Geochemistry of the Middle Jurassic sediments in Gümüşhane, north-eastern Turkey: Implications for weathering and provenance

The whole-rock geochemistry and Sr-Nd isotope data of Middle Jurassic sedimentary rocks in the Gümüşhane area (north-eastern Turkey) were analysed to reconstruct the provenance, chemical weathering, sediment recycling history, and tectonic setting of the source area. Based on trace element ratios and rare earth element (REE) patterns, it was interpreted that the sandstones were derived from a source area with felsic-mafic rocks as dominant contributors. The average chemical index of alteration (CIA) and weathering index (WIP) values are low with respect to Upper Continental Crust (UCC) in the studied sandstones and mudstones, but the index of compositional variability (ICV) values are high, thus revealing weak–moderate weathering conditions. The average Th/U ratios of the sandstones and mudstones indicate a relatively simple cycling history. The positive and low negative εNd values support the supposition that the source area did not undergo much sedimentary change. A model mixture composed of 60% granite, 5% granodiorite, and 35% gabbro could be deduced to be the potential source composition of Middle Jurassic sediments; this model was reinforced by the 87Sr/86Sr ratios and εNd(t) values of the sediments. The Middle Jurassic siliciclastic sedimentary rocks of the Gümüşhane region were likely deposited in a tectonic environment with a passive margin.