 25 22 22.8 25.8 22 27.1

516.2 496.7 460.4 457.4 482.2 307.4 307.626.6 28.9 23.1 22.2 21.5 62.4 69.819.5 16.3 17.8 19.5 20.8 18.3 19.556 71.9 7.67 69.9 106.2 26.5 19.722.7 n.a 26.1 39.7 45.5 38.2 30.3

102.7 n.a 207.8 117.8 223.1 21.9 26.6118.9 n.a 123.6 125.6 159.4 72.3 85.8338.6 344.3 239.6 284.8 238 348.6 414.2

0.705088 0.704322 0.704666 0.704868"13 "13 "10

0.512630 0.512731 0.512678 0.512631"8 "6 "9

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨478

Ž .Table 1 continued

New Erciyes stage

Ž . Ž . Ž .Andesite II Dacite II Dacite III

C88-80 ERC91-29 ERC96-151 ERC96-175 ERC91-21 ERC95-99 ERC95-100 ERC91-9 ERC96-186

SiO 62.76 57.11 60.96 61.09 65.84 67.03 69.92 65.71 66.582

Al O 16.77 17.57 17.73 17.47 16.29 15.63 14.91 16.18 15.812 3

Fe O 5.07 7.66 5.44 5.52 4.08 3.82 3.21 4.22 3.922 3

MnO 0.08 0.13 0.09 0.09 0.07 0.07 0.06 0.07 0.07MgO 3.23 3.66 3.29 3.30 1.98 1.92 1.14 2.15 2.05CaO 6.08 6.70 6.90 6.79 4.93 4.31 3.29 5.03 5.08Na O 3.57 4.21 3.47 3.48 3.95 3.83 3.81 3.91 3.532

K O 1.80 1.34 1.24 1.36 2.09 2.69 3.04 1.99 2.322

TiO 0.63 1.13 0.69 0.69 0.58 0.53 0.50 0.54 0.502

P O 0.50 0.20 0.22 0.18 0.15 0.12 0.17 0.152 5

Total 100.00 100.00 99.99 100.00 100.00 99.99 100.00 100.00 100.01

Qz 22.02 8.04 16.43 16.28 22 22.59 27.18 21.42 23.66Co 0 0 0 0 0 0 0 0 0Or 12.88 7.8 7.27 7.92 12.29 15.48 17.49 11.46 13.42Ab 32.58 35.2 29.11 29.02 33.26 31.56 31.39 32.24 29.28An 18.47 24.83 28.9 27.63 20.45 17.02 14.23 20.15 20.06No 0 0 0 0 0 0 0 0 0Di_Wo 1.11 2.01 1.56 1.72 1.14 1.18 0.36 1.28 1.53Di_En 0.84 1.27 1.09 1.19 0.89 0.96 0.31 0.96 1.19Di_Fs 0.15 0.62 0.34 0.39 0.13 0.08 0 0.19 0.17En 3.27 7.75 7.03 6.9 4.02 3.7 2.45 4.24 3.81Fs 0.59 3.79 2.2 2.24 0.59 0.32 0 0.83 0.56Fo 0 0 0 0 0 0 0 0 0Fa 0 0 0 0 0 0 0 0 0Mt 2.89 3.8 3.16 3.16 3.02 2.93 2.06 2.94 2.89Hm 0.93 2.13 1.29 1.29 1.1 0.99 0.93 1.01 0.93Hem 0 0 0 0 0 0 0.57 0 0Ap 0.33 1.16 0.47 0.52 0.43 0.36 0.28 0.4 0.36

