Petrology of the Kurancali phlogopitic metagabbro: An island arc-type ophiolitic sliver in the Central Anatolian Crystalline Complex

The Kurancali metagabbro occurs as an isolated body in the central part of the Central Anatolian Crystalline Complex. It has been emplaced along a ste ep S-vergent thrust-plane onto the uppermost units of the Central Anatolian Metamorphics. The main body of the Kurancali metagabbro is characterized b y distinct compositional layering. The layered gabbros comprise pyroxene an d hornblende gabbros. Phlogopite-rich, plagioclase-hornblende gabbro occurs mainly as pegmatitic dikes intruding the layered gabbro sequence. The laye red gabbros, in general, consist mainly of diopsidic augites, brown hornble ndes, and plagioclase. Secondary phases are phlogopitic mica, brownish-gree n hornblende replacing clinopyroxenes, and fibrous, greenish actinolitic ho rnblende partially or completely replacing brown homblende. The primary dar k micas are phlogopitic in the range of phlogopite((57-70)) and annite((30- 43)). The analyzed pyroxenes are diopsidic (En(32)Fs(19)Wo(49)En(35)Fs(18)W o(48)). The whole-rock geochemistry of the gabbros indicates the presence of two di stinct groups of rocks; a less pronounced group of phlogopite gabbro with i sland-are calc-alkaline affinities. and a dominating layered gabbro sequenc e with island-arc tholeiite characteristics. They are extremely enriched in LILE, indicative of alkaline metasomatism in the source region, and displa y geochemical features of transitional backarc-basin basalts (BABB)/island- arc basalts (IAB)-and IAB-type oceanic crust. Based on their geochemical si milarities to modem island-arc basements, we suggest that the Kurancali met agabbro may represent the basement of an initial island arc, generated in a supra-subduction zone setting within the Izmir-Ankara branch of Neotethys.