Alteration Mineralogy and Geochemistry of the rocks from Tekirova (Antalya) Ophiolite Nappe

Abstract

The Tekirova Ophiolite Nappe, part of the Antalya Unit in the southwest Anatolia, consists of a dismembered oceanic crust sequence with tectonic slices in different sizes. Three types of subsequent mineralizations are present in the ophiolitic rocks during the oceanic crust formation, emplacement and post-emplacement, respectively. First stage, pyrometamorphism (pyrometasomatization) caused to occurrence of metamorphic minerals such as scapolite, diopside, garnet, epidote and tremolite. Second stage, hydrothermal metamorphism(alteration) is represented byserpentinization of ultramafic rocks. Third stage is followed by listwaenite formation, and age neoformation and/or alteration products contain carbonates (calcite, dolomite, aragonite, magnesite, hydromagnesite, hydrotalcite), oxides and hydroxides (brucite, goethite, hematite), phyllosilicates (smectite, illite, chlorite, talc, C-V, C-S, I-S) and quartz. The serpentine minerals can be distinguished from each other by morphology: ribbon-like shapes for antigorite, platy for lizardite and fibrous for chrysotile. Serpentines are represented by three polytypes as structural groups of A- (clinochrysotile-2M(1)), C- (lizardite-1T) and D- (lizardite-2H(1)). Chondrite-normalized trace and rare earth element patterns of 1T and 2H(1) Fe-lizardites, Fe-tremolite and Ca-hydromagnesite minerals show similar trends indicating similar ophioliticparent rocks and differentiated form each others. The delta O-18 and delta D values of serpentines indicate two different serpantinization under hypogene conditions as oceanic (lizardite-1T) and supergene as Alpin types (clinochrysotile-2M(1) and lizardite-2H(1)) at temperatures of about 200 degrees C and 100 degrees C, respectively.