• Economic and Environmental Geology
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• v.21 no.3
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• pp.235-255
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• 1988

Talc deposit of pipe-like form occurrs in the lower part of the Hyangsanri Dolomite with a strike of N40 -50 E and a dip of 40 -50 NW which is one formation of the Ogcheon Super Croup. The pipi-like ore body plunge at about $40^{\circ}$ to the west and are parallel to the lineation developed in the area. Structural formulae of tales occurred in this deposit are close to the ieal composition $Mg_6Si_8O_{20}(OH)_4$ showing limited deviation from ideal one. Substitution of Al for Si in tetrahedral site is of little or nothing ranging 0-0.04 and octahedral occupancy is close to six ranging 5.88-5.98 atoms per unit cell. Predominant octahedaral cation is Mg and proportion of divalent cations is generally over 97percent. Calcite -dolomite thermometry is obtained by determining the mol % $MgCO_3$using of EPMA and XRD methods. The peak metamorphic temperature can be estimated at $470{\pm}30^{\circ}C$ in the area whereas carbonates occurred at near talc ore show lower temperature than $400^{\circ}C$ that the calcite solvus limit is not well established. It indicates that the talc deposit was formed at the lower temperature that the metamorphic temperature. Cosequently, the formation of talc by metamorphism is questionable and the alteratin zone developed around the talc ore is very limited. The occurrence of talc ore in the dolomite as well as mineralogy, calcite-dolomite geothermometry, chlorite geothermometry, field and microscopic evidence suggest that siliceous ascending hydrothermal solution along the fracture is responsible for the formation of talc. It was considered that the slight fracturing of dolomite was formed by deformation prior to the mineralization.

• Economic and Environmental Geology
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• v.6 no.4
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• pp.201-216
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• 1973

Being believed thus far to be distributed in the wide areas in the vicinity of Seoul, the capital city of Korea, the Yonchon System in its type locality in Yonchon-gun from which the name derived was never previously traced down or correlated to the Precambrian metamorphic complex in Seoul area where the present study was carried out. Due to in accessibility to Yonchon area, the writer also could not trace the system down to the area studied so as to correlate them. The present study endeavored to differentiate general stratigraphy and interprete the structure of the metamorphic complex in the area. In spite of the complexity of structure and rapid changes in lithofacies of the complex, it was succeeded to find out the key bed by which the stratigraphy and structure of the area could be straightened out. The keybeds were the Buchon limestone bed in the western parts of the area; Daisongri quartzite bed cropped out in the southeastern area; Jangrak quartzite bed scattered in the several localities in the northwest, southwest, and eastern parts of the area; and Earn quartzite bed isolated in the eastern part of the area. These keybeds together with the broad regional structure made it possible to differentiated the Precambrian rocks in ascending order into the Kyonggi metamorphic complex, Jangrak group and Chunsung group which are in clinounconformable relation, and the first complex were again separated in ascending order into Buchon, Sihung, and Yangpyong metermorphic groups. Althcugh it has being vaguely called as the Yonchon system thus far, the Kyonggi metamorphic complex have never been studied before. The complex might, however, belong to early to early-middle Precambrian age. The Jangrak and Chunsung group were correlated to the Sangwon system in North Korea by the writer (1972), but it became apparent that the rocks of the groups have different lithology and highly metamorphosd than those of the Sangwon system which has thick sequence of limestone and slightly metamorphosed. Being deposited in the margin of the basin, it is natural that the groups poccess terrestrial sediments rather than limestone, yet no explanation is at hand as to what was the cause of bringing such difference in grade of metamorphism. Thus the writer attempted to correlate the both groups to those of pre-Sangwon and post-Yonchon which might be middle to early-late Precambrian time. Judging from difference in grade of deformation and unconformity between the Kyonggi metamorphic complex, Jangrak group, and Chunsung group, three stages of orogeny were established: the Kyonggi, Jangrak orogenies, and Chunsung disturbance toward younger age. It is rather astonishing to point out that the structure of these Precambrian formations. was not effected by Daebo orogeny of Jurassic age. The post-tectonic block faulting was accompanied by these orogenies, and in consequence NNE and N-S trending faults were originated. These faulting were intermittented and repeated until Daebo orogeny at which granites intruded along these faults. The manifestation of alignment of these faults is indicated by the parallel and straight linear development of valleys and streams in the Kyonggi Massifland.

