Abstract
In Northwest Anatolia, widespread magmatism developed due to collision between Anatolide-Tauride platform and Sakarya continent during Late Cretaceous-Early Tertiary period. The granitoids in Biga Peninsula are products of post-collisional magmatism following the convergence of the northern branch of Neotethyan Ocean and developed in two different stages as Eocene and Oligo-Miocene. Eocene Karabiga, Gureci, Kuscayir and Dikmen granitoids are granite and diorite-granodiorite; Oligo-Miocene Sarioluk, Yenice, Kestanbol, Eybek, Evciler, Camyayla and Alankoy granitoids are diorite, granodiorite, monzonite and Q-monzonite in composition. Metaluminous and peraluminous granitoids have similar geochemical variations and exhibit post-collisional geochemical signatures. Trace element patterns are almost similar to those observed in upper crust and GLOSS (Global Subducting Sediment) patterns with depletion in high field strength (HFS) elements (Nb, Ta, Ti, Zr, Hf). But, Oligo-Miocene Sarioluk, Yenice-Cakiroba, Kestanbol, Evciler, Camyayla, Alankoy and Eocene Karabiga, Gureci and Kuscayir granitoids have higher Th and U contents relative to upper crust and GLOSS. Dikmen, Yenice-Hamdibey, Yenice-Eskiyayla and Eybek granitoids have lower Th content. Geochemical variations indicate that partial melting and fractional crystallisation- crustal contamination processes are effective in their genesis and evolution. Trace element ratios also indicate subduction signatures in their genesis and Rb/Ba, Rb/Sr ratios suggest mantle melting rather than crustal melting. Accordingly, post-collisional Biga Peninsula granitoids were derived from a previously metasomatised lithospheric mantle source, which was enriched during northward subduction and closure of the northern branch of Neo-Tethys Ocean beneath the Sakarya continent, since variations in Rb, Cs, Th, La and Sm reveal that lithospheric mantle was mesomatised by both aqueous fluids and sediment melts.
Highlights
Regional GeologyThe Late Cretaceous-Early Eocene period was a tectonically active period and Tethyan evolution was effective in Western Anatolia with ophiolite emplacement, high pressure/low temperature metamorphism, subduction, arc magmatism and continent-continent collision processes occurring (Okay et al, 2001)
As the Biga Peninsula is a region where subduction, continent-continent collision and postcollisional processes may be observed, it forms a good area to research geochemical dynamics of magmatism and to reveal the effects of these processes on the genesis and the evolution of the magmatism
Trace element variation diagrams, trace and rare earth element (REE) distribution patterns indicate that the Biga Peninsula granitoids were affected by fractional crystallisation processes during the evolution of the magmatism
Summary
The Late Cretaceous-Early Eocene period was a tectonically active period and Tethyan evolution was effective in Western Anatolia with ophiolite emplacement, high pressure/low temperature metamorphism, subduction, arc magmatism and continent-continent collision processes occurring (Okay et al, 2001). Pre-Tertiary basement rocks outcrop within NE-SW striking tectonic zones (Duru et al, 2012). These zones are the Çetmi melange, Ezine zone and Sakarya Zone from west to east (Figure 1b). The Ezine and Sakarya zones are overlain by the Upper Cretaceous-aged Çetmi Melange (Duru et al, 2012) (Figure 1b) These pre-Tertiary basement rocks in the study region, magmatic and sedimentary rocks occurred during the Eocene-Quaternary time interval were emplaced (Duru et al, 2012; Ilgar et al, 2012). Alanköy granitoid represented by granodioritic rocks has well developed skarn zones and Q-stockworks as well
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