The relationship between collisionrelated calcalkaline, and within-plate alkaline, volcanism in the Karacadag( Area (Konya, Central Anatolia)
Résumé
The Karacadag (Kulu-Konya) area is one of the main volcanic provinces in Central Anatolia. The Karacadag volcanites are composed of large volumes of andesitic-dacitic lavas associated with pyroclastics and small volumes of alkali basalt, trachybasalt and trachyandesite lavas. Two groups of volcanic rocks can be distinguished: (1) calcalkaline rocks including andesites and dacites, and (2) alkaline rocks including basalts, trachybasalts and trachyandesites. 40Ar/39Ar ages show that the Karacadag volcanites were erupted during Early Miocene (ca.1819 Ma) and suggest that alkaline volcanites succeed shortly afterwards calcalkaline volcanites. Major oxides and trace elements plotted versus SiO2 suggest fractionation of hornblende, FeTi oxide and apatite for calcalkaline volcanic rocks and olivine, clinopyroxene and FeTi oxide for alkaline volcanic rocks in the magmatic evolution. The incompatible trace element patterns of the calcalkaline volcanites show enrichment of LILEs (Sr, K, Rb, Ba and Th) and negative HFSEs (Nb, Ta) anomalies suggesting an enriched lithospheric source by a subduction-related process. On the other hand, alkaline volcanites show enrichment of both LILEs and HFSEs suggesting an enriched lithospheric source by small volume melts from the asthenosphere. The rocks also have moderately fractionated REE patterns with (La/Lu)N ratios of 724 for calcalkaline and 617 for alkaline volcanites. Moreover, the volcanites have relatively low 87Sr/86Sr(t) ratios for between 0.703782 and 0.705129, and high eNd(t) values between +2.25 and +4.49. Generally, the SrNd isotopic compositions of the rocks range from the mantle array to bulk earth. All of these observations and findings suggest that the calcalkaline volcanites were formed in a subduction modified orogenic setting, and the alkaline volcanites in a within-plate setting.