پاورپوینت ژئوشیمی عناصر نادر خاکی در سنگ فسفاتی رسوبی (pptx) 47 اسلاید
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بسم الله الرحمن الرحیم موضوع: ژئوشیمی عناصر نادر خاکی در سنگ فسفاتی رسوبی
Introduction:
During recent years, geochemistry of rare earth elements (REEs) has proved to be one of the best tools for determining conditions of depositional environments and understanding of formation mechanism of sedimentary phosphatic rocks, and hence has received worldwide attention by many researchers.
Distribution patterns of REEs and variations of anomaly values of Eu and Ce in phosphatic sedimentary rocks are highly dependent upon various factors including conditions of the depositional environment and the degree of interaction between seawaters and land-derived detrital materials (Khan et al., 2012).
Factors like weathering, diagenesis, and metamorphism can remarkably influence the concentration of REEs and their distribution patterns in phosphatic rocks (McArthur and Walsh, 1984).
The results of recent researches revealed that geochemical investigations of REEs in sedimentary phosphatic rocks can furnish valuable information on paleo-seawaters and/or diagenetic fluids (e.g. Shields and Stille, 2001; Zhu et al., 2014; Muscente et al., 2014; Xin et al., 2016; Auer et al., 2017; Zhu and Jiang, 2017).
The phosphatic sedimentary deposits in Iran were developed temporally in six discrete periods: (1) Spatially, thLower Cambrian, (2) Ordovician-Silurian, (3) Upper Devonian, (4) Upper Cretaceous, (5)Paleocene, and (6) Eocene-Oligocene. ese deposits are widely spread within five structural zones: (1) Central Iran, (2) Alborz-Azarbaidjan, (3) Gorgan-Rasht, (4) Folded Zagros, and (5) Sanandaj-Sirjan (Namadmalian et al., 1998).
The Lower Cambrian phosphatic deposits in the Gorgan-Rasht Zone contain an average of 11 wt% P2O5 and reserves exceeding 66 million tons (Namadmalian et al., 1998), and extend over 60 km with varying thicknesses between 2.2 and 5 m.
Mineralogically, the principal constituent minerals present in these deposits are calcite, fluor-apatite, dolomite, quartz, pyrite, muscovite, and illite (Abedini et al., 2012).
The Soltanieh Formation (Neoproterozoic-Lower Cambrian) is widely exposed in the Gorgan-Rasht Zone (northern Iran) and host to the phosphatic sedimentary deposits.
Up to now, extensive stratigraphic, paleo-biologic, sedimentary, and geochemical (carbon stable isotopes) investigations were carried out in the Soltanieh Formation in an attempt to determine the conditions of depositional paleo-environment during the period of Neoproterozoic-Lower Cambrian by different researchers (Hamdi et al., 1989; Brasier et al., 1990; Kimura et al., 1997).
So far, comprehensive studies concerning geochemical characteristics and behavior of rare earth elements during evolution of the phosphatic rocks of the Soltanieh Formation have not been done.
The aim of this work is to study the distribution patterns of REEs, variations of Eu and Ce anomaly values, and elemental ratios as useful means for appreciating the paleo-seawater conditions and diagenetic environments during phosphatization of the Lower Cambrian phosphatic rocks of the Soltanieh Formation in the Vali- Aabad area of northern Iran.
Geological setting and studied section:
Based upon the structural division of Iran (Nabavi, 1976), the study area is located in the central part of the Gorgan-Rasht Zone (Fig. 1).
The stratigraphic units, from the oldest to the youngest, in the study area (see Fig. 2) include Neoproterozoic Kahar Formation (slaty shale, sandstone, siltstone, dolomite, and quartzite), the Neoproterozoic-Lower Cambrian Soltanieh Formation (dolomite and shale), the Cambrian Barut Formation (siltstone and shale), theCambrian Ziagun Formation (shale and siltstone), the Cambrian Lalun Formation (Sandstone), and the Carboniferous Mobarak Formation (limestone, dolomite, and intercalated marl). These successions are overlain by the Upper Permian basic igneous lavas, pyroclastics and sandstone. The Quaternary alluviums are the youngest lithologies in the area.
