• The Journal of the Petrological Society of Korea
• /
• v.25 no.1
• /
• pp.51-67
• /
• 2016

Geochemical characteristics of the Early Cretaceous igneous rocks from eastern China and the Gyeongsang Basin, Korean Peninsula has been summarized. They have wide range of lithological variation with extrusive picrite-basalt-andesite-trachyte-rhyolite and lamprophyre, and intrusive gabbro-diorite-monzonite-syenite-granite and diabase in eastern China, mostly belonging to the high-K calc-alkaline or shoshonitic series. The volcanic rocks intercalated with the Hayang Group sedimentary assemblages in the Gyeongsang basin are high-K to shoshonitic basaltic trachyandesites. The Early Cretaceous basaltic rocks studied mostly fall within the field of within-plate basalts on the Zr/Y-Zr and Nb-Zr-Y tectonic discrimination diagrams. On a Sr-Nd isotope correlation diagram, basaltic rocks from the North China block (NCB) and the continent-continent collision zone (CZ) between the North and South China blocks plot into the enriched lower right quadrant along the extension of the mantle array. The initial $^{87}Sr/^{86}Sr$ ratios of basaltic rocks from the South China block (SCB) are indistinguishable from those of the NCB and CZ basaltic rocks, but their ${\varepsilon}_{Nd}$ (t) values are relatively more elevated, plotting in right side of the mantle array. Basaltic rocks from the NCB and CZ are characterized by low $^{206}Pb/^{204}Pb(t)$ ratios, lying to the left of the Geochron on the $^{207}Pb/^{204}Pb(t)$ vs. $^{206}Pb/^{204}Pb(t)$ correlation. Meanwhile, the SCB basaltic rocks have relatively radiogenic Pb isotopic compositions compared with those of the NCB and CZ basaltic rocks. Basaltic rocks from the Hayang Group plot within the field of the NCB basaltic rocks in Sr-Nd and Pb-Pb isotope spaces. Metasomatically enriched subcontinental lithospheric mantle (SCLM) is likely to have been the dominant source for the early Cretaceous magmatism. Asthenospheric upwelling under an early Cretaceous extensional tectonic setting in eastern China and the Korean Peninsula might be a heat source for melting of the enriched SCLM. Metasomatic agents proposed include partial melts of lower continental crust delaminated and foundered into the mantle or subducted Yangtze continental crust, or fluid/melt derived from the subducted paleo-Pacific plate.

• Economic and Environmental Geology
• /
• v.34 no.4
• /
• pp.355-373
• /
• 2001

Palaeomagnesim of Paleozoic Tuwibong Type Sequence in Yemi area was studied with a total of 256 core-samples collected from 23 sites. The study area (geographical coordinates: 37.l8$^{\circ}$N, l28.610E) is located between Taebaek and Yongwol belonging to the northeastern part of the Okchon Belt. Thermal cleaning was a most effective method to extract stable characteristic remanent magnetization (ChRM) direction, even though AF cleaning also worked on some specimens. Mean ChRM direction of the Cambrian Hwajol Formation was different from the present-day field direction and showed maximum clustering (max. k value) at 100% bedding-tilt correction. However, it could not pass the fold test. Ordovician Makkol and Kosong Limestones as well as Permian Sadong and Kobangsan Formations have very weak NRM, and were remagnetized into the present-day field direction. ChRM directions from the Carboniferous Hongjom Formation passed both fold and reversal tests. IRM experiments and blocking temperature spectrum indicate that both magnetite and haematite are carrier of the primary magnetization. Palaeomagnetic pole position from the Carboniferous Hongjom Formation is very similar to that of contemporary North China Block (NCB) suggesting that the study area was a part of, or located very near to, the NCB during Carboniferous.

