Available online at www.sciencedirect.com
Tectonophysics 455 (2008) 106 – 108
www.elsevier.com/locate/tecto
Correspondence
Reply to comments by H. Mashima on ‘Evolution of the eastern margin of
Korea: constraints on the opening of the East Sea (Japan Sea)’ by Kim et al.
[Tectonophysics 436 (2007) 37–55]
Han-Joon Kim a,⁎, Gwang Hoon Lee b , Hyeong-Tae Jou a
a
Marine Environment & Characteristics, Korea Ocean R & D Institute, Ansan P.O. Box 29, 425-600, Korea
b
Dept. of Environmental Exploration Engineering, Pukyong National University, Busan 608-737, Korea
Received 12 December 2007; accepted 12 December 2007
Available online 27 December 2007
Abstract
We thank H. Mashima for his interest in our recent article in Tectonophysics [Kim, H.J., Lee, G.H., Jou, H.T., Cho, H.M., Yoo, H.S., Park, G.T.,
Kim, J.S., 2007, Evolution of the eastern margin of Korea: Constraints on the opening of the East Sea (Japan Sea). Tectonophysics 436, 37–55.] and
welcome the opportunity to respond to his comments. In our article we suggested that the southern part of the East Sea (Japan Sea) opened principally
in the southeast direction in response to the northwestward subduction of the Pacific Plate beneath the Japan Arc. In contrast, Mashima claims that the
opening of the East Sea was achieved in the south–southeast direction. However, there are many crucial things in his comments that we find
scientifically unconvincing and misleading. In this reply, we give a detailed response to his comments.
© 2007 Elsevier B.V. All rights reserved.
Keywords: East Sea; Korean margin; Separation of SW Japan; Yamato Bank; Korea Plateau
1. Separation direction of the Yamato Bank and the Korea
Plateau
There are a number of submerged structural highs in the East
Sea such as the Yamato Bank (see Fig. 1 of Kim et al., 2007); they
are interpreted as continental fragments separated from the
Eurasian continental margin to their present locations while the
East Sea opened. Mashima suggests from the topography of the
East Sea that the southern slope of the Tartar Strait fits well with
the northern slope of the Yamato Bank. Therefore, he infers that
the Yamato Bank migrated south–southwestward. However, the
topography of the East Sea indicates that it is more likely that the
Yamato Basin migrated southeastward from the position suggested in Kim et al. (2007). Mashima should consider magnetic
anomalies in the eastern part of the Japan Basin. If the Yamato
Bank had migrated south–southwestward, as Mashima suggests,
the magnetic anomalies in the eastern part of the Japan Basin
should trend ESE (east–southeast), where oceanic crust is
⁎ Corresponding author. Tel.: +82 31 400 6275; fax: +82 31 408 5822.
E-mail address: [email protected] (H.-J. Kim).
0040-1951/$ - see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.tecto.2007.12.010
emplaced. However, the identified magnetic anomalies in this
region strike N70°E, which implies that seafloor spreading took
place toward the SSE and consequently defies Mashima's
suggestion. Essentially, Mashima's suggestion is a citation of
the kinematics implicated in the pull-apart opening models of the
East Sea (e.g., Jolivet et al., 1994; Lallemand and Jolivet, 1985).
Even in these models, it is suggested that the Yamato Bank
migrated from the location depicted in Kim et al. (2007). The
wedge-shaped distribution of the oceanic crust in the Japan Basin
(see Fig. 11 of Tamaki et al., 1992), which further suggests a large
displacement in the northeastern Japan Basin and much smaller
displacement in the western Japan Basin, is also not compatible
with the model by Mashima in which the western and eastern
corners of the Yamato Bank have moved almost the same distance.
Mashima additionally suggests that the Korea Plateau migrated
in the same SSW (south–southwest) direction as the Yamato Bank.
