Petrographic and geochemical analyses of Early Miocene volcanic units in the Bigadiç borate basin, western Anatolia-Turkey: evidences of magma mixing/mingling processes

Yıl 2010, Cilt: 31 Sayı: 2, 141 - 168, 01.03.2010

Fuat Erkül Sibel TATAR Erkül Cahit Helvacı

Öz

Anahtar Kelimeler

-

Erken Miyosen Bigadiç bor havzasındaki volkanik birimlerin petrografik ve jeokimyasal özellikleri: magma karışımının kanıtları, Batı Anadolu-Türkiye

Öz

Batı Anadolu’daki Senozoyik yaşlı alkali ve kalkalkali karakterli volkanizmanın en iyi gözlendiği bölgelerden birisi kuzeydoğu doğrultulu Bigadiç bor havzasıdır. Bazalttan riyolite bileşim gösteren volkanik kayaçların oluşum yaşları 23-17.8 milyon yıl arasındadır. Bigadiç çevresinde, temel kayaçlar üzerindeki Erken Miyosen yaşlı istifler gölsel, flüvyal ve evaporitik tortullar ile bunları kesen kuzeydoğu doğrultulu volkanik çıkış merkezlerinden üretilen lav ve volkaniklastik kayaçlar ile temsil edilmektedir. İki farklı evrede gelişen bu volkanik birimler litolojik, petrografik ve bileşimsel özelliklerine göre, Kocaiskan volkanik birimi, Gölcük bazaltı, Sındırgı, Kayırlar ve Şahinkaya volkanik birimleri olmak üzere beş birim altında incelenmiştir. Gölcük bazaltı hariç, diğer tüm volkanik birimlerde yaygın olarak görülen yuvarlağımsı elipsoidal anklavların boyutları birkaç milimetreden birkaç santimetreye kadar değişmektedir. Kalkalkali bileşim sergileyen Kocaiskan, Sındırgı, Şahinkaya ve Kayırlar volkanik birimleri orta-yüksek, hafif alkali bileşimli Gölcük bazaltı ise yüksek K’ludur. Kalkalkali birimlerin nadir toprak element dağılım desenleri birbirlerine benzerlik göstermektedir. Bu birimler hafif nadir toprak elementlerince zenginleşme gösterirken, hafif alkali bileşimli Gölcük bazaltında ise daha az zenginleşme görülmektedir. Eu anomalisi Kocaiskan ve Sındırgı volkanik birimlerinde, Şahinkaya, Kayırlar ve Gölcük birimlerine göre daha belirgindir. Bigadiç ve çevresinde eş yaşlı alkali-kalkalkali birlikteliği ile karakterize bimodal volkanik kayaçların oluşumunda, magma karışım süreçleri etkili olup, kabuksal kökenli ve manto kökenli iki farklı magma kaynağı etkindir

Anahtar Kelimeler

Bigadiç, hafif alkali-kalkalkali, kabuksal kökenli ve manto kökenli magma kaynağı, karışım dokuları, mafik mikrogranüler anklav, Miyosen

