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GENETIC SIGNIFICANCE OFHIGH-TEMPERATURE EXPERIMENTS ON IGNEOUS ROCKS

Zhou Xun-ruo, Bai Zhi-min   

  1. China University of Geosciences,Beijing 100083
  • Received:1999-03-20 Revised:1999-03-20 Online:1999-03-20 Published:1999-03-20

Abstract: This paper puts emphasis on the genetic significance of some high-temperature experiments with volcanic rocks, intrusive rocks, meteorites and dark hydrous minerals as initial experimental materials.On the basis of layering of the melting crust of chondrite and the glass,a discussion is made on the layer structure of terrestrial planet and the forming mechanism of volcanic rocks during the early period of the earth and moon rocks.On the basis of the melting sequence of minerals from acidic volcanic rocks during dry melting and wet melting,an analysis is made on the acidity evolution of granitic magma during intrusion and the genesis of light-colored granulite.In addition,a discussion is also ma de on the relation of melting point,acidity and structure of rocks.According to the melting experiments of basalt with added granite,the authors exclude the possibility of formation of leucite basalt through assimilation of basaltic magma by granitic magma,and suggest the possibility of forming tholeiitic series rocks with Large straddle trend through fractional crystallization of high-aluminium basaltic magma and alkali picritic magma.By calculating the viscosity of melt at different acidities and different temperatures,the authors illustrate the relationship between the acidity, viscosity of melt and volcanic phase,eruption and volcano types,and point out that at the same temperature,the larger the acidity,the higher the viscosity increasing rate. The correlation is made between the melting experiments of fresh basalt and basalt with weak spilitization, metamorphism and weathering. It proves that the compositions of these rocks,as long as their original microstructures are preserved, can be taken as the criteria for rock type and series classification and rock nomenclature. By using the method of basalt melting-crystallization experiments, the relationship is studied between the course of mineral crystallization,the degree of supercooling, the nucleation of melt and the growth rate of crystals. The mineral assemblage and evlution sequence as well as their significance are investigated during the cooling course of leucite picritic melt. According to the heating experiments of dark hydrous minerals,an interpretation is given to the course of their changes such as oxidation,dehydration and thermo-optical characteristics, and to their stages of changes such as darking, resolution and melting. A discussion is made on the application of these results to geothermometer and phased division of igneous rocks. The pressure effect and quenching effect of calcium-rich clinopyroxene is also studied especially its changes in TiO2 and A1203 contents. The authors point out that isothermal effect may exist for calcium-rich clinopyroxene.