HR: 1340h
AN: V43A-1551    [Abstracts]
TI: U-Pb Zircon Geochronology of Early Jurassic Daedong Supergroup, South Korea: Tectonic implications
AU: * Jeon, H
EM: allyjin0@snu.ac.kr
AF: School of Earth and Environmental Sci., Seoul Nat­_l Univ., Seoul, 151-747 Korea, Republic of
AU: Cho, M
EM: moonsup@snu.ac.kr
AF: School of Earth and Environmental Sci., Seoul Nat­_l Univ., Seoul, 151-747 Korea, Republic of
AU: Kim, H
V43A-1551 AF: School of Earth and Environmental Sci., Seoul Nat­_l Univ., Seoul, 151-747 Korea, Republic of
AU: Horie, K
V43A-1551 AF: Dept. Earth and Planetary Sci., Hiroshima Univ., Hiroshima, 739-8526 Japan
AU: Hidaka, H
V43A-1551 AF: Dept. Earth and Planetary Sci., Hiroshima Univ., Hiroshima, 739-8526 Japan
AB: The ultrahigh-pressure collisional belt between the North China Block (NCB) and South China Block (SCB) may extend to Korean Peninsula, as suggested by a recent finding of eclogitic rocks. Previous paleomagnetic studies also suggest that the Bansong and Nampo groups, two representatives of the Daedong Supergroup, belong to the NCB and SCB, respectively. The Daedong Supergroup is known to comprise Late Triassic-Early Jurassic lacustrine sedimentary rocks. In the absence of absolute age constraints, this supergroup is often thought to be a product of exhumation related to the Triassic collisional orogeny. We analyzed zircon grains from seven samples using the SHRIMP, in order to (1) constrain the age of sedimentation, (2) determine the ages of detrital zricons, and (3) provide new perspectives on the evolution of Triassic collision. Zircons from two samples of syn-depositional tuff in the Bansong Group yield a weighted-mean 206Pb/238U age of 197+/-11 Ma (n=11) and 203+/-10 Ma (n=14), respectively. In addition, young detrital zircons from a sandstone gives similar age of 198+/-9 Ma (n=9). It is thus likely that the Bansong Group was deposited during the Earliest Jurassic. On the other hand, in the Nampo Group, volcanic tuff is absent, and relatively young grains from a sandstone give an age of 221+/-7 Ma (n=8). Thus, we interpret that both groups containing same plant fossils were deposited simultaneously at ca. 200 Ma after the Triassic continental collision. U-Pb ages of detrital zircons are divided into four major age components: (1) Early-Middle Archean (3.64-2.97 Ga), (2) Late Archean-Early Proterozoic with a maximum age frequency between 2.63 and 2.33 Ga, (3) late Early Proterozoic (1.98-1.75 Ga), (4) Triassic-Early Jurassic (240-190 Ma). Although the relative proportion of each component is slightly variable among the analyzed samples, the age distributions are apparently similar between the Bansong and Nampo groups. In particular, the presence of Early-Middle Archean grains in both groups is indicative of provenances belonging to North China Block. Taken together, we suggest that Bansong and Nampo groups of the Daedong Supergroup belong to the same block in contrast to the claim based on paleomagnetic data.
DE: 1708 Geochronology
DE: 8169 Sedimentary basin processes
DE: 9320 Asia
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005