Petrography, petrochemistry,U-Pb zircon geochronology, whole-rock Sr-Nd-Pb and zircon Lu-Hf isotope geochemistry and petrogenesis of the eocene Kazıkbeli pluton (Kürtün-Gümüşhane)

In this study, the Kazıkbeli Pluton located to the Kürtün (Gümüşhane) area in the northern part of the Eastern Pontides were investigated by using petrography, mineral chemistry, zircon U-Pb geochronology, whole-rock and Sr-Nd-Pb isotope geochemistry and zircon Lu-Hf isotope geochemistry data. The Kazıkbeli Pluton extend NE-SW directions and spreads approximately in an area of 44 km2. The compositions of the rocks vary from gabbroic diorite to granite, and they are mainly composed of plagioclase (An25-65), orthoclase (Or1-3), quartz, amphibole (Mg#=0.63-0.73), biotite (Mg#=0.52-0.58) and Fe-Ti oxides. The crystallization ages are 46.06 ± 0.24 Ma for gabbroic diorites and 45.55 ± 0.26 Ma for granodiorites, corresponding to the Lutetian (middle Eocene) period. The Kazıkbeli Plüton are I-type, high-K calc-alkaline and mostly metaluminous and less pealuminous in character. Major and trace element variations show plagioclase, amphibole and Fe-Ti oxide fractionations which are effective in rocks evolution. εNd(i) values of the rocks range from 1.85 to 2.24, whereas 87Sr/86Sr(i) values range from 0.70458 to 0.70484. 206Pb/204Pb(i), 207Pb/204Pb(i), and 208Pb/204Pb(i) contents change from 18.50 to 18.57, 15.60 to 15.61 and 38.56 to 38.59, respectively. εHf(i) values range from 5.75 to 8.03. All data indicate that the studied plutonic rocks were derived by partial melting of the lithospheric mantle, with relatively minor contribution from the crustal rocks. The crystallization temperatures (706-828 °C), pressures (0.6-0.9 kbar) and oxygen fugacity (ƒO2=-12.5 to -13.8) of the studied rocks during crystallization are mostly similar. These data indicate that the studied plutonic rocks were emplaced in a relatively shallow depth.