PETROGRAPHY OF GRANITE FROM THE BAN PANG AND BAN MAI TAKHIAN AREA, AMPHOE LI, CHANGWAT LUMPHUN
Panjasawatwong, B. Phajuy and K. Palopakorn
Department of Geological Sciences, Chiang Mai University, Chiang Mai 50202, Thailand
ABSTRACT

The granitic rocks present in this report are from the Ban Pang and Ban Mai Takhian area, Amphoe Li, Changwat Lumphun that are considered to be part of eastern Li granite. They comprise variably textured silicified granitic rocks and monzogranites. The silicified granitic rocks show hiatal, megacrystic and fine-graned equigranular textures. The groundmass of the inequigranular varietics is texturally similar to the fine-grained equigranular rocks. Abundant anhedral quartz, crystals, either as isolated grains or as clusters devoid of conscrtal appearance, are the dominant features of the silicified granitic rocks. The monzogranites have medium-grained scriate and equigranular textures. Their quartz crystals are typically almost anhedral, and form clusters with consertal relationship. Both the granitic types have principal constituents, i.e. quartz, alkali feldspar (orthoclase and microcline) and plagioclase, typical of monzogranites but for one sample which is compositionally syenogranite. Biotite occurs as a subordinate constituent to the principal minerals. Minor and trace constituents are zircon/monazite, apatite and opaque mineral, and may include andalusite, cordierite, orthopyroxene, muscovite and tourmaline. The accessory mineral assemblage reveals that the studied granitic rocks are peraluminous granite (S-type), and that the granitic magna might have emplaced and solidified at pressures less than 0.6 kb (ca. 2 km). Almost all the silicified granitic rocks might have been derived from monzogranites by a silicification process.
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