Kaynakça

• Akay, E., and Erdoğan, B., 2004. Evolution of Neogene calc-alkaline to alkaline vol- canism in the Aliağa-Foça region (wes- tern Anatolia, Turkey). Journal of Asian Earth Sciences, 24, 367-387.
• Aldanmaz, E., Pearce, J.A., Thirlwall, M.F., and Mitchell, J.G., 2000. Petrogenetic evo- lution of late Cenozoic, post-collision volcanism in the western Anatolia, Tur- key. Journal of Volcanology and Geot- hermal Research, 102, 67-95.
• Alpaslan, M., 2001. Volkanik kayaçlarda mag- ma karışım dokuları ve mekanizmaları, D. Boztuğ ve N. Otlu (editörler), Mag- matik Petrojenez, TÜBİTAK Lisansüstü
• Yaz Okulu, Akçakoca, s. 244-262.
• Altunkaynak, Ş., and Yılmaz, Y., 1998. The Mo- unt Kozak magmatic complex, Western Anatolia. Journal of Volcanology and Geothermal Research, 85, 211-231.
• Altunkaynak, Ş., and Dilek, Y., 2006. Timing and nature of postcollisional volca- nism in western Anatolia and geody- namic implications. In: Y. Dilek and S. Pavlides (eds.), Postcollisional Tecto- nics and Magmatism in the Mediterra- nean Region and Asia: Geological Soci- ety of American Special Paper 409, pp. 321-351.
• Altunkaynak, S., Rogers, N. W., and Kelley, S. P., 2010. Causes and effects of geoc- hemical variations in late Cenozoic vol- canism of the Foça volcanic centre, NW Anatolia, Turkey. International Geology Review, 52, 579-607.
• Bacon, C.R., 1986. Magmatic inclusions in si- licic and intermediate volcanic rocks.
• Journal of Geophysical Research, 91, 6091-6112.
• Bacon, C.R., and Metz, J., 1984. Magmatic inc- lusions in rhyolites, contaminated ba- salts, and compositional zonation be- neath the Coso volcanic field, California. Contributions to Mineralogy and Petro- logy, 85, 346-365.
• Barbarin, B., and Didier, J., 1992. Genesis and evolution of mafic microgranular enclaves through various types of in- teraction between coexisting felsic and mafic magmas. Transactions of the Ro- yal Society of Edinburgh Earth Scien- ces, 83, 145-153.
• Bozkurt, E., 2000. Timing of extension on the Büyük Menderes Graben, western Tur- key and its tectonic implications. In:
• Tectonics and Magmatism in Turkey
• and the Surroundings Area, E., Bozkurt,
• J.A., Winchester, J.D.A., Piper, (eds.).
• Special Publications, 173, Geological
• Society of London, pp. 385-403.
• Bozkurt, E., 2001. Neotectonics of Turkey- a synthesis. Geodinamica Acta, 14, 3-30.
• Bozkurt, E., 2003. Origin of NE-trending basins in western Turkey. Geodinamica Acta, 16, 61-81.
• Bozkurt, E., and Park, R.G., 1994. Southern Menderes Massif - an incipient meta- morphic core complex in western Ana- tolia, Turkey. Journal of the Geological Society, 151, 213-216.
• Briot, D., 1990. Magma mixing versus xenocryst assimilation: the genesis of trachyande- sites in Sancy volcano, Massif Central, France. Lithos, 25, 227-241.
• Brown, S.J.A., Barley, M.E., Krapez, B., and Cas, R.A.F., 2002. The Late Archaean Melita Complex, Eastern Goldfields, Western Australia: shallow submarine bimodal volcanism in a rifted arc environment.
• Journal of Volcanology and Geothermal
• Research, 115, 303-327.
• Chen, Y.D., Price, R.C., and White, A.J.R., 1989. Inclusions in three S-type granites from southeastern Australia. Journal of Pe- trology, 30, 1181-1218.
• Conrey, R.M., Sherrod, D.R., Hooper, P.R., and Swanson, D.A., 1997. Diverse primitive magmas in the Cascade arc, northern Oregon and southern Washington. The Canadian Mineralogist, 35, 367-396.
• Cox, K.G., Bell, J.D., and Pankhurst, R.J., 1984.
• The Interpretation of Igneous Rocks. Al
• len and Unwin, London.
• Deniel, C., Aydar, E., and Gourgaud, A., 1998.
• The Hasan Dağı Stratovolcano (Central Anatolia, Turkey): evolution from calc- alkaline to alkaline magmatism in a col- lision zone. Journal of Volcanology and Geothermal Resarch, 87, 275-302.
