Abstract

In this study, chlorite is used to investigate the diagenetic-metamorphic evolution and accurate geological history of the different units belonging to the Karakaya complex, Turkey. Primary and secondary chlorite minerals in the very low-grade metamorphic rocks display interference colors of blue and brown and an appearance of optical isotropy. Chlorites are present in the matrix, pores, and/or rocks units as platy/flaky and partly radial forms. X-ray diffraction (XRD) data indicate that Mg-Fe chlorites with entirely IIb polytype (trioctahedral) exhibit a variety of compositions, such as brunsvigite-diabantite-chamosite. The major element contents and structural formulas of chlorite also suggest these were derived from both felsic and metabasic source rocks. Trace and rare earth element (REE) concentrations of chlorites increase with increasing grade of metamorphism, and these geochemical changes can be related to the tectonic structures, formational mechanics, and environments present during their generation.

Highlights

  • Chlorite is a typical rock-forming mineral present in very low grade facies of metamorphic rocks.Chlorite may originate from aggradation following the evolution of neomineralization of trioctahedral smectite → interlayered smectite-chlorite (C-S) → chlorite, which implies prograde metamorphism due to burial and subsequent diagenesis

  • Isotropiclike chlorite minerals in the matrix are observed in porphyroblasts that form in tremolite-rich metabasalts of the LKC-UP, which formed under greenschist facies conditions (Figure 2b)

  • Chlorite within the units of the Karakaya Complex representing NW and NE Anatolia are of neoformed origin in the groundmass and/or matrix and pores, and display different optical properties and morphologies

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Summary

Introduction

Chlorite may originate from aggradation (positive transformation) following the evolution of neomineralization of trioctahedral smectite → interlayered smectite-chlorite (C-S) → chlorite, which implies prograde metamorphism due to burial and subsequent diagenesis. It represents degradation (negative transformation) in igneous rocks from trioctahedral mica and ferromagnesian minerals, and residual and authigenic minerals in sedimentary rocks [1]. The most significant mineralogical and chemical changes/transformations in chlorite occur during burial diagenesis/metamorphism (e.g., [2,3,4,5,6,7,8,9,10,11,12,13]). The utility of chlorite is demonstrated relative to the interpretation of the diagenetic-metamorphic evolution of the different units within the Karakaya complex

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