五大连池老黑山火山钾质玄武岩结晶动力学研究

Study on crystallization dynamics of potassic basaltic lava of Laoheishan volcano in Wudalianchi area,NE China

本文模拟了五大连池地区老黑山火山钾质响质碱玄岩熔岩在不同降温速率下从1150℃冷却到700℃橄榄石的结晶动力学过程,并从晶体粒度、晶体数量和晶体形态三方面研究了晶体结晶特征与降温速率之间的关系。结果表明:(1)晶体粒度分布(CSD)显示七组不同降温速率下的晶体粒度与布居密度均呈现较好的幂率关系,且幂律指数相近,斜率范围在3.69~4.42之间,这说明了晶体粒度分布对降温速率的依赖性并不显著。(2)随着降温速率由快变慢,晶体数量总体增长。当降温速率为0.0468℃/min时,晶体数量达到峰值。随后,结晶进入以退火合并为主的晶体粗化过程,直至结晶动力学达到平衡。(3)各降温速率下晶体形态呈现出分形特征,分形维数界于1.39~1.62之间,反映了新生晶体生长的自组织临界性。不同降温速率下的晶体边界复杂程度出现较大无规波动,显示出晶体形态对降温速率的高度敏感性。当降温速率为0.1℃/min时,晶体边界形态最复杂,当降温速率变慢到0.0468℃/min后,晶体边界形态的复杂程度趋于稳定。本项动力结晶实验对于深入了解五大连池新期火山熔岩流的运动机制以及动力结晶过程有重要的科学意义。

This work simulates the dynamic crystallization process of the potassic phonotephritic lava from Laoheishan volcano,Wudalianchi at different cooling rates from 1150℃to 700℃.The relationship between crystal crystallization characteristics and cooling rate was studied from three aspects,namely,crystal size,crystal number and crystal morphology.The results show that:(1)The crystal size distribution(CSD)reveals that the relationship between crystal size and number density at the seven cooling rates show the characteristics of good power law.The exponent of power law is almost the same,ranging from 3.69 to 4.42,as indicates that the crystal size distribution does not significantly depend on the cooling rate.(2)As the cooling rate decreases from fast to slowly,the total number of crystals generally grows.When the cooling rate is 0.0468℃/min,the number of crystals reach a peak.Then,the crystals enter the Ostwald ripening process,and the crystallization is mainly the process of annealing and merging until the kinetics reaches equilibrium.(3)The crystal morphology has fractal characteristics at various cooling rates,and the fractal dimension is between 1.39 and 1.62.The complexity of crystal boundary at different cooling rates shows large random fluctuations,which reveals the strong sensitivity of crystal morphology to the cooling rate.When the cooling rate reaches 0.0468℃/min,the complexity of crystal boundary tends to be stable.The internal correlation between crystallization characteristics and cooling rate is of scientific significance for realizing the movement mechanism of lava flows in Laoheishan volcano and their dynamic crystallization mechanism.