HR: 0800h
AN: V41D-0823    [Abstracts]
TI: Late Cretaceous volcanic activity in the Korean Peninsula
AU: * Yun, S
EM: yunsh@pusan.ac.kr
AF: Pusan National University, Jangjeon-dong Geumjeong-gu, Busan, 609-735, Korea, Republic of
AU: Koh, J
EM: jskoh812@pusan.ac.kr
AB: Southern part of the Korean peninsula was one of the largest Cretaceous volcanic fields in the northwest Pacific. Volcanic activity began with the eruption of silicic and minor basaltic volcanic rocks which were intercalated into sedimentary rocks of the Sindong Group and the Hayang Group. After this minor activity, large volumes of volcanic rocks were erupted and the resultant Yucheon Group consists mainly of volcanic deposits. Volcanic activity in the Gyeongsang Basin can be divided into four main stages; (1) early minor silicic and alkali-basaltic volcanism, (2) the Chaeyaksan alkali-basalt volcanism, (3) the Jusasan andesitic volcanism, and (4) the Unmunsa rhyolitic volcanism. Cretaceous volcanic rocks outside the Gyeongsang Basin are associated with volcano-sedimentary pull-apart basins or troughs which developed along a series of NE-trending sinistral strike-slip faults. The Cretaceous volcanic rocks distributed both in and outside the Gyeongsang Basin are composed of basalt, basaltic andesite, andesite, dacite and rhyolite. Their geochemical trends show successive differentiation processes of B-A-R associations. The volcanic rocks gradually changed in composition from alkalic in the early stages through alkalic/calc-alkalic in the middle stages to calc-alkalic in late stages, and the volcanic activity became more explosive with time. The trace element composition and REE patterns of the volcanis rocks, which are characterized by a high LILE/HFSE ratio and enrichment in LREE, suggest that they are typical of Andean-type continental margin-arc calc-alkaline volcanic rocks produced in a subduction environment. The initial 87Sr/86Sr ratios of volcanic rocks from the Gyeongsang Basin were progressively lowered with time from 0.7061 to 0.7049. The whole rock chemistry and Sr isotopic composition of the Jusasan and Unmunsa volcanis rocks suggest that the basaltic andesite/andesite evolved mainly by fractional crystallization from basaltic primary magma which produced by partial melting of the mantle wedge. Dacite/rhyolite magma was mostly produced by fractional crystallization including plagioclase feldspar but it might have partly undergone crustal assimilation during the fractionation in a high level magma chamber.
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting