Evolution of the Dok Do seamounts,Ulleung Basin,East Sea: constraints based on the reconstruction of virtual geomagnetic poles using paleomagnetic data |
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Authors: | Chang Hwan Kim Chan Hong Park Eui Young Jeong Jong Sun Hwang Young Tak Ko |
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Institution: | (1) Dokdo Research Center, East Sea Research Institute, Korea Ocean Research & Development Institute, Uljin, 767-813, Korea;(2) East Sea Research Institute, Korea Ocean Research & Development Institute, Uljin, 767-813, Korea;(3) Petroleum and Marine Resources Research Division, Korea Institute of Geoscience & Mineral Resources, Daejeon, 305-350, Korea;(4) Deep-sea & Marine Georesources Research Department, Korea Ocean Research & Development Institute, Ansan, 425-600, Korea |
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Abstract: | In the Ulleung Basin, East Sea, the Dok Do seamount group comprises Dok Do (Dok Island), consisting of very small islets/rocks
and a large submerged volcanic edifice, and two voluminous tablemounts, Simheungtaek and Isabu. We attempted to reconstruct
the evolution of these seamounts, using virtual geomagnetic poles (VGPs) determined by the least-squares and the seminorm
magnetization methods, with 1,500 m upward continued magnetic anomalies. The VGPs of Dok Do with normal dipole anomaly, and
of Simheungtaek with normal dipole anomaly are located near the present magnetic pole. The VGP of Isabu with normal dipole
anomaly is located at low latitude, presumably due to overprints of reversals in the Tertiary, and the distortion of magnetization
and structures associated with volcanism after its formation. In contrast to the tablemounts, magnetic anomalies over Dok
Do are a combination of both normal polarity and reversed polarity dipoles in the northern hemisphere, indicating that Dok
Do has had at least two major eruptions, one during normal and another during reversed polarity intervals. From these results,
and information on the ages of the seamounts (either published radiometric ages of subaerial volcanic rocks, or ages reconstructed
in terms of reported elastic thickness incorporated into an existing cooling plate model), we tentatively propose that (1)
Isabu formed first, during a normal polarity interval after the opening of the East Sea had ceased; (2) this was followed
by an initial and subsequent large eruption of Dok Do during a normal polarity and a reversed polarity interval after about
5 Ma; and (3) the formation of Simheungtaek occurred in between that of Isabu and Dok Do in a normal polarity interval. The
pattern of normal/reversed magnetization is not inconsistent with the geomagnetic polarity timescale for at least the last
5 Ma. Nevertheless, precise ages of formation would need verification by additional geophysical/geochemical constraints. Evaluating
various possible models explaining the successive formation of the Dok Do seamounts, we currently favor fracturing and volcanism
related to compression-induced weakening of the extensional field from the late Miocene to Pliocene after the opening of the
East Sea. |
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