Akademik Veri Yönetim Sistemi
CLAY MINERALS, cilt.38, sa.4, ss.529-550, 2003 (SCI-Expanded)
In the area of Sile, NW Turkey, Upper Cretaceous calc-alkaline volcanic rocks with compositions ranging from andesite to rhyolite have been recognized. The most widespread rocks of the suite are andesites, which can be grouped into altered and fresh. The oldest altered andesites are the parent rocks for the kaolin deposits of the Study area. The Upper Cretaceous volcanic suite consists of spilite, basalt, andesite, trachyandesite, trachyandesitic and hyaloandesitic dacite, rhyolite lavas, tuffs and agglomerates. The highly altered andesites are composed of plagioclase, pyroxene, hornblende, biotite, augite and very fine opaque minerals. During the Turonian, all E-W trending extensional magmatic are was developed in the Istanbul Tectonic Zone of the oceanic Western Black Sea basin and intermediate volcanic rocks were emplaced, mostly calc-alkaline andesites, suggesting multi-stage magmatism. The significant features of the andesites are: (1) enrichment of LILE (Rb, Ba, K) over HFSE (Zr, Nb, Hf, Ti, Th, U, Y) and LREE (La-Sm), resulting in high Ba/Nb, Th/Nb, Ba/La, K/Ti and Th/La ratios; (2) depletion of LREE over HFSE, MREE and HREE, generating high La/Nb, Ce/Ti, La/Sm and La/Y values; and (3) depletion of Nb, Sr and Ti, all of which are typical of island arc magmatism, with possible back arc signature. The Th-Hf-Ta diagram for tectonomagmatic classification shows that the Sile calc-alkaline rocks are similar to volcanic rocks from the Mariana Arc, the Aeolian Arc of Salina, Italy, the Skaros island in the Aegean Sea and Sardinia's ignimbrites. Moreover, relatively low La/Th and Ce/Pb ratios suggest that the source region of volcanism was enriched in LILE with respect to REE, indicating crustal contamination during melting.