Total 96.04 98.39 98.85 98.28 99.31 97.17 97.27 97.12 97.85

Nb 5.1 18.7 13.4 11.1 14.5 13.4 15.6 15.4 11.8Zr 127.3 215.8 149.3 177.8 185.7 169.4 187.5 181.1 189.7Y 23.3 29 18.7 19.9 27.3 22.1 22.7 26.1 24.4Sr 401.9 421.7 329.7 364.9 295.2 242.4 212.6 275.3 264.3Rb 1.7 30 35.7 37.9 84.9 95.6 116.3 77.8 87.4Ga 17 20 18.9 17.9 18.3 16.8 17.1 17.9 16.5Ni 111.1 35.8 26 40.2 23.1 17.3 10.4 19.3 27.3Co 44.7 20.7 39 35.1 13.2 41.5 18.8 11.6 25.2Cr 215.6 78.2 38.7 67.9 68.4 18.4 10.4 70.3 51.9V 164.3 119.6 88.9 90.6 69.4 57.1 51.5 57.6 58.4Ba 59.2 312.3 257.8 299.7 396.8 452 501.2 383.8 411

87Srr 0.703434 0.704591 0.70514386 Sr "13 "10 "12143Ndr 0.512942 0.512714 0.512600144 Nd "13 "9 "7

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨ 479

Ž . Ž . Ž .Dacite IV Nuee ardente Rhyodacite I Rhyodacite II´

ERC96-204 ERC95-80 ERC95-83 ERC95-84 ERC96-173 C88-89 ERC95-90 ERC91-28

64.91 66.61 67.06 66.88 70.70 71.24 70.55 70.5016.59 16.07 16.21 16.19 15.09 14.84 15.34 15.204.46 3.99 3.87 3.92 2.64 2.54 2.82 2.810.07 0.07 0.07 0.07 0.05 0.06 0.06 0.062.30 1.71 1.69 1.73 0.89 0.93 0.79 0.965.39 4.61 4.51 4.58 3.21 3.09 3.23 3.213.68 4.00 3.68 3.78 4.30 4.10 3.92 4.001.82 2.27 2.27 2.19 2.78 2.85 2.83 2.790.59 0.51 0.51 0.51 0.34 0.34 0.36 0.370.17 0.15 0.14 0.14 0.09 0.11

99.98 99.99 100.01 99.99 100.00 100.00 99.99 100.00

21.66 22.02 24.58 24.11 26.93 28.59 28.47 28.590 0 0 0 0.04 0.18 0.04

10.64 12.88 13.24 12.77 16.19 16.49 16.37 16.4930.72 32.58 30.72 31.56 35.79 33.85 32.49 33.8523.09 18.47 20.67 20.51 13.47 15.21 15.09 15.210 0 0 0 0 0 0 00.92 1.11 0.19 0.42 0.92 0 0 00.68 0.84 0.14 0.32 0.8 0 0 00.15 0.15 0.02 0.06 0 0 0 04.98 3.27 3.99 3.94 1.39 2.39 1.92 2.391.14 0.59 0.62 0.68 0 0 0 00 0 0 0 0 0 0 00 0 0 0 0 0 0 03.02 2.89 2.9 2.9 1.44 1.85 1.81 1.851.1 0.93 0.95 0.95 0.63 0.7 0.66 0.70 0 0 0 0.59 0.6 0.590.4 0.33 0.33 0.33 0.26 0.21 0.26

98.48 96.04 98.34 98.55 99.97 97.8 99.97

13.3 11.8 9.6 15.7173.8 158.3 167.6 171.723.8 19.8 22 25

257.6 201.7 200.9 210.182.6 110.9 112.7 133.717 14.6 18.1 16.413.4 3.9 5.7 8.232.9 n.a 38.4 5.818.3 n.a 5.7 48.154.9 n.a 31.1 28.9

425.9 440.3 486.3 482.8

0.705309 0.705468"13 "10

0.512589 0.512570"7 "6

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨480

the Afro-Arabian and Eurasian plates occurred mainlyalong a NE–SW direction in Neogene and Quater-

Ž .nary times in Central Anatolia Pasquare et al., 1988 .By virtue of the Anatolian block was operated by thecombine effect of subduction and extensional pro-cesses, different types of volcanic activity can beobserved in central Anatolia. Mt. Erciyes is the mostvoluminous stratovolcano of Central Anatolia, reach-ing 3917 m and it is located approximately 15 km

Ž .south of Kayseri Fig. 1 . It is composed of severalandesitic and dacitic domes, basaltic and basalticandesitic cones, pyroclastic products and their flows.

