Petrography and Geochemistry of Granitic Rocks at Silapetch Waterfall, Pua District, Nan Province, Northern Thailand
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Abstract
Petrography of the granitic rocks at Silapect waterfall and nearby area shows plagioclase, quartz, biotite and hornblende that are major minerals composition. Minor minerals composition contains; K-feldspar, chlorite, apatite, epidote and opaque minerals. Modal analysis on the rock slabs and thin-sections were applied to medium to coarse grained granitic specimen, while only classical point counting in thin-sections was applied fine to medium grained granitic specimen. The results show that this study area can be divided into two categories, namely, granodiorite and monzodiorite. Granodiorite rocks were observed as outcrops, which show equigranular and primary texture with medium to coarse grain. The loose blocks of monzodiorite present same texture as granodiorite but there are difference in grain size (fine to medium grain). Geochemically, the granitic rock in the study area have an extended composition range, high values of Na2O moreover 3.2%, values of Al2O3/(Na2O+K2O+CaO) content drop off 1.1% and CIPW norm of corrundum less than 1%.The study area can be classified as I-type granites which is clearly a part of the Eastern Granitiod Belt.
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Copyright © 2008 Department of Geology, Faculty of Science, Chulalongkorn University. Parts of an article can be photocopied or reproduced without prior written permission from the author(s), but due acknowledgments should be stated or cited accordingly.
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