2001 Volume 40 Issue 3 Pages 185-196
The climate conditions in Sri Lanaka are briefly divided into three zones (wet, dry and intermediate), based on the average annual rainfall. Three typical weathered charnokite outcropswere selected in each zone.
Weathering products formed from charnockitic rock distributed in three different climate were investigated by means of X-ray diffraction, Differential thermal analysis (DTA), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and X-ray fluorescence analysis.
In wet zone, vermiculite and kaolin mineral accompanied with gibbsite and goethite were formed. Vermiculite, interstratified mineral of biotite and vermiculite, smectite, halloysite and kaolinite were occurred in the outcrop of dry zone. On the other hand, only kaolinite and halloysite were formed in the intermediate zone. According to these results, the sequences of the formation of clay minerals in each zone are as follows;
Wet zone: vermiculite → kaolinite → gibbsite.
Halloysite →
Intermediate zone: halloysite → kaolinite.
Dry zone: biotite/vermiculite → vermiculite
Smectite → kaolinite
Halloysite →
Based on the chemical analysis, a clearly different alteration trend in the dry zone compared with the wet and intermediate zones is recognized. The Chemical Intensity of Alteration ofthe most weatheredparts of charnokitic rocks in the wet, intermediate and dry zones indicates 100, 98 and less than 70, respectively.
According to these results, alteration pathways from fresh to weathered charnokaitic rocks are clearly different under each climate conditions.
