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- Derleme MakaleYalnız künye2014Mineral chemistry and thermobarometry of Eocene monzogabbroic stocks from the Bafra (Samsun) area in Turkey: Implications for disequilibrium crystallization and emplacement conditions
Temizel, İrfan; Arslan, Mehmet; Abdioğlu, Emel; Yücel, Cem
Monzogabbro stocks including felsic enclaves (monzosyenite) around the Bafra (Samsun) area at the western edge of the Eastern Pontides cut Eocene-aged volcanic and sedimentary units. The monzogabbros contain plagioclase, alkali feldspar, clinopyroxene, olivine, hornblende, biotite, apatite, and iron-titanium oxides, whereas the felsic enclaves contain alkali feldspar, plagioclase, hornblende, biotite, clinopyroxene, and iron-titanium oxides. Mineral chemistry data suggest that magmas experienced hydrous and anhydrous crystallization in deep and shallow crustal magma chambers. Several thermobarometers were used to estimate temperatures of crystallization and emplacement for the mafic and felsic magmas. Clinopyroxene thermobarometry yielded 1100-1232 C and 5.9-8.1 kbar for monzogabbros, and 931-1109 C and 1.8-6.9 kbar for felsic enclaves. Hornblende thermobarometry and oxygen fugacity estimates reveal 739-971°C, 7.0-9.2 kbar and 10−9.71 for monzogabbros and 681-928°C, 3.0-6.1 kbar and 10−11.34 for felsic enclaves. Biotite thermobarometry shows elevated oxygen fugacity varying from 10−18.9-10−11.07 at 632-904°C and 1.29-1.89 kbar for monzogabbros, to 10−15.99 -10−11.82 at 719-873°C and 1.41-1.77 kbar for felsic enclaves. The estimated zircon and apatite saturation temperatures are 504-590°C and 693-730°C for monzogabbros and 765-775°C and 641-690°C for felsic enclaves, respectively. These data imply that several phases in the gabbroic and syenitic magmas did not necessarily crystallize simultaneously and further indicate that the mineral compositions may register intervals of disequilibrium crystallization. Besides, thermobarometry contrasts between monzogabbro and felsic enclave may be partly a consequence of extended interactions between the mafic and felsic magmas by mixing/mingling and diffusion. Additionally, the hot felsic magma was close to liquidus conditions (crystallinity < 30%) when injected into cooler mafic magma (crystallinity > 50%), and thus, the monzogabbro stocks reflect hybrid products from the mingling and incomplete mixing of these two magmas.
- MakaleYalnız künye2008Magma interaction processes inferred from Fe-Ti oxide compositions in the Dölek and Sariçiçek plutons, Eastern Turkey
Karsli, Orhan; Aydin, Faruk; Uysal, Ibrahim; Sadiklar, M. Burhan
Magnetite-ulvöspinel and ilmenite-hematite solid solution intergrowths from the high-K calc-alkaline Dölek and Sarιçiçek plutons, Eastern Turkey, were investigated using microprobe analyses. Compositions of twenty-eight samples from the host rocks and their enclaves' in the plutons were used to estimate the oxygen fugacity and temperature. The ilmenite and ulvöspinel component exsolves out along certain preferred crystallographic planes in the titanomagnetite of the host rocks, while they are always absent in those of the mafic-microgranular enclaves. The titanomagnetite and ilmenite show variations as Mt98-70Usp02-30 and Ilm99-65Hm01-35 in composition, respectively. Estimations of oxygen fugacity and temperature using the titanomagnetite-ilmenite thermometry/oxygen barometry range from log/O2 of -15.30 to -20.48 in host rocks, log/O2 of -15.39 to -20.80 in the mafic microgranular enclaves and 617±6 to 758±23 °C in host rocks, 622±6 to 735±24 °C in the mafic microgranular enclaves, possibly indicating crystallisation temperature. Applying magnetite-ilmenite thermometry/ oxygen barometry to the granitoid rocks also involves microprobe analyses of ilmenite lamellae in titanomagnetite and this method yielded mean temperatures of 679±18 °C. The specific forms and chemical properties of Fe-Ti oxides, and similarities in crystallization temperature and oxygen fugacity of the host rocks and the mafic microgranular enclaves (MME) obtained from the Fe-Ti oxide pairs imply that thermal equilibrium probably occurred between two contrasted magmas, which mixed invarious proportion so that possibly a felsic and a more mafic magma interaction occurred in a convectively dynamic magma chamber during crystallization of the plutons. Probably, underplating may be responsible for genesis of the hybrid plutons. Thus, for mixing of coeval magmas derived from a lithospheric upper mantle (mafic end-member) and lower crust (felsic end-member), a thermal anomaly should be supplied. Upwelling of hot asthenospheric material result in thermal perturbation and melting of lithospheric mantle. Intrusion of hot lithospheric mantle-derived mafic magma then induced lower crustal melting, producing felsic melt. Mixing of the lower crust-derived melt and lithospheric mantle-derived magma formed the hybrid pluton. This process requires a post-collisional extensional tectonic setting during the Eocene in the Eastern Pontides.
