Relationship between chemical composition and magnetic susceptibility in the alkaline volcanics from the Isparta area, SW Turkey

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Potassium-rich volcanic rocks in the Isparta area (SW Turkey) consist mainly of older (Pliocene) volcanic rock suites (e.g., lamprophyre, basaltic trachyandesite, trachyandesite, trachyte) and younger (Quaternary) caldera forming lava dome/flows (e.g., tephriphonolite, trachyte) and pyroclastics (ash/pumice fall deposits and ignimbritic flows). The magnetic susceptibility (K) was performed for both groups. The magnetic susceptibility value of the less evolved rocks characterized by SiO2 < 57 wt% (e.g., basaltic trachyandesite, tephriphonolite, lamprophyric rocks) and having mostly mafic phenocrysts such as pyroxene, amphibole, and biotite-phlogopite is over 10 (10−3 [SI]). Fine to medium-grained and subhedral to anhedral opaque minerals are scattered especially in the matrix phase of the less evolved volcanic rocks. However, the K value of the more evolved rocks (e.g., trachyte and trachyandesites) with SiO2 over 57 wt% vary between 0.1 and 28, but most of them below 10. SI values are negatively correlated with SiO2, Na2O, but positively correlated with Fe2O3, CaO, MnO, P2O5 and MgO contents, suggesting inverse variation of SI with fractionation of potassic magma. That is to say that less evolved volcanic rocks have relatively higher magnetic susceptibility values in the volcanic suite. Fine to medium-grained and subhedral to anhedral Fe-Ti oxides are scattered mainly in the matrix phase of the less evolved volcanics, presumably cause the pronounced relatively higher magnetic susceptibility.