Origin of the Mt. Erciyes magmatism is now asubject of discussion. Different evolution models,

Žincluding subduction Pasquare, 1968; Innocenti et.al., 1975; Ayranci, 1992 and intraplate activities

Ž .Aydar et al., 1995; Notsu et al., 1995 were pro-posed for the origin of the Mt. Erciyes volcanism.So, Erciyes volcanics are compared with orogenic

Žand extension-related rocks Basin And Range.province, Egan Range, Mojave desert in the later

sections. Basin and Range provinces were developedapproximately east–west tensional stress. These haveresulted in extension with consequent thinning of the

Ž .crust and high heat flow Fitton et al., 1988 . Inaddition, Egan range volcanics and Taos plateauvolcanic field are the open system differentiates. Inthis study, we deal with time integrated geochemicalevolution of Mt. Erciyes alkaline and calc-alkalinemagmas. An evolutionary model is suggested for thegeneration of these volcanics based on the new

Žgeochemical major, trace and REE concentrations,.Sr and Nd isotopic ratios data.

2. Sampling and analytical methods

The samples used in this study were collected in1995 and 1996 and chosen according to thevolcano-stratigraphic units. However, a few samples

Ž .have come from Kurkcuoglu 1994a and from the¨ ¨Ž .study of Aydar et al. 1995 .

Major and trace element compositions were deter-mined, using a Philips PW 1480 X-ray fluorescencespectrometer, from the fused glass tablets and pressedpowdered samples, respectively, at the GeologicalEngineering Department of Hacettepe University,Ankara. The spectrometer is calibrated by using

USGS and Geostandards. Rare earth element analy-ses were performed using a JY7011 Inductively Cou-

Ž .pled Plasma ICP spectrometer and Sr and Nd iso-topic compositions were determined in a fully auto-mated V.G. isomass 54E mass spectrometer at theDepartment of Geology, Blaise-Pascal University,

Ž .Clermont-Ferrand France . Analytical error are typi-cally "2% for major elements and less than "10%for trace elements. The 87Srr86Sr ratios are nor-malised to 86Srr88Srs0.1194. The 143Ndr144 Ndratios are normalised to 146 Ndr144 Nds0.7219. Overthe periods of measurements, replicate analyses of

Ž .standards gave, National Bureau of Standards NBS87 86 Ž .987, Srr Srs0.71024"4 2s and, for La jolla,

143 144 Ž .Ndr Nds0.51184"3 2s .

3. Geology of Mount Erciyes stratovolcano

Mt. Erciyes is situated approximately 15 km southof Kayseri and the products are distributed in largeareas. A volcano-stratigraphical column of the stud-ied region is given in Fig. 2. The volcanologicalevolution of Mt. Erciyes can be examined in two

Ž .main parts: Kocdag and New Erciyes Stages Fig. 2 .Kocdag is mainly composed of lava flows of alkalinebasalt, andesite and basaltic andesites. They consti-tute the eastern flank of the Mt. Erciyes volcaniccomplex. The first explosive activity is the

Ž«Valibaba» ignimbrite eruption, 2.8 Ma ago In-.nocenti et al., 1975 and this eruption was followed

by a caldera collapse.The new Erciyes stage represents different basaltic

andesitic, andesitic, dacitic, rhyodacitic lava genera-tions and associated pyroclastics. The volcanic prod-ucts are related to central and adventive monogenetic

Ž .vents domes and cones . The last dated eruptionŽ .0.083 Ma; Notsu et al., 1995 corresponds to thefourth dacitic lava generation in the volcano-strati-

Ž .graphical column Fig. 2 . The emplacement of thepyroclastics prior to rhyodacitic dome and debrisavalanche deposits is the best known and most recentproducts of the volcano.