• Didier, J. and Barbarin, B. (eds.), 1991. Enclaves and Granite Petrology: Developments in Petrology 13, Elsevier, Amsterdam.
• Dilek, Y., and Altunkaynak, Ş., 2007. Cenozoic crustal evolution and mantle dynamics of post-collisional magmatism in wes- tern Anatolia. International Geology Re- view, 49, 431-453.
• Dilek, Y., and Altunkaynak, Ş., 2009. Geochemi- cal and temporal evolution of Cenozo- ic magmatism in western Turkey: mant- le response to collision, slab break-off, and lithospheric tearing in an oroge- nic belt. Geological Society of London Special Publications, 311, 213-233.
• Dilek, Y., Altunkaynak, Ş., and Öner, Z., 2009. Syn-extensional granitoids in the Men- deres core complex and the late Ceno- zoic extensional tectonics of the Aege- an province. U. Ring and B. Wernicke (eds.), Extending a Continent: Architec- ture, Rheology and Heat Budget. Geo- logical Society of London Special Pub- lications, 321, 197-223.
• Dodge, F.C.W., and Kistler, R.W., 1990. Some additional observations on inclusions in the granitic rocks of the Sierra Nevada.
• Journal of Geophysical Research, 95, 17841-17848.
• Dorais, M.J., Whitney, J.A., and Stormer, (Jr.) J.C.,
• Mineralogical constraints on the
• petrogenesis of trachytic inclusions, Car
• penter ridge tuff, Central San Juan Vol
• canic Field, Colorado. Contributions to
• Mineralogy and Petrology, 107, 219-230.
• Eichelberger J.C., 1975. Origin of andesite and dacite: evidence of mixing at Glass Mo- untain in California and at other circum pacific volcanoes, Geological Society of America Bulletin, 86, 1381-1391.
• Eichelberger J.C., 1978. Andesite volcanism and crustal evolution. Nature, 275, 21-27.
• Eichelberger JC., 1980. Vesiculation of mafic magma during replenishment of silicic magma chambers. Nature, 288, 446- 450.
• Eichelberger, J.C., Chertkoff, D.G., Dreher, S.T., and Nye, C.J., 2000. Magmas in collisi- on: rethinking chemical zonation in sili- cic magmas. Geology, 28, 603-606.
• Emre, T., and Sözbilir, H., 1996. Tertiary detach- ment faulting, core complex uplift, and graben evolution in the western Ana- tolia extensional province, Turkey. In: Anonymous (eds.), 30th International Geological Congress, Abstracts, p. 288.
• Ercan, T., Günay, E., Çevikbaş, A., Ateş, M., Küçükayman, A., Can, B. ve Erkan, M.
• Bigadiç çevresinin (Balıkesir) jeo
• lojisi, magmatik kayaçların petrolojisi ve
• kökensel yorumu. Maden Tetkik Arama
• Genel Müdürlüğü Jeoloji Dairesi Rapo
• ru, Ankara (yayımlanmamış).
• Erdoğan, B., 1990. Stratigraphic features and tectonic evolution of the İzmir-Ankara Suture Zone in the region between İz- mir and Seferihisar. Türkiye Petrol Jeo- logları Derneği Bülteni, 2, 1-20.
• Erkül, F., 2010. Tectonic significance of synex- tensional ductile shear zones within the Early Miocene Alaçamdağ granites, northwestern Turkey. Geological Maga
• zine, 147 (4), 611-637.
• Erkül, F., Helvacı, C., and Sözbilir, H., 2005a. Evidence for two episodes of volcanism in the Bigadiç borate basin and tectonic implications for western Turkey. Geolo- gical Journal, 40 (5), 545-570.
• Erkül, F., Helvacı, C., and Sözbilir, H., 2005b. Stratigraphy and geochronology of the Early Miocene volcanic units in the Bi- gadiç borate basin, Western Turkey.
• Turkish Journal of Earth Sciences, 14 (3), 227-253.
• Erkül, F., Helvacı, C., and Sözbilir, H., 2006. Oli- vine basalt and trachyandesite peperi- tes formed at the subsurface/surface in- terface of a semi-arid lake : An examp- le from the Early Miocene Bigadiç ba- sin, western Turkey. Journal of Volca- nology and Geothermal Research, 149 (3-4), 240-262.
• Fan, W.M., Guo, F., Wang, Y. J., Lin, G., and
• Zhang, M. 2001. Post-orogenic bimo
• dal volcanism along the Sulu orogenic
