Electronic probe instrument is an instrument for quantitative chemical analysis of single mineral micro-area, and it is widely used. In recent years, due to the rapid development of computer network technology and the accelerated development and use of related application software, the new generation of electronic probes equipped with high-precision spectrometers have digital features, artificial intelligence and automated analysis procedures, network functions and High-resolution image collection and analysis and processing capabilities. At the same time of analyzing the composition, it can carry out the analysis of the morphology and structure of the mineral micro-area, and truly realize the electronic probe chemical dating technology is a technology that is being developed and applied in geosciences to determine the age. The United States and Japan and other countries Scholars have done some exploratory research work on this technology. This study intends to first determine the age of monazite, zircon and other minerals containing L-Th-Pb and use their oxide components to determine their age. It is of great significance for studying the source rocks of clastic rocks and river sediments, the evolution history of multi-stage and multi-stage structures, volcanic activity, etc. 1 Basic principles and age calculation The following is based on the radioactive elements in monazite based on electronic probes Oxide determination of LTh and Pb to explain the basic principles and age calculation of electronic probe chemical dating. A series of a. The above radioactive series can establish the decay of L and Th isotopes as direct when establishing a long-term equilibrium state in geological history. There are three independent equations for conversion to the corresponding Pb isotope: If the atomic number of PbTh and L of radioactive origin is known, then: the atomic number of PbTh and U of radioactive origin is converted to its corresponding oxide PbOTh2 and The UO2 quality score data by Williams et al. And Corfu ’s research shows that the monazite contains a very small amount of primary and Koppel ’s studies relative to the amount of radioactive Pb. 6, the monazite generally shows consistent U-Pb and The isotope age of Th-Pb, that is, the content of Pb in w (primary Pb) 0 monazite is proportional to the time since its formation. We use the following equation to The results of the electronic probe analysis of the group ThO2UO2 and PbO are calculated for ThOS2: then the formation age of the monazite can be obtained by the following simple formula: find it by the iterative method, and after calculation, iterate 18 times to meet the age accuracy requirement, ie t1t2 … T17t18 Of course, during the test, some factors such as monazite, zircon, and other minerals that affect the accuracy of the dating must be corrected, such as the mutual interference between the rare earth element lines, and finally make it It can reflect the actual age of solitary stone formation. At present, it is very easy to realize the above calculation with a computer program.
2 The reliability of the electronic probe chemical dating technology as a new dating technology should be fooled by its guess. The reliability is based on the reliable netbookmark analysis and verification of the UI Ma isotope from the North Mashan granite in Hunan. There are differences in annual accuracy. For example, the accuracy of MichaelL.W. Et al.'S calculation of age can be estimated by the above-mentioned dating equation, using the transferable characteristic X-ray counting error. For the monazite (w>%) of the pre-Cambrian system rich in Th, the accuracy is calculated by counting statistics on one day. KazuhuMie et al. Yanjiezheng bookmark2 Since the 1990s, China's desertification has become increasingly serious. Sandstorms have occurred almost every year, and the capital, Beijing, has also suffered greatly. To this end, find the source of sand and dust, and take corresponding measures to control the sand dust source area to the relevant geomorphological data and remote sensing technology to determine the source area of ​​sand and dust and provide a set of basic geological data on sandstone evolution for desertification control.
3.3 Judging the source rocks of sediments in rivers and other water systems, the monazites taken from the Liaohe sand samples in China were measured, and the ages of 288 monazites were measured, of which 19 were concentrated in the range of 2500M, which is cut through with the Liaohe River. The ancient Craton region in Northeast China is actually related to the fact that the Liaohe Group is the Lower Proterozoic (250 (± ~ 1800Ma), and this part of the monazite is likely to come from it. It is used to determine the source rock of river and other river sediments It can provide the geological basis for the source rocks of the rivers and rivers that control sedimentation. For the management of the Yellow River and other rivers, first of all, the roots of the sediments should be traced to understand the formation, evolution and transportation history of the source rocks. Evaluation of the electronic probe chemical dating technology in recent years, the electronic probe chemical dating technology of monazite has been successfully applied to the study of magmatic rocks. It has obvious advantages compared with traditional isotope methods (such as mass spectrometry) , But there are also shortcomings. The advantages are mainly: (1) It is fast to analyze and easy to test, the required sample volume is small and does not damage the sample. Each time the analysis of the main elements of monazite only takes a few Minutes (after calibration), the analysis of trace elements takes about 10 minutes; (2) Traditional dating methods are generally time-consuming and costly, while the cost of electronic probe chemical batch dating is low; (3) Electronic probes Dating can determine and locate the core and edge of the monazite separately, and make the crystallographic position of the crystal correspond to the calculated age. The high spatial resolution smaller than the microbeam allows us to be in a small range ( A few micrometers) to carry out a large number of analytical tests on the samples, check the age and composition heterogeneity or ring structure, and can describe their formation process and characteristics, providing us with a large amount of age and related information. In this regard, traditional isotopes The dating method is incomparable, and its main disadvantages are: (1) Compared with ion probe or mass spectrometry dating methods, its accuracy and sensitivity are one order of magnitude lower and its uncertainty is usually between 2 ... 50Ma. Therefore, samples younger than 100Ma are rarely dated by this method; (2) This method takes the w (primary Pb) 0 of monazite, and the original Pb of the wrong stone is not zero in some cases, although the age The necessary corrections are made in the calculation, but it also affects the accuracy of this method of dating. In addition, if the zircon selected from the same sample has different physical properties, such as different electromagnetic properties, colors, density, and crystal form, etc., reflect its The physical and chemical environment at the time of formation and the subsequent changes are different; when testing with this method, it should be determined separately according to the specific conditions to distinguish zircon under different genetic conditions and the geological events it has experienced, which has increased to a certain extent. Workload; (3) The selection and preparation of standard samples are very high. It is worth noting that a large amount of age data can be obtained by this method, which can be divided by statistical methods when the number of samples (age data points) is sufficient For a long time, the age value is also closer to the true value. From the statistical results, it can be roughly determined to which age region the age data point falls. Different age regions represent different eras and geological events experienced.
Take the corresponding 9 measures. In fact, the rnalmectronic electronic probe chemical dating technology is a supplement to traditional dating methods such as isotopes. It provides a summary of rapid age determination. The dating data can be used as a more detailed isotope dating method. basis. In many cases, its dating results can be mutually confirmed with the age results of traditional dating methods such as isotopes.
Prospective technology, while measuring the mineral composition, also obtained the chemical age and mapping. Comrade Bao Xuezhao from Tianjin Geological and Mineral Research Institute provided us with the Beimasan sample and its isotope age data. Dr. Yokoyama of the National Geological Museum of Japan provided some test results. Comrade Li Xiaobo also helped, and I would like to thank you here!
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