4. Major-element geochemistry

Major- and trace-element data are shown for se-lected samples and are given in Table 1. Kocdag and

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨ 481

Erciyes volcanics are generally calc-alkaline in char-Ž .acter but some alkaline affinities Kurkcuoglu, 1994a¨ ¨

Žhave been observed between basaltic rocks Le Bas. Ž .et al., 1986 Fig. 3 . Alkaline basalt were found at

the base of Kocdag volcanics whereas the same rockŽ .types were placed at the basaltic andesite II stage

of Erciyes section. These alkaline basaltic rocksshow some chemical differences. Alkaline basalt ofKocdag and Erciyes volcanics have high Fe O ,2 3

MgO and TiO content whereas alkaline basic prod-2

ucts of Erciyes suite have higher content of Na O,2

K O and relatively higher content of Al O . Alka-2 2 3

line and sub-alkaline behaviour which is observed atthe alkaline samples on Na O and K O variations2 2

diagrams they were interpreted as transitional basaltsŽbetween alkaline and tholeiitic series Middlemost,

. Ž .1975 Fig. 4 . Alkaline basaltic products of Erciyessequence can be separated in two main parts on thebasis of chemical compositions. Alkaline basalticrocks differ from alkaline basalts by low MgO, CaOand high K O content.2

The great majority of calculated CIPW norm val-Ž .ues Table 1 of Erciyes volcanics, are quartz norma-

tive some alkaline basaltic rocks are nepheline andŽ .olivine normative Kurkcuoglu, 1994a . This situa-¨ ¨

tion also supports the possibility of transitional seriesbetween basaltic rocks.

Ž .Harker diagram Fig. 5 of Kocdag sequence andErciyes volcanics reveal that Fe O , MgO, MnO and2 3

CaO content correlate linearly and negatively whileNa O and especially K O content correlate posi-2 2

tively with SiO . Ignimbrites of Kocdag sequence2

have higher Na O and K O content than all other2 2

silica saturated volcanics. Al O content of basaltic2 3Žrocks alkaline basalt, basalt, basaltic andesite I and

.II increases with increasing SiO and decreases for2

calc-alkaline samples. These trends can be explainedby separation of plagioclase and ferro-magnesianphases from the liquid by fractional crystallisation.Correlation of TiO –SiO is slightly different from2 2

the others; TiO content of basaltic rocks steeply2

decrease with increasing SiO whereas evolved rocks2

have a relatively smooth evolutionary trend.During the evolution of the Kocdag and Erciyes

stages, several episodes of volcanic activity espe-cially basaltic andesites, andesites and dacites have

Ž .Fig. 3. Total alkaline–silica diagram of Erciyes volcanics dashed line separates alkaline and sub-alkaline sections, from Miyashiro, 1978 .

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨482

Ž .Fig. 4. SiO –Na O and SiO –K O diagrams of basaltic samples from Middlemost, 1975 .2 2 2 2

Žbeen repeated within the wide time interval 2.544–.0.083 Ma in Notsu et al., 1995 .

Even though compositional differences do notshow great differences between the same episodes ofearly and late stage activities, some compositionaldifferences must be considered. Alkaline activities ofthese two stages have the same major element com-positions. The comparison of andesitic compositionsof Kocdag sequence and Erciyes volcanics indicates

Ž .that the last stage of andesitic activity andesite IIŽ .may be more primitive than older Kocdag andesites

Ž .high MgO, CaO, Cr, Ni .The Erciyes sequence is represented by 2 episodes

of basaltic andesitic activity. The latest is generallyricher in MgO, Fe O , TiO and Zr, Ni, Co, Cr2 3 2

compared to the previous stage.

Dacites of Erciyes sequence do not show majordifferences during their development. On the otherhand, Al O , TiO , Na O and K O content of2 3 2 2 2

Erciyes volcanics are generally higher than the oro-Ž .genic andesites Gill, 1981 , at a given silica content.

5. Trace and REE geochemistry

Trace and REE element data are presented inTables 1 and 2. Erciyes volcanics are generallyenriched in all LIL and HFS elements, relative toN-type MORB. These volcanics are also enriched insome HFS elements such as Nb, Zr, La, Ce and Ni,

Ž .Cr relative to orogenic volcanic rocks Ewart, 1982 .

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨ 483

Fig. 5. Major-element variation diagrams of the Erciyes volcanics. Symbols are the same as in Fig. 3.