• Proceedings of the KSEEG Conference
• /
• 2003.04a
• /
• pp.254-257
• /
• 2003

한반도에 대한 고지자기 연구는 유라시아 대륙의 지구조운동이 진행되었던 중생대 및 고생대암석에 대해 여러 사람들에 의해 활발히 수행되어왔다. 특히 1980년대 후반부터는 북중국지괴와 남중국지괴 사이의 충돌대인 친링-다비-수루 (Qinling-Dabie-Sulu) 조산대가 서해를 지나 한반도로 연장될 가능성에 대한 관심이 높아지고 있다. 한반도의 중부를 가로지르는 옥천대는 경기육괴와 영남육괴의 경제부로서 변성시기가 초기 Triassic으로 보고되고 있으며, 경기육괴 북부 휴전선 인접지역의 동서방향의 주향을 갖는 습곡-단층대인 임진강대는 남북 경계에 대한 정확한 정의는 성립되어있지는 않지만 Triassic에 광역변성작용을 받았다는 보고가 있으나, 이들 임진강대와 옥천대의 성인에 대한 논란은 현재에 이르기까지 계속되고 있다. (중략)

• The Journal of the Petrological Society of Korea
• /
• v.5 no.1
• /
• pp.89-107
• /
• 1996

Sr, Nd and Pb isotopic characteristics of alkaline lavas and tholeiites in Cheju Island show that the isotopic compositions of the former slightly overlap, but have relatively more depleted than the latter. However, in viewpoint of the two eruptional stratigraphies of tholeiites, the isotopic compositon of the older one is similar to those of alkaline rocks in Lava Plateau Stage after Lee (1982). These suggest that the parental magmas of alkaline lavas and tholeiites might have originated from the homogenous mantle sourve and that the characteristics of the mantle source to be partially melted might be different between the eruption stages. The isotopic signatures of the bolcanic rocks in Cheju Island overlap with those in Samoa Islands and South China Basin, indicating the DMM-EM IImixing trend. This is distingushed from the DMM-EM I trend of the Cenozoic volcanic rocks in Korea except for cheju Island and Northeastern China. The modelled binary mixing calculation between MM and EM IImaterials indicates that the mantle source of the volcanic rocks in Cheju Island has been mixed about less than 10% of enriched mantle material (EM II) with depleted mantle material (DMM). Concerned with the indentation model between North China Block (NCB) and South China Block (SCB) after Yin an Nie (1993), we suggest that the distinct isotopic features of DMM-EM I and DMM-EM IIof the Cenozoic volcanic rock in Korea as well as China can be explained by the difference of the nature of subcontinental lithospheric mantle as enriched mantle materials, i.e. EM I of NCB, while EM II of SCB.

• Economic and Environmental Geology
• /
• v.41 no.2
• /
• pp.173-181
• /
• 2008

CHIME ages were obtained from monazites in metamorphic rocks from the Seosan and Siheung Groups in the Gyeonggi gneiss complex, Korean peninsula. Monazite CHIME ages range from 234 to 257 Ma, corresponding to the late Permian to middle Triassic Songrim disturbance due to the collision event between the North and South China blocks within the Gyeonggi gneiss complex in the Korean peninsula. The CHIME ages are consistent with the metamorphic ages from the Hongseong area (231 Ma, Kim et al., 2006) and the Odesan area (245-248 Ma, Oh et al., 2006b) in the Gyeonggi gneiss complex and are older than those from the Dabie-Sulu collision belt (220${\sim}$242 Ma, Yang or of., 2003; Liu et al., 2003, 2004) suggesting that the collision between the North and South China blocks had occurred earlier in Korea than China.

• The Journal of the Petrological Society of Korea
• /
• v.14 no.3 s.41
• /
• pp.127-140
• /
• 2005

