• Ocean and Polar Research
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• v.24 no.3
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• pp.197-205
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• 2002

Total magnetic field and high-resolution bathymetric data were collected over nine seamounts to the northwest of the Marshall Islands in the western Pacific. Magnetic parameters including inclination and declination were calculated from the magnetic anomalies using inversion algorithm of Plouff (1976), and a corresponding paleomagnetic pole was determined with the magnetic parameters. The paleomagnetic poles determined in this study were compared with the previous apparent polar wander path (APWP) of Pacific plate. Most seamounts of the study area have normal polarity. The study reveals that all nine seamounts in the study area formed in the southern hemisphere during the Cretaceous based on their comparison with the APWP of Pacific plate. The ages estimated from paleomagnetic poles can be divided by age into three groups: the oldest (OSM1 and OSM3), middle age (OSM2, OSM4, and 6-2), and the youngest (OSM5-1, 5-2, 5-3, and 6-1). The fermer two groups and the latter seem to be coincident with two distinct pulses of Cretaceous volcanic activity (115-90 Ma and 83-65 Ma). As a whole the seamounts at southwest of the study area are older than at those northeast.

• Economic and Environmental Geology
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• v.26 no.3
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• pp.383-393
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• 1993

Paleomagnetic data have been obtained from the Lower Triassic Tonggo formation which is exposed in the E-W trending Baekunsan syncline comprising the Pyongan Supergroup in eastern Korea. Two ancient components of magnetization are recovered in this formation by detailed thermal demagnetization: a post-folding component and a pre-folding component The post-folding component ($D/I=58.8/55.5^{\circ}$) is normally magnetized and appears to acquire in the Cretaceous Normal Superchron. It is a magnetic signature of the Daebo Orogeny and has been rotated clockwise since this magnetization has been acquired, in common with the main synclinal axis. The pre-folding component ($D/I=1.1/19.4^{\circ}$, Paleopole at $306.1^{\circ}E$, $63.2^{\circ}N$) passes fold and reversal tests and is inferred to be a post-depositional or early chemical diagenetic remanence of Lower-Middle Triassic age. This paleopole corresponds only with the Lower Triassic poles from the North China Block: it is removed from the contemporary poles from the South China Block. If the result of this study is corrected for the clockwise rotation deduced from the Cretaceous overprint, the enhanced agreement with the Lower Triassic poles from the North China block can be achieved. Therefore, a first order correlation between the Korean Peninsula and North China at least since Lower Triassic times is identified in this study.

• 한국지구물리탐사학회:학술대회논문집
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• 2007.06a
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• pp.337-342
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• 2007

The representative Cretaceous-Tertiary paleomagnetic poles of the Korean Peninsula have been obtained from primary remanences of unremagnetized rocks: $59.6^{\circ}N$, $194.7^{\circ}E$ for $K_{1M}$; $67.6^{\circ}N$, $207.7^{\circ}E$ for $K_{1L}$; $71.1^{\circ}N$, $215.2^{\circ}E$ for $K_2$; and $84.9^{\circ}N$, $292.6^{\circ}E$ for the Miocene. Chemical remanences of remagnetized rocks also yield Early Tertiary paleomagnetic pole ($83.9^{\circ}N$, $88.3^{\circ}E$). These paleopoles provide the tentative APWP of the Korean Peninsula since the Cretaceous, and suggest some tectonic interpretations as follows. The Korean Peninsula was located at similar latitude to the present position, and rotated clockwise with respect to the adjacent blocks during the Cretaceous. The Korean Peninsula experienced latitudinal movement during the Early Tertiary, which was possibly associated with the continental collision between India and Asia. The Korean Peninsula and Southwest Japan might be independent terrains during the Cretaceous based on the temporal discrepancies of the southward movements and the clockwise rotations of the two blocks with respect to Eurasia.

• Economic and Environmental Geology
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• v.28 no.6
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• pp.559-569
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• 1995

Paleomagnetic data have been obtained from the Upper Carboniferous-Permian Komok and Cheolam Groups which are exposed in the E-W trending Baekunsan syncline comprising the Pyongan Supergroup in eastern Korea. Two ancient components of magnetization are recovered in these groups by detailed thermal demagnetization: a post-folding component and a pre-folding component. The post-folding component $(D/I=54.0/54.6^{\circ},\;{\alpha}_{95}=14.6^{\circ})$ is a magnetic signature of the Oaebo Orogeny and appears to have been confined mainly to Cretaceous Normal Superchron. It has been rotated clockwise since this magnetization has been acquired. The pre-folding components ($D/I=341/-9.2^{\circ},\;{\alpha}_{95}=7.2^{\circ})$, paleopole at $335.7^{\circ}E$, $44.6^{\circ}N$ for Upper Carboniferous; $D/I=358.3/11.5^{\circ},\;{\alpha}_{95}=6.3^{\circ})$, paleopole at $311.9^{\circ}E$, $58.7^{\circ}N$ for Permian) pass fold and reversal tests. These paleopoles correspond only with the contemporaneous poles from the North China Block: they are removed from the poles from the South China Block. If the results of this study are corrected for the clockwise rotation deduced from the prefolding component, the enhanced agreement with North China Block can be achieved. Therefore, a first-order correlation between the Korean Peninsula and North China at least since Upper Paleozoic times is identified in this study.