• Economic and Environmental Geology
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• v.45 no.4
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• pp.465-476
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• 2012

The Anatolia peninsula consists of several continental fragments that include the Pontide Block in north and the Anatolide-Touride Block in south as well as the Arabian Platform in southeast. These continental blocks were joined together into a single landmass in the late Tertiary. During most of the Phanerozoic these continental blocks were separated by paleo-oceans, such as Paleo-Tethys and Neo-Tethys. The Pontide Block in north show Laurasian affinities, and was only slightly affected by the Alpide orogeny; they preserve evidence for the Variscan and Cimmeride orogenies. The Pontic Block is composed of the Strandja, Istanbul and Sakarya zones that were amalgamated into a single terrane by the mid Cretaceous times. The Anatolide-Tauride Block in south shows Gondwana affinities but was separated from Gondwana in the Triassic and formed an extensive carbonate platform during the Mesozoic. The Anatolide-Tauride Block was intensely deformed and partly metamorphosed during the Alpide orogeny; this leads to the subdivision of the Anatolide-Tauride Block into several zones on the basis of the type and age of metamorphism and deformation. The Arabian Platform in southeast forms the northernmost extension of the Arabian Plate that shows a stratigraphy similar to the Anatolide-Tauride Block with a clastic-carbonate dominated Palaeozoic and a carbonate dominated Mesozoic succession. A new tectonic era started in Anatolia Peninsula in the Oligocene-Miocene after the final amalgamation of these continental blocks and plate. This neotectonic phase is characterized by extension, and strike-slip faulting, continental sedimentation, and widespread calcalkaline magmatism, which played a very important role in producing beautiful landscapes of the Anatolia Peninsula today.

• The Journal of the Petrological Society of Korea
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• v.9 no.1
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• pp.13-28
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• 2000

Chojeong area is mainly composed of the Ogcheon Group which consists of regionally metamorphosed, age-unknown sedimentary rocks. In the northwestern parts, the Group is intruded by the Jurassic Daebo granite and Cretaceous felsic and mafic dykes. The lowermost, Midongsan Formation which consists of milky white impure quartzite, crops out along the anticline axes with N40E trend. Ungyori quartzite Formation is intercalated with quartzite and slate. Miwon Formation is most widely exposed in the area and consists mainly of phyllitic sandy rocks with a thin crystalline limestone bed. Hwajeonri Formation is divided into two parts, pelitic lower and calcareous upper parts, composed with phyllite and slate. Changri and Hwanggangri Formations are typical members of Ogcheon Group, the former bearing coally graphite seams consists mainly of black slate and phyllite with intercalated greenish grey phyllite, the latter is pebble bearing phyllite formation of which matrix and pebbles are variable in compositions and size. Biotite granite, porphyritic granite and two mica granite belong to Jurassic so-called Dabo granite. They intruded the Ogcheon Group forming vast contact metarnophic zone. Quartz porphyry, mafic dyke and felsite intruded along the marginal zone of porphyritic granite batholith and fracture of NS trend. Main structural lineaments in Ogcheon Group shows N25-45E, NS and N30-45W trends. The N25-45E trends are mainly from general ductile deformation during regional metamorphism, showing isoclinal folding, Fl foliations and lithological erosional characters. Some of these trends are due to normal faults. The NS and N30-45W trends represent brittle deformation including faults and joints. In the area of granitic batholith, NS to N30- 45 trends are from the direction of dykes. In the soils of the area, average contents of heavy metal elements such as Cd, Cr, Cu, Pb, and Zn are 0.2, 50.6, 35.5, 27.9, and 93.4 ppm respectively, which are not higher than the average values of natural soils, under the tolerable level. Enrichment Index does not show any heavy metal pollution in the area. Average depths of weathering(5m vs. 2m), porosities(43.94 vs. 51.80), densities(l.29 vs. 1.15), and permeabilities(2.52 vs. 8.07) are comparable in granite areas and in the phyllite areas of Ogcheon Group.

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