Mineralogical, geochemical and thermobarometrical aspects of volcanic rocks in the Central Anatolia
Küçük Resim Yok
Tarih
2011
Yazarlar
Dergi Başlığı
Dergi ISSN
Cilt Başlığı
Yayıncı
Nova Science Publishers, Inc.
Erişim Hakkı
info:eu-repo/semantics/closedAccess
Özet
This chapter focuses on the tectonic and geological settings, analytical methods, petrographical characteristics, geochemical features, mineralogy and mineral chemistry, crystallization conditions, and magmatic processes (mixing, evolution, etc.) of the Neo-Quaternary calc-alkaline and alkaline rocks in Nigde Volcanic Province from Central Anatolia, Turkey. First, in this regard, tectonic and geological settings of the Neo-Quaternary calc-alkaline and alkaline volcanic rocks have been generally presented after the introduction section. Then, analytical methods used for the studied volcanics have been briefly given. Second, the petrographical characteristics and phenocryst assemblages of the calc-alkaline and alkaline volcanic rock types are presented. In such a way that, the Nigde Volcanic Province consists of several stratovolcanoes and monogenetic cones activated in Neogene and Quaternary times. The Neo-Quaternary volcanic rocks are generally andesitic in composition and are characterized by their high phenocryst contents. They show porphyritic, glomeroporphyric and seriate texture and contain wide variety of phenocrysts consisting of plagioclase, orthopyroxene, clinopyroxene, amphibole, biotite. However, the Quaternary volcanic rocks related to the monogenetic cones are alkaline basalts with microlitic-porphyritic texture, and they have lower phenocrysts contents of olivine and clinopyroxene and lesser Ca-rich plagioclase. Third, geochemical features and classifications of the calc-alkaline and alkaline volcanic rocks have been determined. In such a way that, the SiO2 contents of the calc-alkaline rocks change from 55 to 65 wt%, called as basaltic andesite-andesite, and they define medium to high-K calc-alkaline affinities. Their MgO and TiO2 contents are generally lower than 4 and 1 wt%, respectively. The calc-alkaline volcanics show enrichment of LIL elements such as K, Rb, Th and U, depletion in HFSE with negative Nb, Ta, P and Ti anomalies, suggesting an enriched lithospheric mantle source metazomatized by a subduction-related process. On the other hand, the Quaternary volcanic rocks are alkaline in character. Compared to the Neo-Quaternary calc-alkaline andesites, they have lower SiO2 (49-51 wt %), and K2O (0.5-1.7 wt %), and higher MgO (5.1-7.2 wt %) and TiO2 (> 1 % wt) contents, and are classified as basalt. Fourth, mineral chemical features and crystallization conditions of these rock types have been determined and estimated, respectively. As follows, the crystallization conditions range from approximately 750 to 1100 oC and 2.5-8.0 kbars for the calc-alkaline andesitic magma, 885 to 944 oC and 2.0-7.5 kbars for alkaline basaltic magma, which correspond to a depth of 6-24 km for storage region of the Central Anatolian crust. Finally, the magmatic processes (mixing, evolution, etc.) of the calc-alkaline and alkaline volcanic rocks have been discussed. As follows, disequilibrium textures, geochemical characteristics and the compositional variations of the phenocrysts indicate that the calc-alkaline Neo-Quaternary volcanites have a complex evolutionary history. However, mineralogical and geochemical data from the Quaternary alkaline volcanic rocks show a relatively simple evolutionary history. © 2010 by Nova Science Publishers, Inc. All rights reserved.
Açıklama
Anahtar Kelimeler
Alkaline rocks, Calc-alkaline rocks, Crystallization conditions, Geochemistry, Magma mixing, Mineralogy, Volcanites
Kaynak
Rock Chemistry
WoS Q Değeri
Scopus Q Değeri
N/A
