Petrography and geochemistry of intrusive rocks at Ban Pho-Sawan area, Amphoe Bung Samphan, Changwat Phetchabun

Abstract

The main objective of thesis is to find out a relationship among intrusive rocks occur in Ban Phosawan area, Amphoe Bung Samphan, Phetchabun province that show several field-notable feathers. The study area cover approximately 176 km² and occupy in a position of the so-called "Eastern granite belt" of Thailand. It contains both extrusive and intrusive rocks. Based on petrography, whole-rock chemistry and mineral chemistry, intrusive rocks in study area can be divided into four types namely gabbro, diorite, quartz diorite and hornblende-biotite ganodiorite, with a composition ranging from mafic to felsic respectively. Most of them are l-type affinity and calc-alkaline series. Their trace element characteristics suggest that most of them emplaced in a setting of volcanic arc and their whole-rock compositions may affected by clinopyroxene and plagioclase fractionation. Rare earth spider diagram patterns suggest that most of them originated from the same magma source. The Al-in-hornblende barometry and amphibole-plagioclase thermometry reveal that The most probable ranges of pressure and temperature for those four intrusive rocks are 2.5 to 2.8 kbar, and 609 to 671 °c, respectively. The U-Pb age from two in situ zircon grains dated by laser ablation - ICP MS technique yield 230 ± 4 Ma, middle Triassic period. Based on all results above, the four rock types seems to relate to one another as a ‘zoned pluton’ which emplace as a unique mass of magma, consequently, in situ differentiation was took place in the kind of side-wall accretion or inward crystal fractionation.