• 文章目录 •

### 锆石柱面中Hf、Y的配位差异性及其对晶型的控制效应

1. 南京大学 地球科学系， 江苏 南京 210093
• 收稿日期:2000-06-20 修回日期:2000-06-20 出版日期:2000-06-20 发布日期:2000-06-20

### Different Coordination between Hf4+ and Y3+ on Prismatic Faces of Zircon and Its Morphological Constraint

ZHOU Dong-shan, WANG Xiang

1. Department of Earth Sciences, Nanjing University, Nanjing 210093
• Received:2000-06-20 Revised:2000-06-20 Online:2000-06-20 Published:2000-06-20

Abstract: The morphology of naturally grown zircon does not simply confor mto Ha rtman's PBC theory. It is often affected by the physical parameters such as grow th temperature, diffusion coefficient etc. Furthermore, it is ubiquitously restr icted by the anisotropic growth retardarce as the result of the anisotropic subs titution of various ions. After semi-quantitative analysis on {100} and {110} p rism faces, it can be found that the number of chemical bonds between Hf4+ or Y3+ and O2-- on {100} face （n{100} ） differs from that of {110} face (n{110}), and that the streng th of Hf-O, Zr-O and Y-O declines orderly. Because the growth of zircon is ge nerally slow enough, it can be assumed that local equilibrium exists between magmaticmelt and various single crystals during crystallization of zircon. Using the general therm odynamic equation of energy and concentration, the concentration difference of H f4+ and Y3+ ions on {100} and {110} faces can be formulated as: Cx{110}/Cx{100} = A{100}/ A{110}exp[(n{100}-{110})/RT×（EX-O – EZr-O）/RT] where X refers to Hf4+ or Y3+ ions, Zr refers to Zr4+ ions, O refers to O2- ions, E refers to the energy of the chemical bonds between the subscript ions, C and n refer to the concentration. o f subst itutional ions and number of formed chemical bonds on the subscript crystal face respectively. A is related to growth mechanism of zircon, but its differenc e between {100} and {110} faces of zircon is generally small enough to be ignore d. Thus, the concentration difference is mainly determined by the difference in coordination structure of zircon crystal faces and the difference in energy of c orresponding chemical bonds. 　　When reference data of the energy for Hf-O, Zr-O and Y-O bonds are cited, it can be drawn that Hf tends to enrich itself on {100} face, while Y tends to enrich itself on {110} face. As the result of growth retardarce of the impurity ions, { 100} will be preferentially developed in Hf-rich ziron, while {110} will be pre f erentially developed in Y-rich zircon, which agrees well with previous statisti c s. Finally, as the anisotropic substitution of Hf and Y on {100} and {110} is de pendent on the temperature strongly and with a concise mathematical correlation, a potential geothermometer based on the above relation is proposed.