GEOCHEMICAL CHARACTERISTICS OF THE LAVA DOMES IN YATAGAN VILLAGE AND SAĞLIK TOWN , FROM ERENLERDAGI ( KONYA , CENTRAL TURKEY ) VOLCANITES

Geochemical data shows that all samples are high-K calc-alkaline, mostly metaluminous, and rhyodacite to andesite in composition. They are characterized by an enrichment in Large Ion lithophile Elements (e.g. Cs, K), and a depletion in High Field Strength Elements (e.g. Ti, Y). In Harker variation diagrams, SiO2 increases with increasing K2O, Na2O, Rb, Th, U, Nb, Zr contents; and decreasing TiO2, FeOt, MgO, CaO contents, suggesting fractional crystallisation of hornblende (± pyroxene, olivine) and titanite. The REE pattern of the samples shows an enrichment in Light Rare Earth Elements, and a depletion in Heavy Rare Earth Elements, resultant with high [(La/Lu)N= 8.2-18.0] ratios. Existence of slight Eu anomaly (Eu/Eu*: 0.66-0.80 ) may suggest plagioclase fractionation in the samples.


INTRODUCTION
Turkey is located on the Alpine-Himalayan orogenic belt and occupies a zone of convergence between two major plates, Eurasia and Afro-Arabia.The Anatolian region has been created by the amalgamation of smaller continental fragments that were formerly sited at the northern margin of Gondwana during late Palaeozoic and early Mesozoic times.Along the Miocene thrust front, collision of Eurasian and Arabian plates induced deformation of the Anatolian plate, and produced various volcanic rocks covered an area of about 85,000 km 2 in East, Central and West Anatolia [1].Acccordingly, young volcanic provinces, such as Galatia Volcanites (GV), Central Anatolian Volcanites (CAV) and Konya volcanites (KV), cover large areas In Central Anatolia.
The study area (Figure 1) is located approximately 50 km to the west of Konya (Central Anatolia).Radiometric studies suggest that the volcanic activity was initiated at 11.9 Ma and ended 3.5 Ma [2].In the area, a limited number of studies related to the Konya volcanics have been done [2] [3][4] [5] [6] [7] [8] [9].However, there is no study involving geochemical characteristics of the lava domes in the study area in detail.Hence, it is aimed to determine geochemical characteristics and petrogenesis of the Miocene lava dome at Yatagan and Saglik area.

GEOLOGICAL SETTING
The study area is made up of volcanic, sedimentary and volcano-sedimentary units (Figure 1).The basement rocks of the study area are characterized by pre-Miocene ophiolitic complex, schist, quartzite and dolomitic limestone [2], which are overlain uncomformably by volcanic rocks.Based on the stratigraphic and radiometric age determination of volcanic rocks, it was suggested that Sille volcanics are the first volcanic phase [2] [10].This unit underlied the sedimentary and volcano-sedimentary rocks, which are overlain by Kiziloren, Bulumya, Detse and Sadiklar ignimbrites, nuee ardentes and andesitic-basaltic lava and dome (Figure 1).The lava domes are located, more or less, at the center of Erenlerdagi volcanism, along with a line trending in NW-SWW direction.Upper Pliocene limestone and Quaternary fluvial and alluvium materials cover all the units.Within the lava domes, there are a few rock quarries at Yatagan and Saglik area (Figure 2), in where mafic-and felsic magma interactions can be clearly observed.Mafic micrograined enclaves (MME) in the lava range in size from a few cm to a few meters, and shapes from angular to elips/rounded, with well-developed chilly zone.The samples were collected at the quarries, opened within the lavas, to determine to the geochemical characteristics of the lava domes.

SAMPLING AND ANALYTICAL METHODS
About 50 thin-sections from the lava domes were examined petrographically.Of these, selected samples were analysed for minerals and whole-rock major, trace and REE.Whole rock analyses for major and trace elements were carried out with Inductively-Coupled Plasma Emission Spectrometer from pulps after 0.2 g rock-powder were fused with 1.5 g LiBO 2 and then dissolved in 100 mm3 5% HNO3 at ACME Analytical Laboratories Ltd., Vancouver, Canada.The REE contents were determined by Inductively-Coupled Plasma Mass Spectrometry from pulps after 0.25 g rock-powder was dissolved with 4 acid digestions at ACME (Canada).Analytical uncertainties vary from 0.1% to 0.04% for major elements; from 0.1 to 0.5% for trace elements; and from 0.01 to 0.5 ppm for rare earth elements.
The plagioclase crystals (0.6-3.2 mm) are mostly subhedral and show albite-carlsbad twinning, oscillatory zoning and sieve texture.Sericitisation and sousuritisation are common alteration types in the plagioclase.The amphiboles (0.4-3.0 mm) show strong pleochroism in the shades of yellowish brown to reddish brown colour, with plagioclase inclusions.It is altered to an aggregate of opaque mineral, chlorite and epidote (0.6 mm).The biotite forms as subhedral laths shows strong pleochroism, from light to dark brown.It is replaced to amphiboles, and mostly surrounded by a reaction rim composed of plagioclase, epidote and quartz.The quartz 10 phenocrysts (0.4-2.0 mm) is subhedral and sometimes resorbed.The pyroxene occurs only in a few samples, and typically has no color.40A-1b (Cross Nicols).Bt: biotite, pl: plagioclase

