Petrogenesis and Metamorphism of Charnockite of Eastern Jirisan Area

Precambrian metamorphic rocks of southwest Sobaeksan massif consist of mainly granitic gneiss, porphyroblastic gneiss and quartzofeldspathic gneiss. The orthopyroxene-bearing rocks(charnockites) are found in the west of Hadong-Sancheong anorthosite complex. The charnockites are 3km wide, 12km long and divided into massive and foliated types based on their texture. The compositions of charnockites are comparable to granodiorite to adamellite and subalkaline. Variations in major and trace elemental abundances show typical magmatic differentiation trends. The geochemical data plotted on tectonic discrimination diagrams reveal that these charnockites were formed in the active tectonic environment. The massive and folidated charnockites are mainly composed of plagioclase, orthopyroxene, microcline, quartz and disseminated garnet. Garnets generally show characteristic zonal textures with decreasing Xalm(0.74~ 0.83), Xpy(0.07~0.12) and XMg(0.12~0.08) and increasing Xgrs(0.03~0.15) from core to rim. Metamorphic temperature and pressure of the charnockites estimated from orthopyroxene-garnet-plagioclase-quartz assemblages show wide range of variation of 600~900 o C and 2.5~7.5 kbar respectively. The results of P- T estimates indicate an anticlockwise P-T evolution path.