Author: Kerim KOÇAK, Gürsel KANSUN
Publishing Date: 2008
ISSN: 2147-9364
Volume: 23 Issue: 1
ABSTRACT:
This study aims to determination of mineralogical and chemical characteristics, and interpretation of chemical zoning of the garnets, that formed in Kırşehir and Alanya massifs (KM and AM) experienced metamorphic history with wide P‐T conditions.
Almandine (alm)‐rich garnet generally developed in Ortaköy and Alanya samples. The garnets grown in pelitic gneisses and paragneissic granites, have compositions of Prb0,37‐0.65 Alm4.12‐4.92 Sps0.26‐1.33 Grs0.12‐0.27, and Prb0,45 ‐0.47 Alm4.75‐4.78 Sps0.56‐0.62 Grs0.2 , repectively while garnets from Alanya samples have relatively higher Ca ( Grs1.19‐1.65 ), and lower Fe2+ (Alm3.79‐4.19 ) and Mn (Sps0.03‐1.4 ) contents. In contrast, igneous garnets contain lower Mg and higher Fe3+ contents than those formed in pelitic rocks: Prb0,12 Alm4.83‐4.92 Sps0.91‐0.92 Grs0.04. Pelitic restites are compositionally different than their hosts, with their higher Prb, and lower Alm and Sps contents.
In the garnets, two types of chemical zonings were mainly distinguished: a) as exemplified by Alanya sample, growth zoning defined by enrichment of core in Mn, and consequently enrichment of rim in Mg and Fe. b) Enrichment of core in Mg, and consequently enrichment of rim in Mn, Ca and Fe2+: As examplified by Ortaköy restites, this zoning is attributed to processes of high‐T crystalline volume diffusion and heterogeneous exchange, net transfer reactions and/or fluid flow. A slight or no chemical zoning have developed in the garnets from Ortaköy gneisses and Ortaköy granite owing to destruction of previous growth zoning by diffusional processes.
Key Words: Garnet; Zoning; Kırşehir massif; Alanya massif; Metamorphism.