Geochemistry and origin of plagiogranites from the Eldivan Ophiolite, Çankırı (Central Anatolia, Turkey)

Abstract

Abstract:The Eldivan Ophiolite, exposed around Ankara and Çanklrl cities, is located at the central part of the I · zmirAnkara-Erzincan Suture Zone (IAESZ). It represents fragments of the Neotethyan Oceanic Lithosphere emplaced towards the south over the Gondwanian continent during the Albian time. It forms nearly complete series by including tectonites (harzburgites and rare dunites), cumulates (dunites, wherlites, pyroxenites, gabbro and plagiogranites) and sheeted dykes from bottom to top. Imbricated slices of volcanic-sedimentary series and discontinuous tectonic slices of ophiolitic metamorphic rocks are located at the base of tectonites. Plagiogranitic rocks of the Eldivan Ophiolite are mainly exposed at upper levels of cumulates. They are in the form of conformable layers within layered diorites and also dikes with variable thicknesses. Plagiogranites have granular texture and are mainly composed of quartz and plagioclases. The occurrences of chlorite and epidote revealed that these rocks underwent a low grade metamorphism. Eldivan plagiogranites have high SiO 2 content (70-75 %) and low K 2 O content (0.5-1 %) and display flat patterns of REE with variable negative Eu anomalies. LREE/HREE ratio of these rocks varies between 0.2-0.99. All members of the Eldivan rocks have high LILE/HFSE ratios with depletion of Nb, Ti and P similar to subduction related tectonic settings. Geochemical modelling indicates that the Eldivan plagiogranites could have been generated by 50-90 % fractional crystallization and/or 5-25 % partial melting of a hydrous basaltic magma.

Subduction initiation and back-arc opening north of Neo-Tethys: Evidence from the Late Cretaceous Torbat-e-Heydarieh ophiolite of NE Iran

“…These geochemical features are similar to Sabzevar plagiogranites (Moghadam et al, 2014a) and felsic igneous rocks of convergent plate margins (Pearce et al, 1984). These geochemical signatures are also similar to the geochemical characteristics of plagiogranites from other Tethyan ophiolites of the eastern Mediterranean realm (e.g., (Anenburg et al, 2015;Bonev and Stampfli, 2009;Dilek and Thy, 2006;Osozawa et al, 2012;Uner et al, 2014).…”

Major Late Cretaceous Mass Flows in Central Turkey Recording the Disruption of the Mesozoic Continental Margin

“…The ophiolitic mélange consists of basalt, radiolarian chert, serpentinite, and limestone, with lesser amounts of gabbro, diabase, shale, and sandstone (Çapan & Buket, ; Dangerfield et al, ; Rojay, ; Sarifakioglu et al, ; Tankut et al, ). It includes semiintact ophiolite bodies (Üner et al, ; Uysal et al, ) with Jurassic ages (Çelik et al, ; Dilek & Thy, ). The cherts in the ophiolitic mélanges have yielded Triassic, Jurassic, and Lower Cretaceous radiolarian ages (Sarifakioğlu et al, 2014; Bortolotti et al, ), and some of the pelagic limestones associated with pillow lavas are Lower Cretaceous (Barremian; Rojay et al, ).…”

The Ankara Mélange: an indicator of Tethyan evolution of Anatolia

“…The volcanic-sedimentary unit outcrops largely under the peridotite tectonites (Akyürek 1981;Üner 2010;Üner & Çakır 2011;Üner et al 2014). It is composed of thin layered sedimentary rocks such as red coloured radiolarian cherts, red or green coloured shales, pelagic limestones and alkali basalts.…”