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Table 2Ž .Rare earth element determinations for selected samples ppm

ERC96-116 ERC96-115 C88-79 ERC95-64 ERC91-3 ERC91-13 C88-75 ERC95-8 ERC91-29 ERC91-21 ERC95-83 ERC96-173

La 16.4 25.3 5.65 19.7 23.9 31.8 24.9 24.5 27.9 25.9 20.3 25.3Ce 36.9 50 15.1 41 47.7 56 50.1 47.8 55.9 48.5 37.4 46.3Pr n.a n.a 1.95 n.a 4.31 5.92 5.22 n.a 5.08 n.a n.a n.aNd 18.4 24.3 10.7 19.4 20.7 24.5 23.6 17.9 24.3 19.1 14.8 16.2Sm 4.45 4.73 2.87 4.32 3.62 4.11 4.98 3.83 4.75 3.81 2.82 3.05Eu 1.41 1.1 1.2 1.3 1.2 1.38 1.54 0.93 1.4 0.83 0.64 0.59Gd 4.93 4.54 3.84 4.56 3.84 4.23 4.89 3.61 4.57 3.77 3.08 2.94Dy 4.7 4.77 3.83 4.11 3.7 3.75 4.34 3.42 4.59 3.55 2.69 2.73Ho n.a n.a 0 n.a 0 0 0 n.a 0 n.a n.a n.aEr 2.69 2.9 2.44 2.39 2.22 2.24 2.46 1.86 2.57 1.96 1.56 1.63Yb 2.82 2.81 2.28 2.43 2.12 2.19 2.42 1.98 2.58 2.1 1.84 1.89Lu 0.41 0.39 0.34 0.33 0.31 0.33 0.37 0.3 0.4 0.33 0.29 0.31

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨ 485

Fig. 6. Trace-element variations of Erciyes volcanics. Symbols are the same as in Fig. 3.

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨486

ŽFig. 7. Chondrite-normalised spider plots for representative samples from Erciyes volcanics. References taken from Hickey et al., 1986 forAndes and McMillan and Dungan, 1986; McMillan and Dungan, 1988; Feeley and Grunder, 1991 for Taos plateau volcanic field and Egan

.range volcanic complex, Nevada, USA, for Basin and Range Provinces .

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨ 487

It is conventionally observed, correlation of in-compatible elements with SiO reveal that Ba and2

Ž .Rb Fig. 6 amount of volcanics increase with in-creasing SiO , whereas the Sr content decreases. Nb,2

Zr, Y behave compatibly with basaltic rocks andthese elements approximately constant with increas-

Ž .ing SiO for andesitic and dacitic samples Fig. 6 .2ŽAll these variations are partially consistent for calc-

.alkaline rocks plagioclase and clinopyroxene frac-Ž .tionation Kurkcuoglu et al., 1994b . On the other¨ ¨

hand, different incompatible elements variations ob-served between alkaline basic rocks suggest dissimi-lar mantle sources.

These distinct source components can simply bespecified on the basis of trace element contents.

Ž .1 Basic rocks have impoverished Rb, Nb, Ba,high Ni content and Mga may originated from de-

Ž apleted mantle source Nis106.2 ppm, Mg s64.5

Ž . a Ž ..C88-79 ; Nis86.89, Mg s53.77 ERC96-116Ž ..are close to the mantle values of Gill 1981 .

Ž .2 Basic rocks with high Rb, Nb and Ba contentmay be derived from an enriched mantle source.

Ž .3 Moderate concentration of LIL and HFS ele-ments in calc-alkaline rocks, related to an other,possibly continental source component.

Ž .4 In addition, Ba, Nb and Rb depletion and highNi and Cr content are also observed in second stage

Ž .andesites andesite II of Erciyes sequence.Chondrite-normalised spider diagram of Erciyes

volcanics show that basaltic and andesitic productsŽ .have similar trace element signatures Fig. 7A . Rb

depletion can be observed in alkaline basalt relativeto other alkaline and calc-alkaline rocks. On theother hand, dacitic rocks show Rb and K enrichment

Ž .and P, Ti depletion Fig. 7A . The chondrite-normal-ised spider diagrams reveal that Erciyes basalts and

ŽFig. 8. Chondrite-normalised rare earth element patterns of the selected samples Egan Range: Feeley and Grunder, 1991; Taos: McMillan.and Dungan, 1986; Egan Range: Feuerbach et al., 1993 .