• belt in eastern China. Physics and Che
• mistry of the Earth Part a-Solid Earth
• and Geodesy, 26, 733-746.
• Fytikas, M., Giuliani, O., Innocenti, F., Manetti, P., Mazzuoli, R., Peccerillo, A., and Vil- lari, L., 1979. Neogene volcanism of the northern and central Aegean region. Annales Géologiques des Pays Hellé- niques, 30, 106-129.
• Fytikas, M., Innocenti, F., Manetti, P., Mazzuoli, R., Peccerillo, A. And Villari, L. 1984.
• Tertiary to Quaternary evolution of vol
• canism in the Aegean region. In: J.E.
• Dixon and A.H.F. Robertson (eds.), The
• Geological Evolution of the Eastern
• Mediterranean, Geological Society of
• London Special Publication, 17, 687- 699.
• Genç, Ş.C. 1998. Evolution of the Bayramiç magmatic complex, northwestern Ana- tolia. Journal of Volcanology and Geot- hermal Research, 85 (1-4), 233-249.
• Gourgaud, A., 1991. Comagmatic enclaves in lavas from the Mont-Dore composi- te volcano, Massif Central, France, In:
• J. Didier, and B. Barbarin (eds.), Encla
• ves and Granite Petrology, Elsevier, pp. 221-233.
• Groove, T.L., Donnely-Nolan, J.M., and Housch,
• T., 1997. Magmatic processes that ge
• nerated the rhyolite of Glass Mountain,
• Medicine Lake Volcano, north Califor
• nia. Contributions Mineralogy and Pet
• rology, 127, 205-223.
• Guo, F., Fan, W.M., Wang, Y.J., and Lin, G. 2001. Petrogenesis of the late meso- zoic bimodal volcanic rocks in the so- uthern Da Hinggan Mountains, China. Acta Petrologica Sinica, 17, 161-168.
• Gündoğdu, M.N. 1982. Neojen yaşlı Bigadiç se- dimanter baseninin jeolojik, mineralo- jik ve jeokimyasal incelenmesi, Doktora
• Tezi, Jeoloji Mühendisliği Bölümü, Ha
• cettepe Üniversitesi, Ankara (yayımlan- mamış).
• Gündoğdu, M.N., 1984. Bigadiç gölsel Neojen basenin jeolojisi. Yerbilimleri, 11, 91-104.
• Gündoğdu, M.N., 1985, Bigadiç Gölsel Neojen Baseninde karbonat mineralleri ile si- mektitlerin dağılımı. II. Ulusal Kil Sem- pozyumu, s. 123-140.
• Gündoğdu, M.N., Yalçın, H., Temel, A., and Cla- ner, N., 1996. Geological, mineralogi- cal and geochemical characteristics of
• zeolite deposits associates with bora
• tes in the Bigadiç, Emet and Kırka Neo
• gene lacustrine basins, Western Turkey.
• Mineralium Deposita, 31 (6), 492-513.
• Helvacı, C., 1995, Stratigraphy, mineralogy and genesis of the Bigadiç borate deposits, Western Turkey. Economic Geology, 90, 1237-1260.
• Helvacı, C., and Alonso, R.N., 2000. Borate de- posits of Turkey and Argentina; A sum- mary and geological comparison. Tur- kish Journal of Earth Sciences, 24, 1-27.
• Hibbard, M.J., 1991. Textural anatomy of twelve magma-mixed granitoid systems. In: J. Didier and B. Barbarin (eds.), Enclaves and Granite Petrology. Developments of Petrology, Elsevier, pp. 431-444.
• Hibbard, M.J. 1995. Petrography to Petrogene- sis. Prentice Hall, New York.
• Huppert, H.E., Sparks, R.S.J., and Turner, J.S.,
• Effects of volatiles on mixing in
• calc-alkaline magma systems. Nature, 297, 554-557.
• Irvine, T.N., and Baragar, W.R.A., 1971. A guide to the chemical classification of com- mon volcanic rocks. Canadian Journal of Earth Sciences, 8, 523-548.
• Işık, V., and Tekeli, O., 2001. Late orogenic crustal extension in the northern Men- deres massif (western Turkey): eviden- ce for metamorphic core complex for- mation. International Journal of Earth Sciences, 89 (4), 757-765.
• Işık, V., Tekeli O., and Seyitoğlu, G., 2004. The 40Ar/39Ar age of extensional ductile de- formation and granitoid intrusion in the northern Menderes core complex: imp- lications for the initiation of extensional tectonics in western Turkey. Journal of Asian Earth Sciences, 23, 555-566.
• Kabeto, K., Sawada, Y., Iizumi, S., and Wakatsu- ki, T., 2001. Mantle sources and magma- crust interactions in volcanic rocks from the northern Kenya rift: geochemical evi- dence. Lithos, 56, 111-139.
