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Laser Probe Ar-Ar Geochronology Applied in Mn Oxides for the Reconstruction of Paleoclimate and Paleoenviroment Study

会议论文信息

期刊名称：	Laser Probe Ar-Ar Geochronology Applied in Mn Oxides for the Reconstruction of Paleoclimate and Paleoenviroment Study
责任者：	谭娟娟；杨红梅；卢山松
关键词：
会议名称：	国际地质大会 International Geological Congress
届次：	35
会议地点：	南非
召开时间：	2016-08
论文集名称：
ISBN：
项目资助信息：
摘要：	Laser probe has been used in Ar-Ar geochronology since the 1970s.Due to its high orientation,high energy intensity,high onsistency and the ability to be modified accurately,it is especially useful in Ar-Ar dating when it comes to the samples with young age,low K contents or small amounts.Apart from the traditional K-rich samples such as biotite,muscovite and K-feldspars,more and more minerals could be utilized in Ar-Ar geochronology for the purpose other than age determination for mineralization and metamorphism,but also for environmental re-search including reconstruction of paleoclimate and paleoenvironment.Li et al.(2004) [1] summarized the ability of manganese oxides as the objects of Ar-Ar dating,suggesting that the key problems are K contents and the maintenance of radiogenic Ar,which are caused by mineral species,composition of weathering fluids and the crystal structures of minerals.Combined with other research results on crystallography including the TEM research [2-3],the manganese oxides with tunnel structures such as cryptome-lane are most suitable for Ar-Ar dating.However,unlike the other minerals for Ar-Ar dating (micas,mphiboles,etc),the challenge with dating manganese oxides starts from the mineral seperation process.As it is difficult to pick out the samples by gravity or magnetism,hand picking is necessary,so it requires the combination of optical microscopy study and EMPA analysis for both high K content and high purity of the samples.Vasconcelos et al.[4] for the first time applied K-Ar and Ar-Ar dating methods to manganese oxides in Brazil,and the Ar-Ar age yield by laser fusion was concordant with the K-Ar age by step-heating within the er-ror,suggesting the time when weathering process took place.From then on,more geochronology study on man-ganese oxides has been done for paleoclimate reconstruction. 37 samples from 10 areas in Europe provide an age range concentrating between 25 Ma and 1Ma of Miocene,suggesting the removal of Mn elements take place under subtropical humid environment.Another case of precise age constraints in a Mn deposit from Yunnan,China provides the growing rate of Mn ore veins:given the Ar-Ar plateau age,it can be calculated that the growing rate of Mn nodules is faster than other reported Mn deposits worldwide by 1 to 2 orders of agnitudes [5],suggesting the difference in fluid pressure during the ore-forming process.De Putter et al.[6] studied the Kisenge Mn deposit in Congo and their results of Ar-Ar ages illustrating a tendency that the deeper the location is,the younger the samples,showinga response to the uplift of East African platform and the following formation of East African Rift.
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