Geochemical and isotopic signatures of the early jurassic acidic rocks (Olur-Erzurum)

The Early Jurassic Coşkunlar Dacite and Güvendik Trondhjemite, subjected to this study, crop out an area of approximately 50 km2 in the 5 km south of Olur (Erzurum). The rocks with tholeiitic character include mainly quartz and plagioclase, small amounts of K-feldspar and opaque, zircon and apatite secondarily. LA-ICP-MSI-U-Pb zircon dating reveals that the Coşkunlar Dacite has a cooling age of 184.1 Ma, whereas Güvendik Tondhjemite has a cooling age of 185.34 Ma. Samples have a strong peraluminous character (A/NK = 1.18-2.00 - A/CNK 0.98-1.94). Rare earth element contents of the acidic rocks show low to moderate (LaN/YbN= 0.92-7.57) fractionations and moderately negative Eu anomalies (Eu/Eu*= 0.39-0.80). In addition, the rocks present a moderate enrichment in large ion lithophile elements (LILE) relative to the high field strength elements (HFSE). The rocks have low to moderately radiogenic 87Sr/86Sr(i) (0.70513-70978) and 143Nd/144Nd(i) (0.51235-0.51260) isotope ratios, and slightly positive ƐNd (-0.055-+3.8126) values. Pb isotope ratios are in the range of 206Pb/204Pb(i)= 14.53-19.58, 207Pb/204Pb(i)= 15.43-15.69 and 208Pb/204Pb(i)= 31.2-39.65. Trends shown in major and trace elements and strong peraluminous characteristics show that fractional crystallization has played an important role in the formation of rocks. Tholeiitic nature (K2O<%2.63) of the rocks points out that they might have been formed from a relatively more basic (andesitik/tonalitic) magma through fractional crystallisation. The low to moderately raiogenic Sr, Nd, and Pb isotope ratios indicate that the rocks might have been originated from a basic tholeiitic source by partial melting.