寶城-順天 地域에 分布하는 正片麻岩類의 地質時代와 成因에 對한 硏究

Geochronology and petrogenesis on orthogneiss in the Bosung-Suncheon area

Orthogneiss of the study area is meta-igneous complex that composed of granite gneiss, porphyroblastic gneiss and migmatitic gneiss. Migmatitic gneiss produced from granite gneiss and porphyroblastic gneiss by strong ductile shearing. These rocks show mostly gneissic and partly mortar textures by strong regional metamorphism and ductile shearing during several orogenies. ⁴⁰Ar-³⁹Ar incremental-release ages of these rocks have been determined for 1 hornblende, 1 biotite and 3 muscovite concentrates separated from orthogneisses in this area. Ages of regional metamorphism and ductile shearing of these rocks are more than 5 stages(1500 Ma, 260 Ma, 190 Ma, 180-170 Ma and 160 Ma) under 300℃ to 500℃. These rocks had not been nearly effected by Daebo orogeny, because this area is far from Daebo granite bodies. The general trend of major chemical composition and mineral composition of these orthogneisses suggest that these rocks are some series of differentiated products from magma.