准噶尔盆地老山沟火山岩晶体粒度分布及其结晶动力学意义

摘　 要　 阐述了火山岩晶体粒度分布的基本原理和研究方法‚分析了老山沟火山岩斜长石、 辉石、橄榄石、铁钛氧化物的晶体粒度分布。前3种矿物在中间粒度处发生了有意义的弯折‚ 原因是岩浆上升时过冷度增大。估算了岩浆房中斜长石、橄榄石的成核速率、结晶时间及上 升过程中处于结晶带的时间。研究表明‚在岩浆的演化过程中‚晶体的分离和累积作用及岩 浆的混合和对围岩的同化作用可以忽略。

CRYSTAL SIZE DISTRIBUTION IN VOLCANIC ROCKS IN LAOSHANGOU OF JUNGGAR BASIN AND SIGNIFICANCE OF CRYSTALLIZATION KINETICS

The theory and method of crystal size distribution (CSD) are expounded and the size distributions of crystals of plagioclase, olivine, pyroxene and opaque minerals in volcanic rocks in Laoshangou of Junggar basin are analyzed. Significant bends occur in middle size for the first three minerals. A nearly horizontal trend of CSD for large size of minerals represents those crystals which nucleate in magma chamber. The straight line trend whose slope is negative for small size of minerals represents those crystals which nucleate during magma ascent. The authors ascribe the bend to the variation of undercooling. The variation of undercooling influences the nucleation rate more than growth rate of crystal, so the population density increases during magma ascent. After choosing an appropriate growth rate of crystal, the nucleation rate and crystallization time of crystal in magma chamber and the time in crystallization field during magma ascent can be estimated. During the evolution process of magma, there are not crystal fractionation and accumulation, crystal nuclei destruction, and magma mixing and assimilation with surrounding rocks.