If this had happened, the Korea Plateau would have impinged on
the Korean Peninsula and the eastern Korean margin adjacent to
the Korea Plateau should show evidence of extensive contractile
tectonism. However, no structural features suggesting contraction
are known in the eastern margin of Korea immediately west of the
Correspondence
107
Korea Plateau, as shown by multichannel seismic profiles and
explained in detail in Kim et al. (2007); what we see there is
extension with no or negligible contraction. Furthermore, rocks
dredged from the Korea Plateau are closely tied to the adjacent
Korean Peninsula in composition (Ryu and Han, 1996).
2. Separation of the southwestern Japan Arc and opening
of the Ulleung Basin
Mashima argues that the northwestward increase of water
depth and sediment thickness in the Ulleung Basin (Tsushima
Basin) is not compatible with the NE–SW extension axis of
Kim et al. (2007). We are not quite sure how water depth and
sediment thickness have anything to do with the orientation of
the extension axis in the Ulleung Basin where much of sediment
has been supplied from the south and southeast (Lee et al.,
2001). Mashima referred to Lee and Kim (2002) to bring up the
northwestward increase of sediment thickness but the seismic
profiles and sediment thickness maps in Lee et al. (2001, their
Figs. 4 and 9) and Lee and Kim (2002, their Fig. 3) clearly show
north- or northwestward ‘decrease’ of sediment thickness. The
total sediment thickness map by Lee et al. (2001, their Fig. 9)
also shows an ENE (east–northeast)-trending median high that
divides the basin into the northern basement low and the
southern depocenter. This median high may be a remnant axis of
extension and is probably compatible with the opening of the
Ulleung Basin toward the SSE (south–southeast).
Mashima evoked the pull-apart opening model of the East Sea
by Jolivet et al. (1994) to suggest that the SW Japan Arc
translated toward the SSW along some fault that outlines the
western boundary of the Ulleung Basin. However, even this
model suggests a significant amount of extension of the Ulleung
Basin in the SE direction and a certain amount of counterclockwise rotation of the SW Japan Arc while the SW Japan Arc
underwent south–southwestward translation along the fault
(Jolivet et al., 1994, their Fig. 11). In the frequently cited
opening models of the East Sea proposed by Otofuji (1996) and
Jolivet et al. (1994), the position of SW Japan before its
separation from near the Korean Peninsula was given without
strict geologic evidence. Recently, Otoh (2007) constrained the
position of SW Japan before the opening of the East Sea by
correlating land geology of Japan, Korea, and Russia Primorye.
The position of SW Japan in his study bears noticeable
resemblance to that suggested by Kim et al. (2007), implying
its counterclockwise rotation and separation toward the SE, as
inferred by Kim et al. (2007). If we incorporate the constrained
position of SW Japan, Fig. 12a in Kim et al. (2007) can be
modified as Fig. 1 that shows the positions of tectonic units
before the separation of the Japan Arc from the Korean Peninsula.
Some of the key comments by Mashima are essentially based
on the physiography of the East Sea. Bathymetric data
undoubtedly play a certain and important role in understanding
the regime and spatial configuration of stress with which to
interpret tectonic activity. However, they should be used as an
ancillary means because they do not provide useful information
so much as multichannel seismic reflection data particularly in
areas covered with thick sediments such as the continental
Fig. 1. Positions of tectonic units before the separation of the Japan Arc from the
Korean Peninsula. Note that this figure is a modification of Fig. 12a of Kim et al.
(2007) constrained by the study of Otoh (2007). NKP = North Korea Plateau and
YM = Yamato Bank.
margins of the East Sea, where the rift fabric is completely
concealed. Tectonic interpretation is quite more than geomorphology or physiography alone can afford.
Mashima also states that Kim et al. (2007) suggested the
opening direction of the Ulleung Basin is SE based on bathymetric and magnetic data. In fact, the interpretation in Kim et al.
