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Fluids along the North Anatolian Fault, Niksar basin, north central Turkey: Insight from stable isotopic and geochemical analysis of calcite veins

Sturrock, Colin P.
Catlos, Elizabeth J.
Miller, Nathan R.
Fall, Andras
Gabitov, Rinat I.
Yılmaz, İsmail Ömer
Larson, Toti
Black, Karen N.
Six limestone assemblages along the North Anatolian Fault (NAF) Niksar pull-apart basin in northern Turkey were analyzed for delta O-18(PDB) and delta C-13(PDB) using bulk isotope ratio mass spectrometry (IRMS). Matrix vein differences in delta O-18(PDB) (-2.1 to 6.3 parts per thousand) and delta C-13(PDB) (-0.9 to 4.6 parts per thousand) suggest a closed fluid system and rock buffering. Veins in one travertine and two limestone assemblages were further subjected to cathodoluminescence, trace element (Laser Ablation Inductively Coupled Plasma Mass Spectrometry) and delta O-18(PDB) (Secondary Ion Mass Spectrometry, SIMS) analyses. Fluid inclusions in one limestone sample yield T-h of 83.8 +/- 7.3 degrees C (+/- 1 sigma, mean average). SIMS delta O-18(PDB) values across veins show fine-scale variations interpreted as evolving thermal conditions during growth and limited rock buffering seen at a higher resolution than IRMS. Rare earth element data suggest calcite veins precipitated from seawater, whereas the travertine has a hydrothermal source. The delta O-18(SMOW-fluid) for the mineralizing fluid that reproduces T-h is +2 parts per thousand, in range of Cretaceous brines, as opposed to negative delta O-18(SMOW-fluid) from meteoric, groundwater, and geothermal sites in the region and highly positive delta O-18(SMOW-fluid) expected for mantle-derived fluids. Calcite veins at this location do not record evidence for deeply-sourced metamorphic and magmatic fluids, an observation that differs from what is reported for the NAF elsewhere along strike.