Major and trace elements
Results of the bulk rock chemical analyses are given in Table 1.The samples are calcalkaline, high-K calcalkaline and metaluminous in composition (Figure 4a, b, d).However, Erenlerdagi volcanics as a whole range in composition from calc-alkaline through High K calc-alkaline to shoshonite (Figure 4c).In Figure 5a, the samples are plotted clearly in both andesite and dacite areas while the samples are found on basalt/basaltic andesite and dacite/rhyolite areas in trace element nomenclature diagram (Figure 5b).In Harker variation diagrams (Figure 6), SiO 2 increases with decreasing TiO 2 , Al 2 O 3 , FeOt, MgO and CaO, suggesting fractional crystallization of amphibole (±olivine, ±pyroxene), ilmenite/titanomagnetite.SiO 2 also shows negative correlation with Eu/Eu*, Sr (Figure 7), suggesting plagioclase fractionation.Existence of negative correlation between SiO 2 and V also confirm titanomagnetite fractionation in the samples.SiO 2 shows however, a negative correlation with both K and Rb, possibly due to biotite being remained in the melt.

GEOTECTONIC SETTING
The samples have low-intermediate Nb (11-15ppm), Zr (134-175 ppm), Y (17-25 ppm), and TiO 2 (0.43-0.0.83 wt %) contents, which is typical for calc-alkaline associations.Low La/Th (1.5-2.4) and intermediate-high Ba/Nb (38-95) ratios in the samples are also caracteristics for subduction-related magma [19].High Ba/Th ratio in the samples, mostly >450, also show similarity to the orogenic magmatism [20] Geotectonic diagrams for granites are used to constrain the tectonic setting of the samples, as their composition ranges from rhyolite, through dacite to andesite.In diagrams of [21], the samples are situated mostly on Active Continental Margin areas (Figure 9a, b).All samples are plotted on the fields of Volcanic Arc Granitoids and Post orogenic granite in Figure 9c,d.In a Hf-3Ta-Rb/30 ternary diagram, the samples are found both on the areas of Volcanic Arc Granitoids and Late-post colision granite (Figure 9e).

DISCUSSION & CONCLUSIONS
Geochemical data suggests that the crystal fractionation played a significant role in the genesis of the volcanic rocks during ascending of a homogeneous magma.Existence of various MMEs in the volcanics also suggests that magma mixing/mingling processes affected on the chemical composition of the samples.All samples are metaluminous in composition, with ASI values < 1.1, suggesting an igneous source.Therefore, the lava samples could have been formed by partial melting of an igneous source (basic rocks) coupled with contamination and fractional crystallization of amphibole (±olivine, ±pyroxene), ilmenite/titanomagnetite in relation with the subduction of the African plate underneath the Anatolian plate during Miocene.Tatar et al.(2002) also suggest that the oldest Sille volcanics (11.7-11.4Ma) rotated anticlockwise during early stages of crustal thickening and deformation before later Miocene episode (c.10.9-8.9Ma, D=183 o , I= -47 0 ) and a Mio-Pliocene episode (D=179 0 , I= -51 0 ).
The samples were usually enriched in LILE, and depleted in HFSE, similar to the arc magmatics [25], [26].Calc-calkaline character of the samples are also in accordance with this suggestion.However, existence of trachyandesite composition of the samples, with late-postcolliginal tectonic setting on the geotectonic setting may suggest that the samples might have been affected by extensional tectonics after contraction regime.The samples may thus represent late/postcolligional volcanism in the area.

Figure 1 :
Figure 1: The location and the geologic map of the study area (Modified from [2]).

Figure 2 :
Figure 2: A rock quarry of lava dome at west of Sağlık area.

Figure 6 :
Figure 6: Major oxide variation diagram of the samples, and their correlation coefficients

Figure 7 :Figure 8a :
Figure 7: Harker variation diagrams of some trace element, with their correlation coefficients

Figure 8b :
Figure 8b: Chondrite normalized rare earth element patterns of the samples.Normalizing values are from [18] Figure 9a:

Table 1 :
Major, trace and rare earth element analyses of the samples.