(2007) was drawn from a well-documented set of multichannel
seismic reflection profiles in conjunction with magnetic and
bathymetric data. Although models for the opening of the East
Sea have been put forward prolifically (e.g., Otofuji, 1996;
Jolivet et al., 1994), they have not addressed the tectonic
evolution of the continental margins where the early history of
rifting to spreading processes was registered. The multichannel
seismic reflection data set used in Kim et al. (2007) is adequate to
interpret these processes leading to the separation of the SW
Japan Arc from the eastern Korean margin.
3. Tushima-Goto fault as a master fault for pull-apart
opening of the Ulleung Basin
Mashima suggests that there is a fault in the western Ulleung
Basin and this fault is an extension of the Tsushima-Goto fault
that would have guided a right-lateral displacement leading to
the pull-apart opening of the Ulleung Basin. It seems that the
assumed position of the Tsushima-Goto fault coincides with the
locus of breakup at the base of the continental slope suggested by
Kim et al. (2007). Mashima's suggestion is another citation of
the kinematics explained in the pull-apart opening model by
Jolivet et al. (1994) and Yoon and Chough (1995). The pull-apart
opening model explains many structural deformations in the
Japan Arc and on its continental margin. However, data in Kim
et al. (2007) do not provide any evidence of strike–slip tectonics
as the main mechanism responsible for the deformation at the
108
Correspondence
eastern Korean margin. Detailed descriptions and reasoning are
given in Kim et al. (2007). Drawing an extension of the
Tsushima-Goto fault along the western boundary of the Ulleung
Basin and assuming it as a master strike–slip fault to guide the
south–southwestward translation of the SW Japan Arc is just
self-fulfillment unless it is substantiated by scientific evidence.
Acknowledgement
This work was supported by the Korea Ocean Research and
Development Institute under grant PE97605.
References
Jolivet, L., Tamaki, K., Fournier, M., 1994. Japan Sea, opening history and
mechanism: a synthesis. Journal of Geophysical Research. 99, 22,237–22,259.
Kim, H.J., Lee, G.H., Jou, H.T., Cho, H.M., Yoo, H.S., Park, G.T., Kim, J.S.,
2007. Evolution of the eastern margin of Korea: constraints on the opening
of the East Sea (Japan Sea). Tectonophysics 436, 37–55.
Lallemand, S., Jolivet, L., 1985. Japan Sea: a pull-apart basin? Earth and
Planetary Science Letters 76, 375–389.
Lee, G.H., Kim, H.J., Han, S.J., Kim, D.C., 2001. Seismic stratigraphy of the
deep Ulleung Basin in the East Sea (Japan Sea) back-arc basin. Marine and
Petroleum Geology 18, 615–634.
Lee, G.H., Kim, B., 2002. Infill history of the Ulleung Basin, East Sea (Sea of
Japan) and implications on source rocks and hydrocarbons. Marine and
Petroleum Geology 19, 829–845.
Otofuji, Y., 1996. Large tectonic movement of the Japan Arc in late Cenozoic
times inferred from paleomagnetism. Island Arc 5, 229–249.
Otoh, S., 2007. Geologic continuation between Japan and Korea before the
opening of Japan Sea. Presented at the International Workshop for Seismic
Investigation along Arc-Backarc basin-Continent Transect held at the Ocean
Research Institute, Tokyo Univ., June 14–15, 2007.
Ryu, J.M., Han, C.S., 1996. Marine geology–stratigraphy. In: Paek, R.J., et al.
(Ed.), Geology of Korea. The Institute of Geology, State Academy of Sciences,
DPR of Korea, pp. 391–408.
Tamaki, K., Suyehiro, K., Allan, J., Ingle, J.C., Pisciotto, A., 1992. Tectonic
synthesis and implications of Japan Sea ODP Drilling. Proceedings of the
Ocean Drilling Program 127/128, 1333–1348.
Yoon, S.H., Chough, S.K., 1995. Regional strike slip in the eastern continental
margin of Korea and its tectonic implications for the evolution of Ulleung Basin,
East Sea (Sea of Japan). Geological Society of American Bulletin 107, 83–97.