In situ Rb-Sr dating of K-bearing minerals in the Gonen granitoid from the western Sakarya Zone, NW Anatolia

Granitoids with ages ranging from Paleozoic to Tertiary are widely distributed in the western Sakarya Zone. The Gonen granitoid is one of these Paleozoic (Early Carboniferous) granitoids and exposed on the western part of the Sakarya Zone in NW Anatolia. The Gonen granitoid is unconformably overlain by the Jurassic Bayırkoy Formation consisting of conglomerate, sandstone, siltstone, and claystone intercalation. Medium to coarse-grained, yellowish brown-colored Gonen granitoid chiefly made up of K-feldspar, plagioclase, muscovite, quartz, and biotite. In this paper, it is presented in situ Rb-Sr isochron ages for the Gonen granitoid in the western Sakarya Zone. The isochron derived from muscovite and plagiocalse minerals occurring in the granitoid yielded 299.3 ± 3.4 Ma (Late Carboniferous), which is interpreted as the emplacement age of the Gonen granitoid. This study also testifies that radiometric in situ Rb-Sr dating can be applied to resolve absolute dating of magmatic complexes. According to the initial 87Sr/86Sr ratio, the magma producing the Gonen granitoid was derived from the enriched subcontinental lithospheric mantle forming the ancient crust. The Carboniferous magmatic event can be attributed to the northward subduction of the Palae-Tethys oceanic crust along the southern margin of Laurasia in the Early-Late Carboniferous.