The Samyuri area of Jeoksang-myeon, Muju-gun at the Middle Yeongnam Massif consists of granitic gneiss, porphyroblastic gneiss and leucocratic gneiss, which correspond to Precambrian Wonnam Series. Here we discuss a geochemical implication of the data based on major element composition, trace element, rare earth element (REE), Sm-Nd and Rb-Sr isotope systematics of the boring cores in the granite gneiss area. The boring cores are granitic gneiss (including biotite gneiss) and amphibolite. The major and trace element compositions of granitic gneiss and amphibolite suggest that the protolith belongs to TTG (Tonalite-Trondhjemite-Granodiorite) and tholeiitic series, respectively. Chondrte-normalized REE patterns vary in LREE, HREE and Eu anomalies. The granitic gneiss and amphibolite have Sm-Nd whole rock age of $2,026{\pm}230(2{\sigma})$ Ma with an initial Nd isotopic ratio of $0.50979{\pm}0.00028(2{\sigma})$ (initial ${\epsilon}_{Nd}=-4.4$), which suggests that the source material was derived from old crustal material. Particularly, this initial ${\epsilon}$ Nd value belongs to the range of the geochemical evolution of Archean basement in North-China Craton, and also corresponds to the initial Nd isotope evolution line by Lee et al. (2005). In addition, chondrite-normalized REE pattern and initial Nd value of amphibolite are very similar to those of juvenile magma in crustal formation process.

• The Journal of the Petrological Society of Korea
• /
• v.20 no.4
• /
• pp.207-217
• /
• 2011

Here we report major element composition, trace and rare earth element abundance, Sm-Nd and Rb-Sr isotopic composition from Deokgu leucogranite. Chondrite-normalized REE pattern and its Eu anomaly are divided into 3 types systematically, and have close relationship with $SiO_2$ contents. Such geochemical characteristic indicates that the leucogranite was derived by feldspar fractionation from a common source magma. Sm-Nd and Rb-Sr whole rock ages are $1,785{\pm}180Ma$ (initial $^{143}Nd/^{144}Nd\;ratio=0.51003{\pm}0.00016,\;2{\sigma}$; ${\varepsilon}_{Nd}(T)=-5.9$) and $1,735{\pm}260Ma$ (initial $^{87}Sr/^{86}Sr\;ratio=0.702{\pm}0.046,\;2{\sigma}$), respectively. Initial ${\varepsilon}_{Nd}$ value indicates that the magma should be derived from the crustal material. This initial ${\varepsilon}_{Nd}$ value also corresponds well with those from the Precambrian granitoids from North-China Craton rather than those of South-China Craton.

• The Journal of the Petrological Society of Korea
• /
• v.17 no.3
• /
• pp.144-153
• /
• 2008

Sr, Nd, Pb isotopic compositions of the Cenozoic basaltic rocks distributed in Pyeongtaek-Asan area display significantly enriched values compared with mid-ocean ridge basalts just like other Cenozoic basalts of Korea. The isotopic compositions of most of the Cenozoic basaltic rocks of Korea including those from Pyeongtaek-Asan area can be explained as mixing between enriched mantle component with relatively low $^{206}Pb/^{204}Pb$ ratios and depleted mantle component. In contrast, Jejudo basalts can be explained as mixing between enriched mantle component with realtively higher $^{206}Pb/^{204}Pb$ ratios and depleted mantle componsnt. Combined with that very similar division of enriched mantle components is applied to the Cenozoic basalts of northeast China and southeast China, it is suggested that subcontinental lithospheric mantle of central and southern parts of Korea represents eastern extension of North China Block and South China Block respectively. The indentation model for the late Paleozoic to early Mesozoic continental collision of China contradicts to such an interpretation, because it cannot explain occurrence of subcontinental lithospheric mantle component of South China Block-affinity under the Jejudo area. Instead, it is more probable that suture zone of the two continental blocks crosses between central and southern Korea and its location is further south from the Pyeongtaek-Asan area. Such distinct location compared with Imjingal belt, supposedly collisional boundary suggested before, suggests that mantle boundary may not be coincide with crustal boundary for the continental collision.

