| 碱性玄武岩形成的时限及其地质意义 |
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| 关键词:time limit of the formation of alkaline basalts isotopic and element geochemistry history state evolution of the Earth from hot to cold |
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| The Time Limit of the Formation of Alkaline Basalts and Its Geological Signifance |
| The alkaline basalts do not occur in the early precambrian in the North China Craton and itsneighbouring area. The restriction in their forming-time is also a world-scale phenomenon. Theyare predominanlly formed after the Mesozoic. There are two types of the alkaline basalts , namelythe potassic and the sodic. The later can be further divided into normal and abnormal ones. Theirisotopic and element compositions change gradually each other , prabably caused by the variation ofthe types and proportion of the material adding into the mantle source regions. High presure and lowdegree of melting appear to be the necessary requirements for the formation of the alkaline basalts.It is suggested that the restriction in the form ing-time of the alkaline basalts is mainly related to thehistory state evolution of the Earth from hot to cold. supposed to be needed for the formation Of al-kaline basalts ,the mantle subduction could atlain sufficient depth only after the Archaean ,andmight great depth post Mesozoic. |
| WAN Yu-sheng,WU Jia-shan,DI Yuan-sheng.1995.The Time Limit of the Formation of Alkaline Basalts and Its Geological Signifance[J].Acta Geoscientica Sinica,16(4):365-374. |
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