The origin of carbonatites from the eastern Armutlu Peninsula (NW Turkey)

Abstract

Unusual carbonate dykes, which have a thickness of up to 4 meters, crosscut the amphibolites from the high-grade metamorphic rocks in the Armutlu Peninsula (NW Turkey). They are described as carbonatites based on their petrographic, geochemical, and isotope-geochemical characteristics. The carbonatites, which show commonly equigranular texture, are composed of calcite and clinopyroxene with other minor phases of plagioclase, mica, garnet, K-feldspar, quartz, epidote, titanite, and opaque minerals. They contain abundant xenoliths of pyroxenite and amphibolite. Geochemical characteristics of the carbonatites are significantly different from those of mantle-derived carbonatites. They have remarkably low incompatible elements (e.g. Ba, Th, Nb) and total REE contents (11-91 ppm) compared to mantle-derived carbonatites. The high 87Sr/86Sr(i) (0.70797-0.70924) and low εNd(t) (-8.08 to -9.57) of the carbonatites confirm that they were derived from the continental crust rather than from a mantle source. Mica from carbonatite was dated by the 40Ar/39Ar method and yielded Late Jurassic – Early Cretaceous (148-137 Ma). This age is significantly younger from the age (Upper Triassic) of adjacent amphibolites. All data from field studies, as well as petrographic, geochemical and geochronological observations, suggest that these carbonatites were formed from the anatectic melting of a carbonated source area in the continental crust.Supplementary material: A complete description of the analytical methods (Whole rock chemistry, mineral chemistry, Strontium and Neodymium isotopes and 40Ar/39Ar measurements) and mineral chemistry and 40Ar-39Ar dating results are available at https://doi.org/ 10.6084/m9.figshare.12946955