• Economic and Environmental Geology
• /
• v.37 no.4
• /
• pp.413-424
• /
• 2004

A paleomagnetic investigation of the Mesozoic Daedong Supergroup and the Precambrian Seosan Group in the Kyeonggi massif is carried out to elucidate the tectonic evolution of Korea under the effect of the collision between Korea and the North/South China Blocks. For the Daedong Supergroup, the characteristic direction of D/I=74.5$^{\circ}$/36.7$^{\circ}$(k=60.7, $\alpha$=5.1$^{\circ}$) after tilt correction is better clustered than that before tilt correction (D/I=61.9$^{\circ}$/52.8$^{\circ}$, k=4.4,$$\alpha$_{95}$=21.5$^{\circ}$), indi-cating that it is a primary magnetization acquired during the formation of the rock. Paleomagnetic pole position of the formation locates at 208.0$^{\circ}$E, 24.5$^{\circ}$N (n=14, K=67.5, $A_{95}$=4.9$^{\circ}$), statistically similar to those of Middle Triassic period of the SCB, revealing that the two had occupied the same tectonic unit during this period. It is observed that only 6 out of 33 sites of the Seosan Group yield remagnetized paleomagnetic direction. The rest of the sampling sites reveals severe dispersion of magnetic directions presumably due to the consequences of the collision between Korea and the North/South China Blocks. The characteristic direction of the Seosan Group is D/I=45.7$^{\circ}$/60.1$^{\circ}$(k=41.2,$$\alpha$_{95}$=10.6$^{\circ}$) and the corresponding pole is at 195.0$^{\circ}$E, 51.6$^{\circ}$N (n=6, K=20.8, $A_{95}$=12.4$^{\circ}$). Although the pole position is close to those of Jurassic period of the Kyeonggi massif and Early Cretaceous of the Kyeongsang basin. it is interpreted that the Seosan Group was remagnetized by the influence of the emplacement of the Jurassic Daebo Granite after or at the closing stage of the orogenic episode rather than under the direct effect of deformation and/or metamorphism caused by the collision.

• The Journal of the Petrological Society of Korea
• /
• v.21 no.2
• /
• pp.151-171
• /
• 2012

The Permo-Triassic Songrim orogeny in the Korean peninsula was a major tectonic event involving complicated continental collisions at the eastern margin of Eurasia. Based on the previous studies on the metamorphic and deformations features of the Songrim orogeny, this paper presents metamorphic and structural characteristics and timing of the Songrim orogeny in the Taebaeksan basin, and discuss about correlation of the tectono-metamorphic evolution of the Taebaeksan basin with the Okcheon basin and the Imjingang belt with a combined analysis of bulk crustal shortening direction, metamorphic P-T and T-t (time) paths. The metapelites in the Pyeongan Supergroup in the northeastern margin of the Taebaeksan basin have experienced lower-temperature/medium-pressure (LT/MP) regional metamorphism followed by high-temperature contact metamorphism due to the Jurassic granite intrusion. The earlier LT/MP regional metamorphism produced two loops of clockwise P-T-d (deformation) paths combined with four deformation events ($D_1-D_4$). The first loop concomitant with $D_1$ and $D_2$ occurred at $400-500^{\circ}C$, 1.5-3.0 kbar, and related with growth of syn-$D_1$ chloritoid and andalusite, post-$D_1$ margarite, Ca-rich syn-$D_2$ or post-$D_2$ plagioclase. The second loop accompanying $D_3$ and $D_4$ occurred at $520-580^{\circ}C$, 2.0-6.0 kbar, and associated with the growth of syn-$D_3$ garnet and staurolite, and syn-$D_4$ and/or post-$D_4$ andalusite porphyroblasts. Furthermore the syn-$D_1$ chloritoid and andalusite porphyroblasts grew during E-W bulk crustal shortening, whereas the syn-$D_3$ garnet and staurolite, and the syn-$D_4$ and/or post-$D_4$ andalusite porphyroblasts have grown under N-S bulk crustal shortening. The similarity in the characteristics and timing of the metamorphism and bulk crustal shortening directions between the Okcheon and Imjingang belts suggest that the peak metamorphic conditions tend to increase toward the western part (Imjingang belt and southwestern part of the Gyeonggi Massif) from the eastern part (Taebaeksan basin). The E-W bulk crustal shortening influenced the eastern part of the Okcheon belt, whereas the N-S bulk crustal shortening resulted in strong deformation in the Imjingang and Okcheon belts. Consequently, the Permo-Triassic Songrim orogeny in the Korean peninsula is probably not only related to collision of the North and South China blocks, but also to the amalgamation of terrane fragments at the eastern Eurasia margin (e.g., collision of the Sino-Korean continent and the Hida-Oki terrane).