|
چکیده
|
The present study provides systematic petrographical and geochemical analyses of the Neogene continental successions of the Eshtehard area to investigate their tectonic setting, provenance and paleoclimate condition, and recycling effect. The Neogene successions are subdivided into five stratigraphic units (M1 to M5). Eighteen medium- to coarse-grained sandstone and 22 mudstone samples were selected from the Mard Abad, Eshtehard, Rud Shur, and Salt Mine sections in the Eshtehard area (NW Central Iran Structural Zone). A combined study of petrography (point-counting method) and geochemistry (ICP-MS) has been carried out in this study. The ternary diagrams (QtFL, QmFLt, and LmLvLs) for detrital modes and the discrimination diagram reveal that the studied samples from the unitsM1 toM5 were deposited in a back-arc basin. The Ti/Zr vs. La/Sc bivariate diagramand La-Th-Sc, Th-Co-Zr/10, and Th-Sc-Zr/10 triangular diagrams indicate that mudstones from the Neogene continental deposits in the Eshtehard area were potentially derived from intermediate igneous rocks. The low CIA (55.78 to 69.36) and Cvalues (0.27 to 0.53) of mudstones together with their position in A-CN-K and SiO2 vs. (Al2O3 + K2O + Na2O) plots indicate weak to moderate chemical weathering of the source material in arid to semi-arid paleoclimate conditions. The Neogene siliciclastic deposits in the Eshtehard area were derived from intermediate igneous source rocks within a back-arc basin north of the Urumieh–Dokhtar magmatic arc.
|