Homogenizacja i dekrepitacja w badaniach temperatury powstawania minerałów i skał

Jadwiga Pawłowska

Abstract


HOMOGENIZATION AND DECREPITATION IN STUDIES ON CRYSTALLIZATION TEMPERATURES OF MINERALS AND ROCKS

Summary

Studies on the crystallization temperatures of minerals and rocks have been initiated at the Geological Institute, Warsaw. The homogenization of the inclusions is examined by means of "Boetius" heating stage adapted for this purpose, the decrepitation by means of equipment constructed at the Geological Institute. The aim of the present paper is to present the experience gained in the course of research work as well as the results of comparative studies and their agreement. Crystals of transparent fluorite and quartz served as comparative material. In the fluorites examined gaseous, liquid, and mixed - liquid-gaseous and gaseous-liquid - have been distinguished. The inclusions are represented by primary, two systems of primary-secondary, and secondary inclusions. The homogenization temperature of the inclusions in fluorites is shown on fig. 6 and tab. 1. Powder samples from the same specimens have been examined in the decrepimeter and the grain size of 0.30-0.75 mm has been found to be the most suitable for the examinations. Examples of decrepigraphs for fluorite are presented on fig. 7. Several maxima close to the homogenization temperatures have been obtained and points marking the beginning of their rise are shown in tab. l. A comparison between the homogenization and decrepitation temperatures yielded favourable results, the biggest difference - about + 13°C being found in the case of primary inclusions where gaseous inclusions predominate. The fluorites examined were formed at temperatures of about 215°C and the maxima mark two generation stages at the temperatures of 170 and 140°C and an influx of epigene solutions at the temperature of 110°C. Similar comparative tests have been carried out for quartz. The samples were taken from pegmatitic druses in granites. The inclusions were clearly predominated by the gaseous type and those homogenizing according to I type were rather scarce. The homogenization temperature of primary inclusions falls within the 250-275°C range. Also two systems of primary-secondary inclusions have been distinguished, their homogenization temperature being 165-195°C and 120-140°C. The secondary inclusions are scarce and their homogenization temperature has been found to be 120-140°C. The decrepitation studies of the quartz samples yielded ambigous results (fig. 8), the maxima overlap each other, the intensity of pops often decreases, peaks are blurred. Interpreting the decrepigraphs irrespectively of homogenization several temperature ranges may be found - 90, 135, 175, 320 and 390°C - which may indicate the main crystallization phase to have occurred at a temperature of about 320°C. The lower maxima mark the regeneration and epigene stages. The origin of the 390°C anomaly is not clear. Similarly to the case of fluorites, the biggest differences in results obtained from homogenization and decrepitation tests on quartz exist in the case of primary inclusions. Among them gaseous inclusions predominate and this is the probable source of the inconsistencies mentioned above. The compressibility coefficient for gases exceed those far fluids and for this reason the internal pressure increases much slowlier. Thus a certain correlation resulting from pressure during crystallization should be added to the homogenization temperature values determined.

 


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