Akademik Veri Yönetim Sistemi
LITHOS, cilt.246, ss.81-98, 2016 (SCI-Expanded)
Zircon ages, mineral chemistry, whole-rock major and trace element compositions, as well as Sr-Nd isotopic ratios of basaltic (basanite, basalt, and hawaiite with MgO = 3.90-10.06 and SiO2 = 43.18-48.16) to andesitic (SiO2 = 50.86-61.27) and rhyolitic (SiO2 = 71.11-71.13) volcanic rocks (E-W emplaced Nallihan volcanics) in the Lower Eocene terrestrial sedimentary units in the Central Sakarya Zone were studied and compared with those of the northerly located E-W-trending Eocene volcanic rocks (the Kaderbent Volcanics with 52.7-38.1 Ma radiometric ages) that are thought to be related to slab break-off process following the continental collision in the NW Anatolia. Zircon U-Pb ages of the Nallihan volcanics vary from 51.7 +/- 4.7 to 47.8 +/- 2.4 Ma. Clinopyroxene from the basaltic and andesitic rocks record crystallization conditions from similar to 7-8 kbars (similar to 23 km) and similar to 1210 degrees C, to 4.5-1.5 kbars (similar to 14-1.5 km) and 1110-1010 degrees C crystallization conditions, respectively. The olivine-bearing, high-MgO (up to 10 wt%) basaltic rocks of the Nallihan volcanics have nepheline-normative and Na-alkaline compositions, while the andesitic to rhyolitic rocks show calc-alkaline affinity with mainly sodic character. This is the first time this type of volcanic rock has been described in this region. The initial Sr isotopic ratios of both basaltic and andesitic-rhyolitic samples from the Nallihan volcanics are similar (similar to 0.7040-0.7045), indicating that fractional crystallization processes were not accompanied by crustal contamination and that the magma chambers were likely stored within ophiolitic units. Trace element ratios suggest that the Nallihan volcanics were derived from E-MORB- or OIB-like enriched mantle sources, while the Kaderbent volcanics had N-MORB-like depleted mantle sources. Both volcanic units were produced by partial melting of spinet-bearing (shallow) mantle sources that had undergone subduction-related enrichment processes, with the degree of enrichment having been greater for the Kizderbent volcanics.