• Karacık, Z., and Yılmaz, Y., 1998. Geology of the ignimbrites and the associated vol- canoplutonic complex of the Ezine area, northwestern Anatolia. Journal of Vol- canology and Geothermal Research, 85, 251-264.
• Koçyiğit, A., Yusufoğlu, H., and Bozkurt, E.
• Evidence from the Gediz gra
• ben for episodic two-stage extension in
• western Turkey. Journal of the Geologi
• cal Society, London, 156, 605-616.
• Kouchi, A., and Sunagawa, I., 1983. Mixing ba- saltic and dacitic magmas by forced convection. Nature, 304, 527-528.
• Kouchi, A., and Sunagawa, I., 1985. A model for mixing basaltic and dacitic magmas as deduced from experimental data. Cont- ributions to Mineralogy and Petrology, 89, 17-23.
• Koyaguchi, T., 1986. Textural and compositio- nal evidence for magma mixing and its mechanism, Abu volcano group, So- uthwestern Japan. Contributions to Mi- neralogy and Petrology, 93, 33-45.
• Kumar, S., 1995. Microstructural evidence of magma quenching inferred from encla- ves hosted in the Hodrusa Granodiori- tes, Western Carpathians. Carpathian Geology, 46, 379-382.
• Le Maitre, R.W., Bateman, P., Dudek, A., Keller,
• J., Lameyre, J., Le Bas, M.J., Sabine,,
• P.A., Schmid, R., Sorensen, H., Stre
• ickeisen, A., Woolley, A.R., and Zanet
• tin, B., 1989. A Classification of Igneo
• us Rocks and Glossary of Terms. Re
• commendations of the IUGS Subcom
• mission on the Systematics of Igneous
• Rocks, Blackwell Scientific Publication, Trowbridge, Wilts.
• Lindline, J., Crawford, W.A., Crawford, M.L., and Omar, G.I., 2000. Post accretion magmatism within the Kuiu-Etolin igne- ous belt, southeastern Alaska. The Ca- nadian Mineralogist, 38 (4), 951-974.
• Luhr, J.F., and Carmichael, I.S.E., 1980. The Co- lima volcanic complex, Mexico, I. post- caldera andesites from Volcan Colima. Contributions to Mineralogy and Petro- logy, 71, 343-372.
• Moraes, R., Fuck, R.A., Pimental, M.M., Gioia, S., and Figueiredo, A.M.G., 2003. Geo- chemistry and Sm-Nd isotopic charac- teristics of bimodal volcanic rocks of
• Juscelandia, Goias, Brazil: Mesoprot
• erozoic transition from continental rift
• to ocean basin. Precambrian Research, 125, 317-336.
• Ngounouno, I., Deruelle, B., and Demaiffe, D. 2000. Petrology of the bimodal Ceno
• zoic volcanism of the Kapsiki plateau
• (northernmost Cameroon, Central Afri
• ca). Journal of Volcanology and Geot
• hermal Research, 102 (1-2), 21-44.
• Okay A.I., and Siyako M. 1993. The revised lo- cation of the İzmir-Ankara Suture in the region between Balıkesir and İzmir. In:
• Tectonics and Hydrocarbon Potential
• of Anatolia and Surrounding Regions. S.
• Turgut (ed.). pp. 333-355.
• Pe-Piper, G., and Piper, D.J.W., 1989. Spatial and temporal variation in Late Cenozo- ic back-arc volcanic rocks, Aegean Sea Region. Tectonophysics, 169, 113-134.
• Pe-Piper, G. and Piper, D.J.W. 2001. Late Ce- nozoic post-collisional Aegean igneous rocks: Nd and Sr isotopic constraints on petrogenetic and tectonic models. Geological Magazine, 138, 653-668.
• Ring, U., and Collins, A.S., 2005. U-Pb SIMS dating of synkinematic granites: timing of core complex formation in the nort- hern Anatolide belt of western Turkey.
• Journal of the Geological Society, 162, 289-298.
• Sakuyama, M., 1981. Petrological study of the Myoko and Kurohime volcanoes, Ja- pan: crystallization sequence and evi- dence for magma mixing. Igneous Pet- rology, 224, 553-583.
• Seyitoğlu, G., and Scott, B., 1992. Late Ceno- zoic volcanic evolution of the northeas- tern Aegean region. Journal of Volca- nology and Geothermal Research, 54, 157-176.
