Clays and Clay Minerals, Vol. 56, No. 2, 207–221, 2008.
Loading...
Authors
C¸i˙ftc¸i˙, Emi˙n
Hogan, John P.
Kolayli˙, Hasan
Cadirli, Emin
Issue Date
2008
Type
Article
Language
Keywords
Periodicals , Geology , Eastern Turkey , Kop Mountains , Listvenite , Metasomatism , Natrolite , Natrolitite , Pargasite , Zeolites
Alternative Title
Natrolitite, An Unusual Rock - Occurrence And Petrographic And Geochemical Characteristics (eastern Turkey).
Abstract
Very unusual rocks consisting of natrolite (>95 vol.%) ? pargasite(< 5 vol.%) and rareal bite (<1 vol. %) have been discovered in the Kop mountain range, eastern Turkey. We propose to call these rocks ‘natrolitite’ and ‘pargasite natrolitite’. They were produced by Na Si metasomatism of dikes and stocks of diorite through replacement of the intermediate primary igneous plagioclase to produce natrolite. The metasomatic alteration produced concentric elliptical zones characterized by distinct mineral assemblages centered on intrusions of diorite. The Central Zone 1 consists of variably albitized diorite with preserved magmatic textures (albite ? andesine ? pargasite ? quartz). Transition Zone 2 comprises natrolite-bearing diorite (natrolite? albite? andesine? pargasite? calcite? quartz). Marginal Zone3 is a rock madeup almost entirely of natrolite (natrolite? pargasite? albite? calcite? chlorite). Outer Zone4 occurs along the boundary between the natrolitite and the surrounding serpentinite and consists of listvenite, a rock which comprises magnesite, quartz, calcite, mica, talc, and hematite, indicating a role for CO2 in the metasomatic reactions, consistent with the presence of calcite in the alteration zones. Zone 5 consists essentially of brecciated serpentinite with numerous hydrothermal quartz veins and calcite veins. Whole-rock compositions document an increase in Na2O, Al2O3, and H2O from thecore(c entral zone) to themargin while CaO, MgO, and SiO2 decrease. Plagioclase abundance and composition also varies outwards from the central core rocks where it occurs as a primary magmatic phase (~95 vol.% An41-38) to the alteration zones (<5 vol.% An32-37) due to partial to complete replacement of plagioclase by natrolite with or without rare albite. The natrolites exhibit little variation in Si/Al ratios, ranging between 1.45 and 1.61, and are similar in composition to those reported in the literature. Accompanying pargasitic amphibole also becomes progressively more sodic in composition from the core rocks to the marginal zone rocks. Our analysis indicates that albitization preceded the formation of natrolite and that the formation of natrolite, instead of other more typical alteration minerals (e.g. analcime and paragonite), reflects Na metasomatism at lower chemical potentials for Al2O3 and SiO2. Potential sources of Na could be hypersaline brines or leaching of country rocks, such as trondhjemites. The fluids were driven in hydrothermal convection cells set up by the intrusion of the diorites.
Description
Clays and Clay Minerals, Vol. 56, No. 2, 207–221, 2008. Natrolitite, An Unusual Rock - Occurrence And Petrographic And Geochemical Characteristics (eastern Turkey). Emin Ciftci; John P. Hogan; Hasan Kolayli; Emin Cadirli. DOI: 10.1346/CCMN.2008.0560206. Copyright © 2008, The Clay Minerals Society.
Citation
Clays and Clay Minerals, Vol. 56, No. 2, 207–221, 2008.
Publisher
The Clay Minerals Society
License
Copyright © 2006-2018, The Clay Minerals Society