| 激光显微探针40Ar/39Ar 定年方法研究 |
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| 关键词:laser microprobe 40Ar/39Ar dating |
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| Reserch on laser microprobe 40Ar/39Ar dating |
| Our laboratory has successfully developed a laser microprobe 40Ar/39Ar geoloical dating technique,the technical principle of which is to find the measuring mineral on a piece of polished rock section (1-2mm thick)under a high-power microscope and then to introduce the pulsed laser beam into the light path of the microscope through a prism and to focus it on the surface of the mineral making the latter melting. Ar gas thus released is used for dating.Our research includes feasibility study for the method within China,adjustment of the high-gaining electron multiplier in a mass spectrometer,adjustement of the laser,test for absorbability of samples to laser,designing and manufacturing high-vaccum sample melting chamber,sample processing,research on sample irradiation and J values,detecting atmosphric argon,blank and age, exploration and optmization of experimental circuit,etc.Experimental results show relatively close coindidence of laser microprobe 40A/39Ar ages with conventional ones.The BSP-1 amphibole international standard ages determined though repeated measurements range mainly between 2020-2090 Ma and most of the ZBH-25 domestic standard ages obtained through repeated meaurements in granite in Zhoukoudian are between 130-135.9Ma.The analysis area can be minimized to less than 30μm in diameter(and the laser itself can be focused within limits of less than 10μm in diameter).Investigations indicate that the laser microprobe technique supplies an extremcly prospecting tool for following researches:(1)measurement of the age for samples which are difficultly collected in large quantity; (2)research on the age for rocks that are of cmoplex Ar regime because of the effect of multiphase events in geologic history;(3)research on the age of those minerals infilling various textural positions in rock samples and comparing data from inside of every crystal grain and between different grains; and(4) measurement of the 40Ar/39Ar age for young K-rich samples. It is clear that the laser dating plays particular role in research on structural,metamorphic and mineral deposit chronologies. |
| CHEN Wen,LUO Xiu-quan,ZHENG Bao-ying,ZHANG Si-hong.1994.Reserch on laser microprobe 40Ar/39Ar dating[J].Acta Geoscientica Sinica,15(1,2):197-205. |
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