Amphibole-melt Dihedral Angle in the Process of Melt-crystallization of Trachybasalt: Effects of Temperature and Pressure(PDF)
《地球科学与环境学报》[ISSN:1672-6561/CN:61-1423/P]
- Issue:
- 2016年第03期
- Page:
- 341-354
- Research Field:
- 基础地质与矿产地质
- Publishing date:
Info
- Title:
- Amphibole-melt Dihedral Angle in the Process of Melt-crystallization of Trachybasalt: Effects of Temperature and Pressure
- Author(s):
- ZHAO Dong-yu; ZHANG Bo; HU Xian-xu; FAN Da-wei; ZHOU Wen-ge; XIE Hong-sen
- 1. Key Laboratory for High Temperature and High Pressure Study of the Earth’s Interior, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, Guizhou, China; 2. University of Chinese Academy of Sciences, Beijing 100049, China
- Keywords:
- dihedral angle; melt-crystallization; trachybasalt; high pressure and high temperature; interface energy; impingment texture; textural equilibrium; textural evolution of magma
- PACS:
- P589.1;P586
- DOI:
- -
- Abstract:
- The mineral-melt dihedral angle is a very important parameter to further understand the crystallization kinetics and the textural evolution of magma. Using trachybasalt as the starting material, two series of melt-crystallization experiments (temperature series and pressure series) were conducted at the pressures of 0.6-2.6 GPa, the temperatures of 800 ℃-900 ℃ and the annealing time of 100 h, to investigate the influence of temperature and pressure on the mineralmelt dihedral angle. In the temperature series (3 groups), trachybasalt were fused at the temperature of 1 350 ℃, the pressure of 0.6 GPa and the annealing time of 1 h, to obtain homogeneous melts; then, the melting temperatures dropped to the crystallization temperatures of 800 ℃, 850 ℃ and 900 ℃, and annealed for 100 h. In the pressure series(4 groups), the trachybasalt were fused at the temperatures and pressures of 1 350 ℃ and 0.6 GPa, 1 375 ℃ and 1.1 GPa, 1 400 ℃ and 1.6 GPa, 1 425 ℃ and 2.1 GPa, and 1 450 ℃ and 2.6 GPa, respectively; the samples were kept under such conditions for 1 h to ensure completely melting and proper homogeneity, and then the temperatures dropped to the crystallization temperature of 900 ℃ and annealed for 100 h. Amphibole was the main crystal phase in the process of trachybasalt crystallization under the above experimental conditions. The amphibole-melt dihedral angles from the experimental products were obtained by measuring the dihedral angles in the two-dimensional random sections. The effects of temperature and pressure on the dihedral angle were discussed by comparing the observed cumulative frequency of the amphibole-melt dihedral angles in the run products with the theoretical cumulative frequency curve. The median of apparent dihedral angles in amphibole-melt increases with the increase of temperature. The nucleation density of amphibole is small while the growth rate is fast at high temperature; thus, the higher temperature is beneficial to the growth and coarsening of amphibole, so that the grains impinge and form the high dihedral angle. Conversely, the nucleation density of amphibole is large while the growth rate is slow at low temperature; therefore, the low temperature impedes the growth and coarsening of amphibole, and results in the parallel grains with the small dihedral angle. Moreover, the median of amphibole-melt apparent dihedral angles increases initially, then reduces and finally increases again with the growing pressure, the possible reason is the prominent difference in mechanical properties between the melt and minerals. It is proved that the mineral-melt dihedral angle gradually increases with the development of mineral from isolation to impingement texture in the early stage of magma crystallization. Furthermore, combined the result of this study with the previous work about the evolution of mineral (or mineral-melt) dihedral angle in the late stage of magma crystallization, the evolution trend for the mineral-melt dihedral angle in the whole process of magma crystallization can be inferred.
Last Update: 2016-06-02