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨488

andesites are greatly enriched in LIL and HFS ele-Žments, as compared to lower continental crust Taylor

.and McLennan, 1985 .Alkaline basalts of Erciyes volcanic suite are

different from chondrite-normalised OIB signatureby Rb, Nb, P depletion and Sr and Zr enrichmentand these rocks also differ from Andean samples by

Ž .Nb, Zr and Ba enrichment Fig. 7B . Nevertheless,alkaline basaltic rocks give OIB-like elemental sig-nature and chondrite-normalised trace element pat-tern of that, is similar to basaltic products of the

Ž .Basin and Range provinces Fig. 7C .Similar trace element signature is observed be-

tween calc-alkaline rocks of Erciyes suites and Taosplateau volcanic field, Egan range volcanic com-

Ž .plexes east central Nevada, USA . Ba, Rb, K isenriched in the Taos plateau volcanic field andesitesŽ .Fig. 7D . Dacites have approximately the same

Ž .chondrite-normalised signatures Fig. 7E in both ofErciyes and Egan range suites.

Chondrite-normalised REE pattern of Erciyes vol-canics reveal that LREE enrichment appeared in alltypes whereas HREE have a relatively flat trendŽ .Fig. 8A . LREE content of Erciyes samples are

Ž60–90 times higher than the chondritic values Fig..8 .

Ž .Calculated LarYb ratio Nakamura, 1974 changebetween 2.47–5.81 and 10.18–14.52 for alkalinebasalts and alkaline basaltic rocks respectively. Theseratios and chondrite-normalised spider diagrams re-flect that alkaline basalts and alkaline basaltic rocksare originated from two chemically distinct mantlesource components and also reflect different partialmelting degrees.

In addition, alkaline basalt and alkaline basalticrocks differ from each other by dissimilar chondrite-

Ž .normalised REE patterns Fig. 8 . Alkaline basalticrocks resemble to the Basin and Range provinceswhile calc-alkaline rocks resemble to the Egan Range

Ž .volcanic complex Fig. 8D .

87 86 143 144 ŽFig. 9. Srr Sr and Ndr Nd–SiO diagram of Erciyes volcanics symbols are the same as in Fig. 3; arrows indicate increasing2.degree of fractional crystallisation and crustal contamination .

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨ 489

6. Isotope geochemistry

Sr and Nd isotopic ratios were obtained for se-lected samples and listed in Table 1. Sr and Ndisotopic compositions change between 0.703344–0.705468 and 0.512942–0.512442 values, respec-tively, and these compositions are well correlatedwith SiO . Increasing of 87Srr86Sr and decreasing of2143Ndr144 Nd ratios with increasing SiO imply an2

Ž .AFC process De Paolo, 1981 for the generation ofŽ . 87 86calc-alkaline volcanics Fig. 9A,B . Low Srr Sr

and high 143Ndr144 Nd and low Nb, Ba and Rbcontent suggest an depleted mantle source for gener-ation of alkaline basalts, nevertheless, alkalinebasaltic rocks have slightly high 87Srr86 Sr,143Ndr144 Nd ratios and high Ba, Nb, Rb content.This implies, these lavas may be derived from en-

Ž .riched OIB-like mantle source region. Although, itis impossible to completely discarded the effect ofcrustal contamination process, alkaline basic rockswith high Rb, Nb, Ba content and trace elementsignature similarities with Basin and Range ProvincesŽ .Fig. 7C suggest, isotopic variations of these rocksto be inherited from heterogeneities within theirsource region. In addition, these different sourcecomponents were effected for the generation ofcalc-alkaline magma suite. Mantle-derived rocks withlow 87Srr86Sr, high 143Ndr144 Nd ratio and high Ni,Cr, and low Ba content are seem to be partially ornon-interacted with an other source component. Nev-

ertheless, high 87Srr86Sr and low 143Ndr144 Nd ra-tios are the good indicators of the contaminatedcalc-alkaline magma of Erciyes suite and these val-

Ž .ues are close to the Bulk Earth Fig. 10 . Hence,87 86 143 144 Ž .Srr Sry Ndr Nd Fig. 10 diagram demon-strates that, these rocks could be produced by theinteraction of these different sources.

