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- MakaleAçık Erişim2017Scopus SJRQ1Evolution of K-rich magmas derived from a net veined lithospheric mantle in an ongoing extensional setting: Geochronology and geochemistry of Eocene and Miocene volcanic rocks from Eastern Pontides (Turkey)
Yücel, Cem; Arslan, Mehmet; Temizel, İrfan; Abdioğlu Yazar, Emel; Ruffet, Gilles
The Eocene and Miocene volcanic rocks between the cities of Trabzon and Giresun in the Eastern Pontides (NE Turkey) erupted as mildly and moderately alkaline magmas ranging from silica-saturated to silica-undersaturated types. 40Ar-39Ar dating and petrochemical data reveal that the studied volcanic rocks are discriminated in two: Lutetian (Middle Eocene) mildly alkaline, (basaltic rocks: 45.31 ± 0.18 to 43.86 ± 0.19 Ma; trachytic rocks: 44.87 ± 0.22 to 41.32 ± 0.12 Ma), and Messinian (Late Miocene) moderately alkaline volcanic rocks (tephrytic rocks: 6.05 ± 0.06 and 5.65 ± 0.06 Ma). The trace and the rare earth element systematic, characterised by moderate light earth element (LREE)/heavy rare earth element (HREE) ratios in the Eocene basaltic and trachytic rocks, high LREE/HREE ratios in the Miocene tephrytic rocks, and different degrees of depletion in Nb, Ta, Ti coupled with high Th/Yb ratios, show that the parental magmas of the volcanic rocks were derived from mantle sources previously enriched by slab-derived fluids and subducted sediments. The Sr, Nd and Pb isotopic composition of the Eocene and Miocene volcanic rocks support the presence of subduction-modified subcontinental lithospheric mantle. During the magma ascent in the crust, parental magmas of both the Eocene and Miocene volcanic rocks were mostly affected by fractional crystallisation rather than assimilation coupled with fractional crystallisation and mixing. The silica-undersaturated character of the Miocene tephrytic rocks could be attributed to assimilation of carbonate rocks within shallow-level magma chambers. The parental magmas of the Eocene volcanic rocks resulted from a relatively high melting degree of a net veined mantle and surrounding peridotites in the spinel stability field due to an increase in temperature, resulting from asthenospheric upwelling related to the extension of lithosphere subsequent to delamination. The parental magmas for the Miocene volcanic rocks resulted from a relatively low melting degree of a net veined mantle domain previously modified by metasomatic melts derived from a garnet peridotite source after decompression due to extensional tectonics, combined with strike-slip movement at a regional scale related to ongoing delamination.
AtıfScopus77WoS74OpenAlex86
İncele - MakaleYalnız künye2014Scopus SJRQ4Origin of analcimes in the Tertiary volcanic rocks from the Eastern Pontides (NE Turkey): A textural, mineralogical and geochemical approach
Yücel, Cem; Temizel, Irfan; Abdioʇlu, Emel; Arslan, Mehmet; Yaʇcioʇlu, Ufuk Celal
Silica-undersaturated mafic volcanic rocks of Tertiary age in form of lava flows, dikes and sills of tephritic compositions extend along the northern part of the Eastern Pontides. These rocks typically contain Ca-clinopyroxene (Wo32-53En26-54Fs8-24), analcime, Fe-Ti oxides, apatite and minor olivine, plagioclase (An49 - 94), K-feldspar (Or29 - 66), hornblende and phlogopite in microgranular porphyritic, hyalo-microlitic porphyritic and glomeroporphyritic textures. Petrochemical features of the studied rocks, such as enrichment in LILE, depletion in Nb, Ta and Ti and moderate or high LREE/HREE ratios, provide strong evidence for melt production from a subduction-metasomatized lithospheric mantle. Besides, the rocks are characterized by their low K2O contents and low K2O/Na2O ratios as a result of analcimization. Analcime detected in these rocks appears to have formed by pseudomorphic mineral replacement reactions. Euhedral or anhedral analcime crystals, 100 - 600 um in diameter, are set in groundmass and display six-sided polygon or rounded shape and irregular cracks. The analcime pseudomorphs are colourless, milky white to grey and occur in clinopyroxene or in the groundmass. Based on the electron microprobe results, analcimes contain a minor amount of cations other than Na and probably represent the remnants of leucite as marked by K-zoning. X-ray diffraction studies of the analcime-bearing samples confirm the presence of cubic and tetragonal analcime crystals in addition to tetragonal leucite. The presence of Ca-clinopyroxene and plagioclase rather than their sodic equivalents, presence of anhydrous mineral phases and lack of Na differentiation trend as well as partial alteration of the rocks likely supports the secondary growth of analcime either during cooling or after magma solidification.
AtıfScopus16WoS17OpenAlex17İncele