Zafer Aslan

PETROGRAPHY AND PETROLOGY OF THE YÜREKLİ (BALIKESIR) VOLCANICS: AN EXAMPLE OF POST-COLLISIONAL FELSIC VOLCANISM IN THE BIGA PENINSULA (NW TURKEY)

Bu calismada Yurekli volkanitinin (Biga Yarimadasi, KB Turkiye) petrografisi, jeokimyasi ve kokeninin ortaya konulmasi amaclanmistir. Tersiyer volkanizmasinin yaygin oldugu Bati Anadolu (KB Turkiye), tektonik ve magmatik olaylarin berbaber gozlendigi onemli bir kusaktir. Yurekli volkaniti dasitik lav ve piroklastitlerinden olusmaktadir. Dasitik lavlar, porfirik ve hyaloporfirik dokuda olup, ana mineral olarak plajiyoklas, kuvars, amfibol, biyotit, sanidin ve Fe-Ti oksit, tali mineral olarak da apatit ve zirkon icermektedir. Petrolojik acidan, yuksek potasyumlu ve kalk-alkali karakterlidir. N-MORB’a gore normalize iz element diyagraminda buyuk iyon yaricapli litofil element (BIYE) icerikleri yonunde zenginlesme, yuksek cekim alanli element (YCAE) icerikleri bakimindan ise fakirlesme gostermektedir. Kondrite gore normalize edilmis nadir toprak element (NTE) diyagraminda; hafif nadir toprak elementler zenginlesmis, agir nadir toprak elementler ise daha az zenginlesmistir. Ayrica nadir toprak element dagilim sekli konkav (ortalam LaN/LuN=16–25) olup, zayif negatif Eu anomalisi (0.66–0.81) gosterir. Incelenen volkanitlerin gelisiminde plajiyoklas, amfibol ve biyotit fraksiyonel kristallenmesi ve kabuk asimilasyonu rol oynamistir. Elde edilen tum verilere gore, Yurekli volkanitinin carpisma sonrasi ortamda olustugu ve ana magma kaynaginin zenginlesmis litosferik manto ile iliskili oldugu soylenebilir.

SHRIMP U–Pb zircon ages and whole-rock geochemistry for the Şapçı volcanic rocks, Biga Peninsula, Northwest Turkey: implications for pre-eruption crystallization conditions and source characteristics

ABSTRACT Palaeogene and Neogene volcanic rocks are widespread on the Biga Peninsula of Northwest Turkey. These rocks were formed during the Eocene, Oligocene–Miocene, and late Miocene, and the early Miocene Şapçı volcanic rocks in the Balıkesir area consist of andesitic lava flows and associated pyroclastics. Temperatures, pressures, and oxygen fugacities calculated for the hornblendes in these andesitic rocks are 903–930°C, 3.3–4.8 kbar, and –9.91 to –11.88, respectively, and for the biotites they are 755–788°C, 1.30–1.74 kbar, and –14.88 to –13.98, respectively. SHRIMP U–Pb dating of zircons from three andesite samples gave ages of 22.72 ± 0.19, 22.97 ± 0.23, and 18.72 ± 0.17 Ma (early Miocene), and these are regarded as crystallization ages. Geochemical analyses show that the volcanic rocks are mainly high-K and calc-alkaline, and have high contents of large-ion lithophile elements and low contents of high-field strength elements, revealing that they evolved from parental magmas that were derived from an enriched subcontinental lithospheric mantle source. The chondrite-normalized rare earth element patterns of the rocks are concave upwards with LaCN/LuCN = 11.9–21.2 and EuCN/Eu* = 0.84–0.92, implying significant fractional crystallization of hornblende during their evolution. According to the petrological data with regional geology, Neogene magmatic activity on the Biga Peninsula has a post-collisional feature, and was closely related to slab break-off geodynamic model after collision of Tauride–Anatolide Block and Sakarya continent.