7. Discussion and conclusion

The geochemical and isotopic data presented hereindicate that different mantellic and continentalsource components have participated to the genera-tion of the alkaline and calc-alkaline products ofErciyes volcanic suite. Alkaline basalt and basalticrocks of volcanics have depleted and OIB-like geo-

Ž .chemical signatures respectively Fig. 10 , whereaschemical characteristics of calc-alkaline samplesŽ 87 86 143 144 .high Srr Sr and low Ndr Nd are close to

Ž .that of the crustal values Fig. 10 .

7.1. The role of asthenospheric mantle source

Alkaline basalts have high ZrrNb, YrNb andlow LarYb and CerY ratios, compared to the otheralkaline basaltic rocks. ZrrNb ratio increases withthe increasing degree of partial melting. In addition,ZrrNb ratio reflects the scale of the Nb anomaly and

ŽCerY is a measure of LREE enrichment Fitton et

87 86 143 144 ŽFig. 10. Isotopic variations in Srr Sr vs. Ndr Nd References from Ito et al., 1987; Chen et al., 1991; Miller and Miller, 1991;.Chaffey et al., 1989, BEsBulk Earth; EM IsEnriched Mantle I; EM IIsEnriched Mantle II .

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨490

Ž ŽFig. 11. CerY–ZrrNb diagram of the selected lava samples References from Chaffey et al., 1989; West et al., 1992, direction of arrow.indicate increasing degree of partial melting . Symbols are the same as in Fig. 3.

.al., 1988 . Ce and Nb, are respectively, more incom-patible than Y and Zr in normal mantle phases;hence, partial melts from the mantle must show

Žnegative correlation between these two ratios Fig..11 These ratio relationships, depleted incompatible

and rare earth element content, low Sr and high Ndisotopic compositions of these rocks suggest, highdegree partial melting of an depleted asthenosphericsource, that is the main aspect for the generation ofalkaline basalts. On the other hand, the depletion ofBa, Nb and especially Rb, in alkaline basalts andandesitic samples of Erciyes volcanic suite may beexplained by the interaction of asthenospheric mantlewith subduction-related fluids and melts, because

this source can be hydrated by subducting slab,stabilizing Nb-Ta-bearing phases. The flux of hydrat-ing fluids passing through this mantle might haveremoved Ba and Rb, resulting in depletion in these

Ž .elements Leat et al., 1988 .Alkaline basaltic rocks are chemically different

from depleted alkaline character, low ZrrNb, YrNband high CerY, LarYb, BarY ratio, enriched na-ture of LIL and HFS elements, low Sr and high Ndisotope ratios may imply low degree partial meltingprobably OIB-like mantle source for the generationof alkaline basaltic rocks. Chemically, the alkalinerocks are resemble Basin and Range basalt whichwere derived from an asthenospheric source and they

ŽFig. 12. YrNb–ZrrNb diagram of selected samples from Erciyes UC: Upper crust; LC: Lower crust, direction of arrow indicate increasing.degree of crustal contamination and depleted mantle source; References from Chaffey et al., 1989 . Symbols are the same as in Fig. 3.

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨ 491

have not been significantly contaminated by litho-Žspheric mantle or crustal materials Menzies et al.,

1983; Fitton et al., 1988, 1991; Kempton et al.,.1991 .

Ž .ZrrNb–YrNb Fig. 12 diagram demonstratepossible interaction of the two different source com-ponents. Distinct LIL and HFS element content,different isotopic and elemental variations indicate tointeraction between depleted asthenospheric meltsand OIB-like mantle source for the generation ofthese alkaline and partly calc-alkaline rocks. Partialmelts derived from these different asthenosphericsources must be interacted with crustal materials togenerate calc-alkaline magma of Erciyes suite.

