Abstract:
The foid bearing syenites within the Yozgat Intrusive Complex (YIC), have coarse crystalline, euhedral, dark-black coloured in hand specimen melanite type garnet. They are mainly crop out in Sivritepe, Gedikhasanlı, Mükremin, Karlı hills and Çağlayan vicinity. Foid bearing syenites generally are in the composition of pyroxene syenite, foid syenite, melanite bearing foid syenite, foid syenite porphyry and pyroxene bearing foid syenite porphyry. The scope of this study, is to use the Raman spectra of melanites of the foid syenites to evaluate their significant behavior in the crystallization process of the unit. Melanites are represent the member of the black andradite type of the garnet group. Melanite, is crystallized from the silica undersaturated magma with the Ca3(Fe3+,Ti)2(SiO4)3 chemical formula. Melanites exhibit clear with high spectrum in Raman spectroscopic determinations due to the silicate structure form and their high symmetrical habit within the crystal systems. The melanites are dark brown in color, euhedral shape, with high optical relief and are isotropic under the polarizing microscope. Raman spectra of melanites are identical with the andradite in composition and generally show Raman shift peaks in the range of 170-1000 cm-1. The melanite has 13 spectra in the total, of the 12 spectra of these spectra are asymmetrical and only one spectra has symmetrical character. Three groups of Raman spectra of the melanitetype are identical with the andradites Raman spectra. These are distributed as 371 cm-1, 522 cm-1 and 879 cm-1 respectively. The Raman spectra of the melanites are obtained in two main regions: (a) external vibration below 400 cm-1 and (b) internal vibration above 400 cm-1. The first part of the external vibration up to 400 cm-1 is related to SiO4 tetrahedra and divalent cations. The internal vibration of these garnets belongs to the SiO4 and their spectra are wavenumber ranges of 400-1050 cm-1. Si-O bending modes are observed in the spectral region between 400 and 600 cm-1, and Si-O stretching modes are observed in the spectral region between 700 and 1050 cm-1. The compositional spectra and vibrational modes of the melanites in the YIC show that the crystallization and differentiation processes have been affected by the interaction of different sources of the components rather than the pure main silica undersaturated magma during their crystallization.
