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

• The Journal of the Petrological Society of Korea
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• v.7 no.3
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• pp.190-206
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• 1998

The microstructures and time-relationship between deformation and growth of metamorphic minerals(metamorphism) of the Paleozoic metasedimentary rocks(Joseon Supergroup and Pyeongan Group) in the Janggunbong area at the central-south part in the North Sobaegsan Massif, Korea, have been analyzed in this paper. The first phase metamorphism (low-pressure type metamorphism), recognized as the crystallization of stack-type chloritoid and biotite and augen-type old andalusite, occurred under non-deformational condition before D1 deformation related to the formation of an E-W trending isocline-synclinal fold(Janggunbong fold) and associated its axial plane S1 foliation, and produced regional mineralogical zoning of E-W trend in the Paleozoic rocks. The second phase metamorphism(medium-pressure type metamorphism), related to the growth of staurolite and garnet porphyroblasts with straight or curved internal foliations(Si), occurred under non-deformational condition after D1 deformation related to the formation of E-W trending thrusts modifying the Janggunbong fold and during D2 deformation related to the formation of E-W trending Yecheon shear zone. This metamorphism also produced regional mineralogical zoning of E-W trend. After D2 deformation occurred the intrusion of Jurassic Chunyang granite and associated its contact metamorphism which crystallized patchy-type young andalusite and prismatic- or fibrous-type sillimanite and coarse-grained garnet. This metamorphism occurred under non-deformational condition before D3 deformation related to the formation of S3 crenulation cleavage and during early phase of D3 deformation, and formed narrow mineralogical zoning of N-S trend near Chunyang granite.

• The Journal of the Petrological Society of Korea
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• v.15 no.1 s.43
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• pp.10-24
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• 2006

Staurolite grains in staurolite, kyanite and sillimanite zones occurred in the Littleton Formation, Northcentral Massachusetts have interpreted to form by Barrovian-type metamorphism during Acadian orogeny. However, various occurrence of staurolite in the three zones, (a) porphyroblast, (b) randomly oriented and coarse-grained muscovite pseudomorph after staurolite, (c) recrystallized staurolite at the margin of garnet porphyroblast and within the pseudomorph, indicates that they have resulted from polymetamorphism. Staurolite in these three metamorphic zones can be formed by demise of chlorite or chloritoid that depends on difference of bulk-rock compositions and changes of P-T conditions. Staurolite modal proportion calculated in MnNCKFHASH system using THERMOCALC program reveals that staurolite could have grown with garnet with increasing pressure and temperature, if it coexist with chlorite. After demise of chlorite and appearance of biotite, staurolite mode decrease with increasing pressure and temperature. Therefore, based on the previous P-T paths for the Acadian metamorhism, staurolite porphyroblast grew with garnet during 400-370 Ma. Randomly oriented and coarse-grained muscovite pseudomorphs after staurolite probably have grown due to heating with appearance of kyanite and sillimanite. Consequently, pseudomorphisrn of staurolite occurred by heating derived from locally intense Alleghanian shearing (ca. 320-300 Ma) overprinted the Acadian metamorphism. Recrystallized fine-grained staurolite in sillimanite zone observed between the grain boundaries of muscovite in the pseudomorphs and at the edge of garnet porphyrobasts has formed during decreasing temperature and pressure (ca. 300-280 Ma) after peak temperature (ca. $700^{\circ}C$) of the Allegllanian metamorphism.

• Economic and Environmental Geology
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• v.24 no.2
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• pp.97-105
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• 1991

Oxygen and sulfur isotope composition of pyrophyllite and pyrite from six pyrophyllite deposits in the Yangsan-Milyang areas (the Cheonbulsan, Dumyong, Dongrae, Youkwang, Sungjin and Milyang mines), and five deposits in the Whasoon-Dado-Haenam areas (the Byuksong, Songseok, Dado, Bugock and Nowha mines) were measured. Pyrophyllite ores both from the Yangsan-Milyang areas and the Dado-Haenam areas are composed mainly of high alumina minerals such as pyrophyllite, sericite and kaolinite. Most of altered rocks show diagnostic chacteristics of bleaching effect. Major minerals of the Songseok ore deposit in the Whasoon area are pyrophyllite, and diaspore with minor amounts of kaolinite and quartz. The Byuksong ores from the Whasoon area were composed mainly of andalusite, kaolinite, pyrophyllite and mica with small amounts of chloritoid, quartz and carbonaceous matter. The Byuksong and Songseok ores show metamorphic textures such as porphyroblastic, and pressure solution textures, and have low whiteness values, The ${\delta}^{18}O$ values of pyrophyllite from the Cheonbulsan and Dumyong mines in the Yangsan area, and the Dado and Nowha mines in the Dado-Haenam areas were in the range of 0.23~5.36%,. The relatively low 8 180 values provide conclusive evidence for hydrothermal activity in these deposits. The ${\delta}^{18}O$ values of pvrophvllite from the Songseok mine in the Whasoon area were measured as 6.70-8.13%, and these higher ${\delta}^{18}O$ values suggest that the Songseok ore deposit have been probably subjected to metamorphism. ${\delta}^{34}$S(pyrito) values from the Cheonbulsan, Dumyong, Youkwang, Dongrae, Sungjin and Milyang deposits in the Yangsan-Milyang areas, and the Dado pyrophyllite deposits in the Dado area range from -5.8 to 2.7%, which means that the pyrite sulfur could be of igneous origin. ${\delta}^{34}$S(pyrito) from the Nohwa mine in the Haenam area is, however, measured as -12.4%" implying the contamination of sulfur derived from the sedimentary country rocks. All of the studied high alumina deposits in the Yangsan-Milyang areas and the Dado-Haenam areas were hydrothermal in origin, whereas the Byuksong and Songseok ore deposits in the Whasoon area were probably of metamorphic origin.

• Economic and Environmental Geology
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• v.52 no.5
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• pp.367-379
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• 2019

Pyeongan Supergroup (PS) in the Taebaeksan basin preserves key geological evidences to understand the tectonometamorphic evolution of the Songrim orogeny that affected the formation of the Korean Peninsula during the late Paleozoic to early Mesozoic. The aims of this paper therefore are to investigate the characteristics of the Songrim orogeny based on the previous results of metamorphism and deformations of the PS, and then to review geological significance and research necessity of the PS. Age distributions and Th/U ratio of detrital zircon in the PS indicate that sedimentary environment of the Taebaeksan basin during the late Paleozoic was arc-related foreland basin and retro-arc foreland basin at the active continental margin. In addition, the main magmatic activities occurred in the early Pennsylvanian and Middle Permian, thus sedimentation and magmatic activities occurred simultaneously. The PS was affected by lower temperature-medium pressure (M1) and medium temperature and pressure (M2) regional metamorphism during the Songrim orogeny. During M1, slate and phyllite containing chloritoid, andalusite, kyanite porphyroblasts intensively deformed by E-W bulk crustal shortening combined with folding and shearing. And garnet and staurolite porphyroblasts were formed during the N-S bulk crustal shortening accompained by M2. Such regional metamorphism of the PS is interpreted to occur in an area where high strain zone is localized during ca. 220-270 Ma. In order to elucidate the evolution of the Taebaeksan basin and tectonic features of the Songrim orogeny, it is expected that the study will be carried out such as the regional distribution of metamorphic zones developed in the PS, characteristics and timing of deformations, and late Paleozoic paleo-geography of the Taebaeksan basin.