Origin of phlogopite occurrences related to ultramafic plutonic rocks in the sivas-yıldızeli area

Abstract

The different two series/associations as Upper Cretaceous Karakoç plutonics and Paleocene felsic plutonic rocks belonging to Central Anatolian Plutonics are present in the Yıldızeli area. Karakoç plutonics consist of ultramafic and mafic rocks and are of transition into each other. Phlogopite mineralizations related to Karakoç plutonics are surrounded by Yıldızeli metamorphic rocks and cut by felsic plutonic and vein rocks. Garnet-scapolite-epidote-phlogopitic pyrometasomatic occurrences are seen within the zones intruded by dikes. Packages of phlogopite plates (1-5 cm) are surrounded by a zone (10-15 cm) with pyroxene and/or hornblendes in which garnet, epidote and scapolite layers and/or lenses are found in places. Phyllosilicates are formed of smectite, C-S (chlorite-smectite), chlorite and P-V/I-V (phlogopite-vermiculite/illite-vermiculite) in the Karakoç plutonics, smectite, chlorite and I-S (illite-smectite) in the mafic plutonic rocks, smectite in the felsic plutonic rocks, and 1M Fe-Al phlogopite, smectite, I-V/P-V and S-V (smectite-vermiculite) in the pyrometasomatic rocks. Phlogopite components as Mg/(Mg+Fe) are 0.74 for phlogopite and 0.67 for P-V. Hornblende, scapolite and garnet from the other silicate minerals are Ca-Na-K magnesian hastingsite, mizzonite and grossular in compositions, respectively. Total trace element concentrations decrease phlogopite-P-V-garnet-hornblende-scapolite trend. The distributions of chondrite-normalized trace and rare earth elements (REE) were clearly decreased from garnet-hornblende-scapolite–phlogopite towards P-V and mineral patterns distinguish from each other and also show a clear differentiation/fractionation. ?18O values of phlogopite and P-V have lower than those of mantle and MORB; whereas they are similar to those of continental originated magmatic rocks. ?18O and ?D concentrations of phyllosilicate minerals suggested that the phlogopite and P-V have respectively hypogene and supergene origins. The decreasing ?D and increasing ?18O values indicate phlogopitization trend, whereas those of increasing ?D and decreasing ?18O sign vermiculitization trend. On the other hand, according to granitoid rocks, reflecting initial values for isotopically fractionation, formation temperatures of phlogopite and P-V were obtained as ~ 280 and ~130 °C, respectively that phlogopite and P-V minerals are thought to be pyrometasomatic rather than magmatic origin. In addition, phlogopites are sometimes undergone vermiculite type of negative transformations passing into P-V interphases. © 2016, Hacettepe Universitesi Yerbilmleri. All Rights Reserved.