锆石平均阳离子半径的变化趋势及其在判别形成环境中的意义

计算了变南成因和岩浆成因锆石从晶体核部至边缘的平均离子半径,发现它们的变化存在规律性,作者认为这种规律性同锆石结晶时岩浆或母岩的温夺条件变化密切相关,论述了用锆石平均阳离子半径变化趋势来判别其结晶ＰＴ条件变化趋势的方法及可能性。

AVERAGE CATION RADIUS R VALUE OF ZIRCONS AND ITS SIGNIFICANCE IN EXPLAINING THE VARIATION OF FORMATION TEMPERATURE AND PRESSURE OF ZIRCONS

The structure zoning trends are discovered in magmatogenic and metamorphogenic zircons.The structure parameter is obtained by calculating the average canon radius R value of zircons,which can be expressed in the formula: (canon number×catinn radius) cationnumber. It has been proved that the R value is directly proportional to the unit cell volume in an individual crystal. The fact discovered in this paper suggests that: 1. in magmatogenic zircons, the decreasing of R from inner to outer portion of each growth zoning or from core to rim of a crystal indicates the gradual lowering of magma temperature during crystallization; the increasing in Rvalue indicates the gradual decreasing in magma pressure during crystallization. 2. in metamorphiczircons, the higher the metamorphic grade of protolith, the larger the average R value of the metamorphogenic zircons isn in individual crystals, from core to rim the R value has a rising trend, which indicates that the temperature of protolith mainly rises during the growth of metamorphogenic zircons.