- MakaleYalnız künye2007Geochemical and Sr-Nd-Pb isotopic compositions of the Eocene Dölek and Sariçiçek Plutons, Eastern Turkey: Implications for magma interaction in the genesis of high-K calc-alkaline granitoids in a post-collision extensional setting
Karsli, Orhan; Chen, Bin; Aydin, Faruk; Şen, Cüneyt
The major and trace elements and Sr-Nd-Pb isotopes of the host rocks and the mafic microgranular enclaves (MME) gathered from the Dölek and Sariçiçek plutons, Eastern Turkey, were studied to understand the underlying petrogenesis and geodynamic setting. The plutons were emplaced at ∼ 43 Ma at shallow depths (∼ 5 to 9 km) as estimated from Al-in hornblende geobarometry. The host rocks consist of a variety of rock types ranging from diorite to granite (SiO2 = 56.98-72.67 wt.%; Mg# = 36.8-50.0) populated by MMEs of gabbroic diorite to monzodiorite in composition (SiO2 = 53.21-60.94 wt.%; Mg# = 44.4-53.5). All the rocks show a high-K calc-alkaline differentiation trend. Chondrite-normalized REE patterns are moderately fractionated and relatively flat [(La/Yb)N = 5.11 to 8.51]. They display small negative Eu anomalies (Eu/Eu* = 0.62 to 0.88), with enrichment of LILE and depletion of HFSE. Initial Nd-Sr isotopic compositions for the host rocks are εNd(43 Ma) = - 0.6 to 0.8 and mostly ISr = 0.70482-0.70548. The Nd model ages (TDM) vary from 0.84 to 0.99 Ga. The Pb isotopic ratios are (206Pb/204Pb) = 18.60-18.65, (207Pb/204Pb) = 15.61-15.66 and (208Pb/204Pb) = 38.69-38.85. Compared with the host rocks, the MMEs are relatively homogeneous in isotopic composition, with ISr ranging from 0.70485 to 0.70517, εNd(43 Ma) - 0.1 to 0.8 and with Pb isotopic ratios of (206Pb/204Pb) = 18.58-18.64, (207Pb/204Pb) = 15.60-15.66 and (208Pb/204Pb) = 38.64-38.77. The MMEs have TDM ranging from 0.86 to 1.36 Ga. The geochemical and isotopic similarities between the MMEs and their host rocks indicate that the enclaves are of mixed origin and are most probably formed by the interaction between the lower crust- and mantle-derived magmas. All the geochemical data, in conjunction with the geodynamic evidence, suggest that a basic magma derived from an enriched subcontinental lithospheric mantle, probably triggered by the upwelling of the asthenophere, and interacted with a crustal melt that originated from the dehydration melting of the mafic lower crust at deep crustal levels. Modeling based on the Sr-Nd isotope data indicates that ∼ 77-83% of the subcontinental lithospheric mantle involved in the genesis. Consequently, the interaction process played an important role in the genesis of the hybrid granitoid bodies, which subsequently underwent a fractional crystallization process along with minor amounts of crustal assimilation, en route to the upper crustal levels generating a wide variety of rock types ranging from diorite to granite in an extensional regime.