Exhibition of lanthanide tetrad effect in PAAS-normalized REE patterns, and non-CHARAC (non-CHArge-RAdius Control) behavior of Y/Ho and Zr/Hf in limestone of the Ruteh Formation, Kanigorgeh district (NW Iran), were studied in order to understand the reasons of occurrence of lanthanides tetrad effects. The computed values show that the third and fourth tetrads can be used as a good and powerful geochemical tool for investigation of physicochemical conditions of the depositional environment of the limestones. Here, a new mathematical-based method using polar coordination system for tetrad effect values (Tp) was used to evaluate under studying limestone. The correlation between Tp and some geochemical parameters revealed that the limestone was likely deposited under two different conditions. The obtained results indicated that paleo-redox conditions, adsorption and scavenging by kaolinite and metallic oxides, degree of detrital input, diagenesis intensity, and complexation by polycarbonate ligands are likely the main mechanisms for occurrence of tetrad effect phenomenon in REE distribution patterns in the limestone. This means that tetrad effect phenomenon in REE distribution patterns of limestone can be applied as a good geochemical indicator to evaluate the deposition conditions in limestones., Ali Abedini, Mansour Rezaei Azizi and Ali Asghar Calagari., and Obsahuje bibliografii
The Kanisheeteh bauxite deposit (NW Iran) is located on the Irano-Himalaya karst bauxite belt and was developed as stratiform horizon along the contact of the Permian and Triassic formations. Based on absolute weathering index (AWI), HREE were leached out, whereas LREE suffered both leaching and fixation during bauxitization. The non-CHARAC characteristic of Y/Ho ratios can be attributed to geochemically known phenomenon as the "tetrad effect". The simultaneous convex and concave curves of the tetrad effect were observed in the chondrite-normalized REE patterns of the bauxite ores. The correlation between the sizes of T4 and AWI% values revealed two separate populations. The first one is characterized by a wide variation in sizes of T4 and very narrow AWI% values, and is thought to be related to acidic zone of the profile. In contrast, the second one is marked by a narrow variation in sizes of T4 and wide variation in AWI% values, and is conceived to be affiliated to alkaline zone of the profile. In this research, the tetrad effect proved to be capable of clarifying the geochemical characteristics of the deposit and can be applied as a good geochemical index to investigate the prevailed paleo-conditions of depositional environments.