It is undoubtedly clear that, these different mantlesources have undergone different degree of partial

melting, contributed by different elemental ratios andisotopic signatures.

7.2. Contribution from lithospheric mantle andcrustal contamination

Partial melting is one of the effective processesfor the generation of the of Erciyes volcanics. Inaddition, increasing degree of partial melting may beincreased addition of crustal components to the Er-ciyes volcanics, hence the elevated LIL and HFSelement concentrations can be observed in calc-al-kaline samples.

Interaction of different source components areclearly observed at 87Srr86Sr and 143Ndr144 Nd–

Ž .LarNb diagram Fig. 13 . Increase in BarNb ratio

87 86 143 144 Ž .Fig. 13. Srr Sr and Ndr Nd vs. LarNb OIB from Chaffey et al., 1989 .

( )B. Kurkcuoglu et al.rJournal of Volcanology and Geothermal Research 85 1998 473–494¨ ¨492

indicates increasing lithospheric input into mantlederived OIB-like magma suggested by Fitton et al.Ž .1991 .

As would be expected, Ba, Rb and Nb concentra-tion of the calc-alkaline rocks are relatively high, inaddition, increased Sr and diminuend Nd isotopicratios suggest an interaction between depleted as-thenospheric melts with enriched source componentsand the continental crust. Calc-alkaline rocks are theopen system differentiates of alkaline basic magma.

Ž .McMillan and Dungan 1988 concluded that Taosplateau calc-alkaline andesite and dacite are opensystem differentiates of low- to medium K O olivine2

tholeiitic parent magmas, on the other hand, similarisotopic and trace element signature of alkaline andcalc-alkaline products of Erciyes volcanic rocks tes-

Žtify the alkaline and calc-alkaline associations C88-.79s48.4 wt.% SiO ; C88-80s62.76 wt.% SiO .2 2

Some of calc-alkaline andesite have no crustal in-volvement and trace element content is inherited

Žfrom mantle source region; however, AFC De Paolo,.1981 is the major process of the production of

calc-alkaline magma of Erciyes suite. Evolved rocks,especially dacites, are the most contaminated sam-ples according to the Sr and Nd isotopic composi-

Ž .tions Fig. 10 .Three different source components are the main

aspects of generation of the Erciyes magmatic suite.Mixing of depleted asthenospheric mantle melts withOIB-like magma and contamination of the ascendingmagma with local crustal materials and progressivefractional crystallisation may produced the LIL andHFS element enriched calc-alkaline rocks of Erciyesand Kocdag volcanics.

Ž .Harris et al. 1986 proposed that continental col-lision is preceded by the subduction of oceanic litho-sphere and the subducted slab remains under thethickened crust during the syn-collision stage. Dur-ing the tectonic evolution of Anatolian block, priorto late Eocene, two oceans existed to the north of theArabian platform and to the north of the Anatolidesand the oceanic crusts were subducting northward

Ž .from both oceans Sengor and Kidd, 1979 . This¨suggests that slab-derived fluids that is able to mod-ify the asthenospheric mantle sources, may surviveunder the thickened crust, but not largely contributedto magmatic evolution of Erciyes volcanic rocks. Onthe other hand, Central Anatolia is dominated by

northeast-southwest shortening and northwest–south-Ž .east extension Sengor et al., 1985 which leads¨

magmatic activity and open system differentiation ofascending magma.

All of the geochemical data suggest an intraplateorigin for Erciyes stratovolcano as a result of thepost-collisional extension in the Anatolian plate.

Acknowledgements

This study was financially supported by HacettepeUniversity, The Scientific and Technical Research

Ž . ŽCouncil of Turkey TUBITAK , French CNRS PICS.no. 206 and French Embassy in Ankara. We are

grateful to Dr. Willam Wilson and Dr. Gilles Chazotfor their constructive comments. We also thankAbidin Temel for providing X-Ray Flourescence fa-cilities and Pinar Alici for useful suggestions. Theauthors thank Attila Ciner for useful corrections ofthe earliest version of manuscript.

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