• Economic and Environmental Geology
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• v.40 no.2 s.183
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• pp.191-207
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• 2007

A paleomagnetic investigation for the Cretaceous rocks in the Buyeo and Hampyeong Basins, located out of the Gyeongsang Basin, was carried out in order to elucidate the paleomagnetic directions in conjunction with the formation of the basins. Typical stepwise thermal demagnetization and measurement methods were used to determine the directions of characteristic remanent magnetizations (ChRMs). The mean direction of the sedimentary rocks from the Buyeo Basin after bedding correction $(D/I=356.5^{\circ}/61.5^{\circ},\;k=39.3\;\alpha_{95}=7.4^{\circ})$, is more dispersed than that before bedding correction $(D/I=356.5^{\circ}/61.5^{\circ},\;k=39.3\;\alpha_{95}=7.4^{\circ})$, which suggests that the rocks in the Buyeo Basin were remagnetized. However, the statistics and dispersion of the ChRM directions after bedding correction are still acceptable and the paleomagnetic pole position after tilt correction $(Lat./Long.=69.3^{\circ}N/186.7^{\circ}E,\;K=11.6\;A_{95}=14.0^{\circ})$ is closer to that of the Late Cretaceous pole of the Korean Peninsula. More detailed study is needed to confirm the nature of the remagnetization in the Buyeo Basin. On the other hand, the paleomagnetic pole before bedding correction $(Lat./Long.=81.6^{\circ}N/106.9^{\circ}E,\;K=25.1\;A_{95}=9.3^{\circ})$ is positioned near the paleogene pole of the Eurasian APWP. The mean ChRM direction of the sedimentary rocks from the Hampyeong Basin after bedding correction is $D/I=32.5^{\circ}/55.4^{\circ},\;(k=35.6,\;\alpha_{95}=8.7^{\circ})$. It is more clustered than that before bedding correction $D/I=18.3^{\circ}/62.5^{\circ},\;k=14.1,\;\alpha_{95}=14.2^{\circ})$, indicating that the ChRM was acquired before tilting of the strata. The paleomagnetic pole position of the Cretaceous sedimentary rocks in the Hampyeong Basin, averaged out of site pole positions calculated from the tilt-corrected ChRMs, is $Lat./Long.=63.9^{\circ}N/202.7^{\circ}E,\;(K=21.3,\;A_{95}=7.6^{\circ})$, similar to the Late Cretaceous paleomagnetic pole of the Korean Peninsula $(Lat./Long.=70.9^{\circ}N/215.4^{\circ}E,\;A_{95}=5.3^{\circ})$, suggesting that the Hampyeong Basin has been stable since the Late Cretaceous period. One normal and two reversed ChRM directions are revealed through the measurements of the volcanic rocks from the Hampyeong Basin. Although these normal and reversed directions are not exactly antipodal, it is interpreted that the normal direction is the representative primary direction of the volcanic rocks of the Hampyeong Basin and the mixed polarity is the records of geomagnetic field at the time of the formation of the volcanic rocks. Paleomagnetic poles are at $Lat./Long.=70.2^{\circ}N/199.5^{\circ}E,\;(K=18.1,\;A_{95}=9.6^{\circ})$ for the normal direction, and $Lat./Long.=65.5^{\circ}S/251.3^{\circ}E,\;(K=7.1,\;A_{95}=20.7^{\circ})$ for the reversed direction. Compared with the representative pole positions of the Cretaceous period of the Korean Peninsula, it is concluded that the age of the volcanic rocks in the Hampyeong Basin is of the Late Cretaceous.

• Economic and Environmental Geology
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• v.37 no.2
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• pp.195-206
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• 2004

Paleomagnetic and rock-magnetic investigations have been carried out for the Cretaceous sedimentary rocks in the Poongam (also called Gapcheon) Basin in the eastern South Korea. A total of 128 independently oriented core samples were drilled from 13 sites for this study. The mean direction after bedding correction (D/I=353.1$^{\circ}$/55.6$^{\circ}$, k=21.5, =$$\alpha$_{95}$=10.1$^{\circ}$) is more dispersed than the mean direction before bedding correction (D/I=10.5$^{\circ}$/56.9$^{\circ}$, k=73.9, =$$\alpha$_{95}$=5.3$^{\circ}$), and the stepwise unfolding of the characteristic remanent magnetization (ChRM) reveals a maximum value of k at 20% unfolding. Secondary authigenic hematite accompanied by altered clays such as chlorite was identified by the electron microscope observations. These results collectively imply that the ChRM is remagnetized due to the formation of the secondary authigenic hematite after tilting of the strata. It is interpreted that the chemical remagnetization was connected to the introduction of mixed magmatic-meteoric fluids, which formed hydrothermal vein deposits near the study area. The paleomagnetic pole position (214.3$^{\circ}$E, 81.6$^{\circ}$N, =$A_{95}$=7.4$^{\circ}$) of the Cretaceous sedimentary rocks calculated from remagnetized directions is close to those of the Late Cretaceous and Tertiary poles of the Korean Peninsula. This Late Cretaceous to Tertiary remagnetization seems to be widespread over the Okcheon Belt because the chemical remagnetization is previously reported to be found in rocks from other Cretaceous small basins (e.g., Eumseong, Gongju and Youngdong basins) along the Okcheon Belt and some Paleozoic strata from the Okcheon unmetamorphosed zone.