نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه ژئوشیمی، دانشکده علوم زمین، دانشگاه خوارزمی، تهران، ایران
2 موزه شهاب سنگهای ایران، تهران، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
Introduction
Meteorites are of interest to researchers as materials that have stored the history of the creation of the universe. However, the petrology of meteorites has received less attention in our country. In this research, two pieces of meteorites discovered in the Shahdad desert, located in the southwest of Lot Valley, have been subjected to petrographic and geochemical studies. The report of the discovery of this meteorite in 2018 was recorded in the World Bulletin. At present, there is a considerable diversity of topics within meteorite research. In addition, extensive petrographic and geochemical studies are being conducted in the field of classification and petrology of these rocks. In general, extensive and specialized research in this field is carried out in most of the world's leading universities, including European and American scientific centers (e.g., the Meteorite NASA Center and the G-Time Laboratory of the University of Brussels). The studied meteorite is also the largest chondritic meteorite discovered in Iran. This makes the subject of this study particularly important from the research point of view. The primary objective of this research is the petrographic and geochemical classification of the meteorite. Two pieces of the meteorite, which constitute a portion of a larger meteorite with an estimated mass of approximately 90 kg, were discovered in an area spanning 5 square kilometers in the western region of the Lut Desert and in the vicinity of Shahdad City in Kerman Province.
Materials and Methods
The hand sample of meteorites from the Lut Desert in Iran displays a surface that is completely dark in color, ranging from dark brown to black. It contains regmaglypts and tension fractures resulting from impact with the Earth's surface. A thin melted crust, measuring 0.1 millimeters in diameter, covers the sample's surface. This crust reveals a fresh stone surface with a light brown color and gray to light brown speckles. The chondrules, which are known to be speckles, have a diameter ranging from 0.2 to 0.5 millimeters, with a density of 60 to 75 percent of the hand sample's surface (Figure 3 a).
The thin 0.1 mm diameter melt shell covers almost the entire surface of the sample. The presence of pyroxene and olivine compounds in the studied meteorite indicates that this sample belongs to the group of ordinary chondrites (OC) and is classified in the group of L and LL chondrites. The internal texture of the chondrules suggests that this meteorite belongs to the POP and BO groups, which are associated with meteorites that experienced high temperatures and cooling rates of 1000 to 1500 degrees per hour. Three pieces of this rock were crushed and powdered by hand for the purposes of chemical analysis.
Results and Discussion
The presence of pyroxene and olivine compounds in the studied meteorite indicates that this sample belongs to the group of ordinary chondrites (OC) and is classified in the group of L and LL chondrites. The internal texture of the chondrules indicates that it belongs to the POP and BO group, which is related to meteorites with high temperature and cooling rates of 1000 to 1500 degrees per hour. The diagram of Al/Mn vs. Zn/Mn ratio (Figure 6) illustrates the locations of different types of common chondrites and typical examples of chondrites (known chondrites from around the world) (Kallemeyn et al, 1991, 1994, 1996, 1978, 1989; Kallemeyn and Wasson, 1982). The blue circles in this figure represent the Shahdad meteorite. The composition of the silicates and the chondrule boundaries of the studied meteorite indicate a fourth type of petrology. Given the absence of visible oxidation of metal or sulfide in the sample and the presence of a lemon-colored spectrum, it can be inferred that the degree of weathering is W0. In the majority of the examined sections of olivine crystals, a series of planar and irregular fractures on the olivine surface and plate fractures in the pyroxene mineral can be observed, which is indicative of remelting.
Conclusion
According to the comparison of column charts of trace elements related to Shahdad meteorites with typical Antonin chondrites (L4-5). The composition of the elements of these two groups of meteorites are similar with a slight difference, which is a confirmation of the common chondrite of the L5 type of Shahdad meteorites. The classification of Shahdad meteorites by geochemical diagrams based on the amount of silica and alkaline elements and the diagram of alkaline elements (Na2O, K2O) versus silica indicates that Shahdad meteorites are alkaline. According to all the available evidence, the body of the mother asteroid of L5 Shahdad chondritic meteorites is a normal chondrite S asteroid type.
کلیدواژهها [English]
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