Mineralogy and petrology of leucite ankaratrites with affinities to kamafugites and carbonatites from the Kayikoy area, Isparta, SW Anatolia, Turkey: Implications for the influences of carbonatite metasomatism into the parental mantle sources of silica-undersaturated potassic magmas

摘要

In the Kayikoy area of Isparta-Golcuk district, Inner Isparta Angle, SW Anatolia, Turkey, a small volume of newly discovered K-rich mafic potassic magma was emplaced in the form of dome in the vicinity of graben structures under Pliocene (3.68 +/- 0.5 Ma) extensional tectonics. Kayikoy leucite ankaratrites are made up of abundant diopside, barian phlogopite and leucite, and lesser olivine, that rarely contains Cr-spinel, nepheline and hauyne, with abundant magnetite. They have low SiO2 (44.00-46.04 wt.%) and Al2O3 (12.10-12.64 wt.%) with high K2O (4.00-4.42 wt.%), CaO (13.50-14.40 wt.%) and MgO (8.52-9.36 wt.%), with high Cr (397-547 ppm) and moderate Ni (57-74 ppm) contents. They represent the less evolved silica-undersaturated mafic potassic magmas within the Isparta-Golcuk volcanic province, and may be considered another parental source to the wide spectrum of the K-rich rocks. They are highly enriched in most of the incompatible elements (e.g., Ba, 2761 to >10,000 ppm; Sr, 3700-4074 ppm; Th, 33.60-36.99 ppm; Zr, 274-321 ppm) with high LREEs, low HREEs and elevated LREEs/HREEs ratios [(La/Yb)(N), 73-80] and are comparable with kamafugite and carbonatites. Trace element patterns have negative P, Ti and Nb-Ta anomalies in common with the Italian kamafugite province and lack of a Eu anomaly, in contrast to the negative Eu anomaly of the Italian province. Their Sr-87/86-Nd-143/144 (0.703877-0.512765) isotopic compositions, together with those of other potassic volcanics from the Inner Isparta Angle, coincide with the West Quinling (China) kamafugites with highly depleted mantle signatures, and young East African carbonatites. Olivine-Cr-spinel pairs, high Mg# (0.69-0.73) numbers and Cr values, and high incompatible and LREE contents in Kayikoy leucite ankaratritic magma are consistent with near-primary magmas equilibrated with enriched and heterogeneous (peridotitic/pyroxenitic) mantle sources. On the basis of (i) their geochemical signatures [low Ti/Eu, elevated CaO/Al2O3 and (La/Yb)(N) ratios], (ii) consistency of parental magma compositions with experimental melt compositions for carbonated peridotites, and (iii) geochemical and isotopic affinities to kamafugites and carbonatites, it is inferred that the carbonatitic melts infiltrated the mantle sources of Kayikoy leucite ankaratritic magma, and induced the depletion of its SiO2 contents. Carbonate-bearing phonolitic parental melts formed by mixing of both silicate and carbonate-asthenospheric melts from convecting mantle, react with wall-rock peridotite to form diopside + phlogopite + olivine + apatite metasomatic veins as wehrlitic metasomes. Partial melting of such newly generated wehrlitic metasomes in the subcontinental lithospheric mantle resulted in the parental melts of Kayikoy leucite ankaratrites. Results also imply that the nature and composition of asthenosphere-derived silicate melts (basanitic, phonolitic or tephriphonolitic in composition) and percentage of mixed carbonatitic melts lead to the formation of discrete mantle metasomes within the Inner Isparta Angle lithospheric mantle. These metasomes are conducive to the generation of coeval potassic magmas with contrasting geochemical signatures (e.g, lamproitic, lamprophyric, kamafugitic) in a single tectonic setting. (C) 2016 Elsevier B.V. All rights reserved.