HR: 0800h
AN: T11C-1272    [Abstracts]
TI: Sr, Nd, Pb and Hf Isotopic Compositions of Late Cenozoic Alkali Basalts in South Korea: Evidence for Mixing Between the Two Dominant Asthenospheric Mantle Domains beneath East Asia
AU: * Choi, S
EM: sunghic@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109-1063 United States
AU: Mukasa, S B
EM: mukasa@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109-1063 United States
AU: Kwon, S
EM: kwanst@yonsei.ac.kr
AF: Yonsei University, Department of Earth System Sciences, Seoul, 120-749 Korea, Republic of
AU: Andronikov, A V
EM: andron@umich.edu
AF: University of Michigan, Department of Geological Sciences, Ann Arbor, MI 48109-1063 United States
AB: We determined the Sr, Nd, Pb and Hf isotopic compositions of late Cenozoic basaltic rocks from six lava-field provinces in South Korea, including Baengnyeong Island, Jogokni, Ganseong area, Jeju Island, Ulleung Island and Dog Island, in order to understand the nature of the mantle source. The basalts have OIB-like trace element abundance patterns, and also contain mantle-derived xenoliths. Available isotope data of late Cenozoic basalts from East Asia, along with ours, show that the mantle source has a DMM-EM1 array for northeast China and a DMM-EM2 array for Southeast Asia. We note that the basalts falling on an array between DMM and an intermediate end member between EM1 and EM2, are located between the two large-scale isotopic provinces, i.e., around the eastern part of South Korea. The most intriguing observation on the isotopic correlation diagrams is spatial variation from predominantly EM2 signatures in the basaltic lavas toward increasingly important addition of EM1, starting from Jeju Island to Ulleung and Dog Islands to Ganseong area, and to Baengnyeong Island. This is without any corresponding changes in the basement and the lithospheric mantle beneath the region. These observations suggest that the asthenospheric mantle source is dominant for the Cenozoic intraplate volcanism in East Asia, which is characterized by two distinct, large-scale domains. Previous studies on East Asian Cenozoic volcanic rocks have invoked origins by either plume activity or decompressional melting in a rift environment. On the basis of our new trace element and isotopic compositions which have OIB-like characteristics, we prefer a plume origin for these lavas. However, because tomographic images do not show distinct thermal anomaly that would be interpreted as a plume, we suggest that the magmatism might be the product of small, difficult to image multiple plumes that tapped the shallow part of the asthenosphere (probably the transition zone in the upper mantle).
DE: 8450 Planetary volcanism (5480)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8124 Earth's interior--composition and state (old 8105)
DE: 3640 Igneous petrology
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting