潭陽―鎭安사이에 分布하는 葉理狀花崗岩類에 對한 地質時代와 成因에 關한 硏究

Geochronology and petrochemistry of foliated granites between Damyang and Jinan

Plutons of Damyang-Jinan area consist of gray feldspar granite gneiss, biotite granite gneiss, foliated granites, Namweon granites, gabbro, biotite granite and Ogangri granite in term of mineralogical, texture and field evidence. From Isotope data of study area, chronological order of the Plutons are the Pre-cambrian gray feldspar granite gneiss(Ar39-Ar40, hornblende, 1998.4±8.3Ma), middle to late Triassic Daegang foliated granite(Rb/Sr, whole rock, 228±4Ma), foliated hornblende biotite granodiorite(K/Ar, hornblende, 198.7±9.9.Ma), Sunchang foliated granodiorite(Rb/Sr, whole rock, 222±4Ma), foliated two mica granite, Samori foliated granite and Namweon granite(Rb/Sr, whole rock, 211±3Ma: K/Ar, hornblende, 203±10.2 Ma), middle Jurassic Gabbro(K/Ar, hornblende, 180.7±9MA) and biotite granite, and Cretaceous Ogangri granite. According to variations diagrams of Al₂O₃ versus normative Pl(100 An)/(Ab+An), Daegang foliated granite is plotted on tholeiitic series, and other foliated granites on calc alkaline rock series which are consider to be formed by magmatism at continental margin and island arc region. And alkalinity versus SiO₂ shows that Daegang folited granite and Samori foliated granite are correspond to alkaline region, foliated hornblende biotite granodiorite and Sunchang foliated granodiorite to calc alkaline region, and foliated two mica granite to both regions. According to ACF diagrams, Daegang and Samori foliated granites are plotted on S-type. Foliated hornblende biotite granodiorite and Sunchang foliated granodiorite on I-type, and foliated two mica granite on both type. Foliated granites are a series of differentiated products from cogenetic magma, and effected under ductile sheared zone. Characteristic foliation of foliated granites are considered to be generated by dextral strike slip faulting and ductile shearing.