Journals / Turkish Journal of Earth Sciences / 2007 / Cilt: 16 - Sayı: 2
Stratigraphy and Geochemical Features of the Early Miocene Bimodal (Ultrapotassic and Calc-alkaline) Volcanic Activity Within the NE-trending Selendi Basin, Western Anatolia, Turkey
- Pages
- 117–139
- DOI
- —
Abstract
Western Anatolia has experienced thickening and orogenic collapse subsequent to the Eocene continent-arc collision. The early stage of the post-collisional volcanism in the region was thought to have produced widespread lavas and pyroclastic deposits of calc-alkaline basaltic andesite to rhyolite composition. However, in the Selendi Basin, one of the NE-trending basins in western Anatolia, there are two distinct volcanic unit compositions associated with the Lower Miocene sedimentary rocks: (1) a calc-alkaline, high-potassic felsic unit; and (2) alkaline, ultrapotassic lamproitic units, i.e. both are bimodal in character. The calc-alkaline felsic volcanic rocks (Eğreltidağ volcanic unit) are composed of wide-spread pyroclastic rocks and lava flows, whilst the ultrapotassic-lamproitic mafic rocks (Kuzayır lamproite) consist of small-volume syn-sedimentary lava flows. The geochemical characteristics of the Kuzayır lamproite are similar to those of the ´Mediterranean lamproites` that were widely produced in post-orogenic tectonic settings. A temporal and spatial association between these volcanic units clearly describes a post orogenic bimodal volcanic activity. The data also imply that the continental extensional tectonic regime in western Anatolia began, at least, in the Early Miocene, and produced not only calc-alkaline felsic activity but also mantle-derived alkaline, ultrapotassic volcanic rocks.
Özet
Bat› Anadolu, Eosen’deki k›ta-yay çarp›flmas›ndan sonra kabuksal kal›nlaflma ve orojenik çökme olaylar› ile flekillenmifltir. Bölgede, çarp›flma sonras› volkanizman›n ilk evresinin (Erken Miyosen), bazaltik andezitten riyolite kadar de¤iflen bileflimlerde kalk-alkali volkanik ürünler verdi¤i kabul edilir. Bat› Anadolu’da kuzeydo¤u uzan›ml› havzalardan birisi olan Selendi Havzas›nda ise, iki farkl› bileflimli volkanik birim Erken Miyosen yafll› tortul kayaçlar ile giriklilik sunar. Bunlar, (1) kalk-alkali yüksek-K’lu felsik ve (2) alkali, ultrapotasik lamproitik birimler olup bileflim bak›m›ndan bimodal karakterlidirler. Kalk-alkali felsik volkanik kayaçlar (E¤reltida¤ volkanik birimi) genifl yay›l›ml› piroklastik kayaçlar ve lavlardan; ultrapotasik-lamproitik mafik kayaçlar ise (Kuzay›r lamproiti) az miktarda, tortullaflmayla yafl›t lav akmalar›ndan oluflur. Kuzay›r lamproitinin jeokimyasal özellikleri ‘Akdeniz lamproitleri’ olarak da an›lan ve da¤oluflum sonras› tektonik ortamlarda geliflen lamproitlere benzerlik sunar. Di¤er çarp›flma ortamlar›nda da oldu¤u gibi, bu iki volkanik birimin zamansal ve konumsal birlikteli¤i da¤oluflum sonras› bimodal volkanik aktiviteyi tan›mlamaktad›r. Ayr›ca, bu veriler Bat› Anadolu’da genifllemeli tektonik rejimin en az›ndan Erken Miyosen’de bafllam›fl oldu¤unu ve yaln›zca kalk-alkali felsik bileflimli volkanik aktiviteyi de¤il, bunun yan› s›ra, mantodan türeme alkali ve ultrapotasik bileflimli volkanikleri de üretti¤ini ifade eder.