UPPER MESOZOIC UNCONFORMITY-BOUNDED UNITS OF KOREAN PENINSULA WITHIN KOGURYO MAGMATIC PROVINCE

Abstract

The Upper Mesozoic strate of the Korean Peninsula are subdivisible into three unconformity-bounded units, and they developed time-transgressively toward the Pacific. The lower unit straddling the Jurassic-Cretaceous boundary occurs profusely in Northern Korea with substantial amount of volcanic rocks but is extremely rare in Southern Korea. The middle, Hauterivian-lower Albian, unit occurs scattered in the Korean Peninsula but preponderantly in the Kyongsang Basin, Southeastern Korea. The upper unit is extremely rare in North Korea but is abundant in the southern part of Southern Korea, where it is characterized by calcalkaline volcanic rocks. Such a tendency of southeastward younging is also apparent over the ‘Koguryo Magmatic Province’ inclusive of Korea, suggesting that the shifting was caused by the retreating subduction zone on the Pacific side. But the post-Triassic magmatisms were largely keeping the same overall area suggesting a sustained hot spot above a plume below. The association in space and time of magmatisms and sedimentations implies their genetic relation. The Cretaceous sedimentary basins of Southern Korea are interpreted as pull-apart origins under a strike-slip tectonics.