Provenance analysis of early-middle jurassic clastic rocks in the Gümüşhane area (ne Turkey) based on petrographic and geochemical properties

In this study, Early–Middle Jurassic sedimentary rocks in the Gümüşhane area have been investigated in terms of their lithological, petrographical and geochemical features. In this contex, four stratigraphic section were measured around the Akçakale, Bağlarbaşı, Gurbetyatağı and Yukarıalıçtı, and sampled especially in terms of clastic rocks. The lithologic features of the Measured Stratigraphic Sections (MSS) of Akçakale, Bağlarbaşı and Gurbetyatağı are similar, they are usually composed of sandstone, mudstone, limestone and chert intercalated and their thicknesses were measured as 95 m, 127 m and 133 m, respectively. Yukarıalıçtı MSS is conglomerate at the base continuing upwards into sandstones, marl, limestones and volcanic rocks. This series continues until 375 meters and then it passes to volcanic rocks. Grain size average of the investigated sandstones range from -0.78 – 2.50 ɸ and the sandstones are very coarse–fine-grained according to Wenthworth scale. Sandstones of the Akçakale MSS are arkozoic arenite, greywacke, the Bağlarbaşı MSS are greywacke, the Gurbetyatağı MSS are litarenite and feldispathic wacke-greywacke, the Yukarıalıçtı MSS are lithic arenite and feldispathic wacke-greywacke in mineralogical composition. Major element contents of the sedimentary rocks of the Akçakale, Bağlarbaşı, Gurbetyatağı and Yukarıalıçtı MSS are nearly similar. The highest average SiO2 content with 57.67 % belong to samples from the Bağlarbaşı MSS, the lowest average SiO2 content with 52.67 % at Akçakale. Based on their chemical composition, most of the samples of the Akçakale, Bağlarbaşı, Gurbetyatağı MSSs are classified as wacke, some of samples of Yukarıalıçtı MSS are wacke, others are shale-Fe shale. The trace and rare earth element (REE) contents and their distributions in the sedimentary rocks from all the sections are nearly similar. Basic/felsic–intermediate/felsic provenance for the investigated sedimentary rocks deduced from their major, trace and rare earth element geochemistry. These rocks are probably derived from Carboniferous Gümüşhane pluton (granite and granodiorite) and early Jurassic Gokcedere pluton (gabbro) according to mixed source composition model. Chemical Index of Alteration (CIA) values vary between 35-74, 39-84 and 38-89 for Akçakale, Bağlarbaşı and Gurbetyatağı MSS, respectively. These CIA values indicate a low-an intensive chemical alteration, in the source areas of the investigated rocks. The CIA values for Yukarıalıçtı MSS range from 30 to 51, and suggest a low chemical alteration in the source areas of the Yukarıalıçtı MSS sandstones and marl. In addition, geochemical data suggest a relatively simple cycling history for the studied rocks. Akçakale, Bağlarbaşı and Gurbetyatağı rocks are similar to those deposited in passive margin setting, whereas Yukarıalıçtı MSS are typical for arc setting and they were likely deposited in a back-arc setting.