경상분지 고성지역의 화성암류에 대한 암석학적 연구 II.미량원소 지구화학과 Rb-Sr방사성연대

he igneous rocks in the Goseonf area are composed of the volcanic rocks (andesitic lapilli tuff and rhyodacite), Rulgugsa granites (Hornblende-biotite granite and two pyroxene granite) and intrusive andesites. I the variation diagrams of the trace and rare earth element contents and elemental ratios as well as the REE patterns, the three igneous rock types show different variational trends and patterns. The geochemical features represent that the igneous rocks in the area were formed from three different magmatic pulses. Two independentlycarried out Rb-Sr isotope experiments for the Goseong granites show that the whole rock ages and Sr initial ratios of the granites are 66.4±6.2 Ma, 0.70517±22(2δ) and 71.3±6.8 Ma, 0.70506±18(2δ), respectively. These results suggest that the granites magma originated from the lower crustal materials of igneous origin intruded into the area during the late Cretaceous period. Ma-san hornblende-biotite granite emplaced at the vicinity of the Goseong area is very similar to the Goseong granite in its mineral compositions, major, trace and rare earth element contents and patterns. The intrudinf age (100 Ma) of the Ma-san granite is order than that of the Geseong granite, however. The similarity of the geochemical natures but the contrast of the intruding ages between the Masen and Goseong granites possibly indicate that the magma generation from the same source materials occurred at a temporal interval of ca. 30 Ma.