Application of the Crosta technique for alteration mapping of granitoidic rocks using ETM+ data:: case study from eastern Tauride belt (SE Turkey)

The present study particularly focuses on the determination of alteration products of the granitoid associations by remote sensing techniques. Widespread magmatism has occurred in the Malatya-Elazig. area of the eastern Tauride belt in south east Turkey as a consequence of plate convergence and continental collision. The development of the magmatism in the study area can be subdivided into two separate phases, the Baskil and the Bilaser Tepe complexes. Based on the petrographic and bulk-rock geochemical data, the Baskil granitoids are classified as quartz-diorite, quartz-monzodiorite and tonalite, whereas the Bilaser Tepe granitoids are classified as granodiorite and dacite-porphyry. Both the Baskil and Bilaser Tepe granitoids have peraluminous and metaluminous compositions. The Crosta method is found to be very useful for enhancing the altered areas with hydroxyl and iron oxide minerals. The Crosta method is applied to six ( 1, 2, 3, 4, 5 and 7) and two sets of four ( 1, 3, 4, 5 and 1, 4, 5, 7) bands of ETM+ data. However, the areas with potassic, phyllic, argillic and propylitic alteration zones are enhanced much better by using six bands of Landsat 7 ETM+ data. The alteration differences of these two magmatic groups are also tested with the Crosta technique using four band combinations. Although no distinct difference is observed on the hydroxyl image, a clear difference is observed between the two magmatites on the iron oxide image. The present study shows that the Crosta technique is not only generating hydroxyl and iron oxide images, but also differentiates between two magmatite groups of different ages and genesis.