Clays and Clay Minerals, Vol. 54, No. 3, 333-350, 2006.
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Authors
Yalcin, Huseyin
Bozkay, Omer
Issue Date
2006
Type
Article
Language
en_US
Keywords
Periodicals , Geology , Hydrous Phyllosilicates , Isotopes , Major Elements , Ophiolite , REE , SEM , Trace Elements , XRD
Alternative Title
Mineralogy and Geochemistry of Paleocene Ultramafic- And Sedimentary-hosted Talc Deposits in the Southern Part of the Sivas Basin, Turkey
Abstract
Talc deposits, located mainly in three areas of north-central Turkey, are present in the ophiolitic series of the Cretaceous and in siliciclastic rocks of the Paleocene. Talc deposits related to ophiolites are between tectonite and cumulate occurring as beds and/or lenses and 0.1-3 cm thick fracture fillings within a 5 m brecciated zone with a vein-type bedding. Sedimentary-hosted talc beds and semi- rounded to angular talc grains (0.1-2 cm) range in thickness from 0.1 to 30 cm within marls and conglomerates. Talc veins form lenses (a few meters long) and spheroidal and/or ellipsoidal nodules (1-10 cm). Calcite, dolomite, serpentine and/or mixed-layered illite-smectite (I-S) minerals are encountered in the talc samples. Serpentine with positive U and Hf anomalies, and talc with positive Nb and Zr anomalies, and negative Ta and Ce anomalies are typically depleted in P and Ti, based on chondrite- normalized trace element patterns. The light rare earth element content of sedimentary-hosted talc with a negative Gd anomaly is richer than those of ultramafic-hosted talc with a negative anomaly for Eu as well as serpentine. Significantly, talc with a uniquely sedimentary origin tends to be the principal source of Nb, Hf, Zr, La, Ce, Pr and Nd with respect to serpentine. d18O and dD values for talc range from +13.8 to +17.5% and -60 to -36%, and those of serpentine are +9.4 and -88%, indicating supergene conditions for sedimentary-hosted talc and hypogene for ultramafic-hosted talc. When compared with seawater, d18O data indicate temperatures of 68ëC and 80-98C for the sedimentary- and ultramafic-hosted talc formations, respectively, and 100C for serpentine, suggesting that talcification and serpentinization of ultramafic rocks both occurred at nearly the same time with various stages. All data show that the talc occurrences are divided into two types based on their mode of formation. The first corresponds to a serpentinization stage within the ophiolites. The others are the neoformation products of sedimentary deposition, diagenetic and post-diagenetic processes, respectively. Sedimentary-hosted talc also seems to have inherited trace element and isotopic compositions from the parent ultramafic rocks.
Description
gsccm-54-3-05-yal.pdf 3.42MB PDF/A Document.
Citation
Clays and Clay Minerals, Vol. 54, No. 3, 333-350, 2006.
Publisher
The Clay Minerals Society
License
Copyright © 2006-2018.