Determination of the origin and geothermobarometric properties of rocks belonging to the metamorphic sole at the base of Örencik ophiolite (Burdur-Acıgöl)

The study area, which is located within the Lycian Nappes, one of the Western Anatolian Tectonic Units, consists of Jurassic-Upper Cretaceous aged Örencik Ophiolite, Upper Cretaceous aged Kızılcadağ Ophiolitic Melange, Cenomanian-Turonian aged Iğdir Metamorphites and Quaternary aged alluvium. In this study, the origin of the rocks belonging to the metamorphic sole at the base of the ophiolite the mineralogy, petrography, geochemical properties and the factors (heat, pressure, type of subduction, etc.), that are effective in the metamorphic process are explained by evaluating together. Igdir Metamorphites consist of garnet amphibolite, amphibolite, amphiboleschist and micaschist. The mineralogical compositions of these rocks are generally amphibole, plagioclase, garnet, clinopyroxene, quartz, muscovite, biotite, epidote, chlorite, magnetite and sphene. According to the petrographic findings, the amphibolites contain different mineral assemblages that define metamorphism from the low temperature zone of the greenschist facies to the upper amphibolite-granulite facies transition. Geochemical studies of the Igdir Metamorphites amphibolites indicate that the amphibolites are composed of two different mafic igneous rocks with alkaline and tholeiitic character belonging to the oceanic crust. Thermobarometric results show that the origin rocks of Igdir Metamorphites underwent metamorphism at depths of about 8 km - 30 km, temperatures between 440 ºC - 700 ºC and pressures between 2 kbar-10 kbar on the subducting oceanic lithosphere slice. Inverted metamorphism developed in the amphibolites of Igdir Metamorphites with a thickness of approximately 300 m. The degree of metamorphism decreases from bottom to top. In the lower part, high temperature mineral parageneses representing the upper amphibolite-granulite transition facies are located at the contact with mantle peridotites, while in the upper parts, low temperature metamorphic mineral parageneses representing the low temperature zone of the greenschist facies occur at the contact with the Kızılcadağ Ophiolite Melange. According to the mineral chemistry results, the amphiboles of Igdir Metamorphites are in the calcic amphibole class. Amphiboles represent chermakite, magnesio-hornblende, edenite, pargazite, and sadanagite type amphiboles. One sample was identified as cummingtonite from Mg-Fe-Mn type amphiboles. As the degree of metamorphism increases, Mg, Fe and Si values decrease while Al and Na values increase in amphiboles. When the geological, petrographic, petrological, thermobarometric and mineral chemistry results are evaluated together; the original rocks of the İğdir metamorphite are in the intraoceanic subduction zone within the İzmir-Ankara Neotethys ocean, mafic igneous rocks of alkaline and tholeitic character on the subducting oceanic slice, at depths of 8 km-30 km, between 440 ºC-700 ºC in temperatures and between 2 kbar-10 kbar in pressures show that it has undergone metamorphism and amphibolitized during the Cenomanian-Turonian time.