• Seyitoğlu, G., and Scott, B.C., 1996. The cau- se of N-S extensional tectonics in wes- tern Turkey: Tectonic escape vs back- arc spreading vs orogenic collapse Jo- urnal of Geodynamics, 22, 145-153.
• Seyitoğlu, G., Scott, B., and Rundle, C.C. 1992.
• Timing of Cenozoic extensional tecto
• nics in west Turkey. Geological Society
• of London, 149, 533-538
• Seyitoğlu, G., Anderson, D., Nowell, G., and Scott, B., 1997. The evolution from Mi- ocene potassic to Quaternary sodic magmatism in western Turkey: impli- cations for enrichment processes in the litospheric mantle. Journal of Volca- nology and Geothermal Research, 76, 127-147.
• Seymour, K.S.T., and Vlassopoulos, D., 1992. Magma mixing at Nisyros volcano, as inferred from incompatible trace- element systematic. Journal Volca- nology and Geothermal Research, 50, 273-299.
• Silva, M.M.V.G., Neiva, A.M.R., and Whitehouse, M.J., 2000. Geochemistry of enclaves and host granites from the Nelas area, Central Portugal. Lithos, 50, 153-170.
• Sözbilir, H., 2001. Extensional tectonics and the geometry of related macroscopic struc- tures with their relations to the exten- sional tectonics: Field evidence from the Gediz detachment, western Turkey.
• Turkish Journal of Earth Sciences, 10, 51-67.
• Sözbilir, H., 2002. Revised stratigraphy and fa- cies analysis of Palaeocene-Eocene supra-allochthonous sediments (Deniz- li, SW Turkey) and their tectonic signifi- cance. Turkish Journal of Earth Scien- ces, 11, 87-112.
• Stimac J.A., Pearce T.H., Donnely-Nolan J.M., and Hearn J.R.B.C., 1990. The ori- gin and implications of undercooled andesitic inclusions in rhyolites, Cle- ar Lake volcanics, California. Journal of Geophysical Research, 95, 17729- 17746.
• Sun, S.S., and McDonough, W.F., 1989. Che- mical and isotopic systematics of oce- anic basalts: implication for mantle composition and processes. In: A.D. Saunder and M.J. Norry (eds.), Mag- matism in the Ocean Basins, Geolo- gical Society Special Publication, 42, 313-345.
• Temel, A., 2001. Post-collisional miocene alkali- ne volcanism in the Oğlakçı region, Tur- key: Petrology and geochemistry. Inter- national Geology Review, 43 (7), 640- 660.
• Temel, A., and Gündoğdu, M.N., 1988. Distribu- tion and characteristics of primary se- dimentary structures in borate contai- ning sedimentary units within the Biga- diç lacustrine volcanosedimentary ba- sin of Neogene age, NW Turkey. METU Journal of Pure and Applied Sciences, 21, 251-269.
• Thomson, S.N., and Ring, U., 2006. Thermoch- ronologic evaluation of postcollision ex- tension in the Anatolide orogen, wes- tern Turkey. Tectonics, 25(3) (TC3005, doi: 10.1029/2005TC001833).
• Türkiye Jeoloji Haritası-İzmir, (1:500.000), 1964. Maden Tetkik ve Arama Genel Müdür- lüğü.
• Vernon, R.H., 1983. Restite, xenoliths and mic- rogranitoid enclaves in granites. Clarke Memorial Lecture, Proceedings of the Royal Society, 116, 77-103.
• Wiebe, R.A., 1994. Silicic magma chambers as traps for basaltic magmas: the Cadillac mountain intrusive complex, Mount De- sert island, Maine. Geological Journal, 102, 423-427.
• Wiebe, R.A., and Adams, S.D., 1997. Felsic enc- lave swarms in the Gouldsboro grani- te, Coastal Maine: a record of erup- tion through the roof of a silicic mag- ma chamber. Geological Journal, 105, 617-627.
• Yılmaz, Y., Genç, Ş.C., Gürer, F., Bozcu, M., Yıl- maz, K., Karacık, Z., Altunkaynak, Ş., and Elmas, A., 2000. When did the wes- tern Anatolian grabens begin to deve- lop? E. Bozkurt, J.A. Winchester and J.D.A. Piper (eds.), Tectonics and Mag- matism in Turkey and the Surrounding Area, Geological Society, London, Spe- cial Publications, 173, 353-384.
• Yılmaz, Y., Genç, C., Karacık, Z., and Altunkay- nak, Ş., 2001. Two Contrasting mag- matic associations of NW Anatolia and their tectonic significance. Journal of Geodynamics, 31, 243-271.