蚀变普通角闪石微结构研究

ELECTRON MICROSCOPIC ASPECTS OF ALTERED HORNBLENDE

澳大利亚驼峰山岩体中普通角冈石的高分辨电子显微象，显示了一系列水热蚀变产生的云辉闪石系的显微结构。这些结构体在角闪石晶体中沿（010）方向生长，无序分布，链体的宽度各不一致，最常见的链体宽度是3，4，5，6链体，更宽的链体结构比较少见。大量观测结果表明，这些云辉闪石结构体多产生在角闪石颗粒边缘、晶体破裂面和解理面周围。不同宽度链体之间可以发生相互置换，置换可以是协调式的，也可以是非协调式的。协调式置换即当链结构体置换时，没有位错或其他形式的破裂产生。非协调式置换为链结构体转换时伴随着角闪石晶格的错裂。错裂是分位错形式，主要沿角闪石的三个方向：1／4[010]，1／2[100]和1／2[100]＋1／4[010]，而错裂面的延伸是平行角闪石的解理面。非协调式置换的错裂产生更为宽阔的通道，促进蚀变反应进行具有更重要的意义。

Hornblende in mafic monzonite sampled at Narooma, N. S. W., Australia, has been studied by high resolution electron microscopy (HRTEM), revealing a variety of pyribole intergrowth microstructures as a result of hydrothermal alteration. These pyriboles occur in hornblende crystals as chain-width disordered defects (also called 'zippers'). In many cases the terminations of the defects are topotactic with respect to amphibole structure, and continuous along (010), having relatively large vacancies where chain-widths change, which thereby provide diffusion avenues. The vacancies in three dimensions appear as tunnels running parallel to the Z-axis of hornblende having minimum 0. 5nm diameters while some can be as large as about (5 ×20)× 10-2nm2. The occurrence of the defects appears to be random, most commonly as 3, 4, 5 and 6 chain-widths, in rare cases as 7 and 10 chain-widths. The defects are commonly observed in association with grain bound-aries, crystal fractures and cleavages.In many other cases, the pyribole defects are terminated in association with the formation of planar faults which common1y extend along (110). Three types of planar defects have been found in regard to their displasive directions: 1/4 [010], 1/2 [100] and 1/2 [100] + 1/4 [010] as referred to a hornblende unit cell. These microfaults may play a very important role in controlling the speed of modifying hornblende structure and chemistry into various chain-width disordered defects.