碱性长石中Al—Si分布的计算方法讨论——以江西相山及山东七宝山火山-侵入杂岩为例

碱性长石的结构状态是其温压条件,特别是冷却速率的反映。对碱性长石的结构态,目前国内均是采用X-射线衍射资料中060峰及204峰的2θ值来求解的,但单斜晶系的碱性长石204峰常被其它峰叠覆。Hovis(1989)在对碱性长石的X-射线衍射资料作系统研究的基础上,提出了用113峰及060峰来计算单斜碱性长石不同四面体位置Al占位率的方法。本文分别利用上述两种方法(即利用060峰、204峰的方法和利用113峰、060峰的方法)对相山及七宝山火山—侵入杂岩中存在较大冷却速率变化梯度的碱性长石进行了系统的结构态研究

METHODS FOR DETERMINING THE Al-Si DISTRIBUTION IN ALKALI FELDSPAR --A case study of volcanic-intrusive complexes at Xiangshan and Qibaoshan

The structural state of alkali feldspar is a reflecation of its temperature-pressure conditions and, in particular, its cooling rate. Analysis of shifts of diffraction maxima as a fuction of structure and degree of Al-Si order reveals that peaks are most useful for the estimate of Al-Si distribution directly from X-ray data. The 060 and 204 powder-diffraction maxima are in common use in China. For monoclinic alkali feldspars, although the 060 peak is suitable for use, the 204 peak is overlapped by other peaks. Based on a systematic analysis of X-ray powder-diffraction data of alkali feldspar of various series, Hovis proposed a method to determine Tl and T2 site occu-pacies of monoclinic feldspars by use of the 2(9 value of the 113 and 060 peaks from X-ray data. In this paper, the authors utilize the two methods to calculate the structural states of alkali feldspars from the volcanic-intrusive complexes of Xiangshan and Qibaoshan. Comparison of the results reveals that the Al-Si distribution obtained by using the value of the 060 and 113 peaks is more accordant with the geologic case than that obtained by using the 060 and 204 peaks.