• Journal of the Mineralogical Society of Korea
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• v.25 no.1
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• pp.1-8
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• 2012

The metamorphic environments occrrred in the Sadong and the Gobangsan formations were studied through the investigation of chloritoid and white mica in shales at Munkyung area. Two types of white mica occurs in the shale of Sadong formation; muscovite-dominant ($Mu_{76.1}Pa_{18.1}Ma_{5.8}$) and margarite-dominant ($Ma_{52.9}Mu_{31.6}Pa_{15.5}$). It is inferred that the muscovite-dominant white mica is generated by the diagenesis of Na-rich illite whereas the margarite-dominant white mica is generated by reactions between calcite and pyrophyllite separated from illite. In shales of the Gobangsan formation, chloritoids are observed with muscovite, pyrophyllite and chlorite. The chloritoids of the Gobangsan formation are considered to be originated from the reaction between pyrophyllite and chlorite. The Sadong and Gobangsan formations would have experienced the low-temperature metamorphism (anchizone) considering that white mica in general forms above the temperature of $200^{\circ}C$ and the assemblage of chloritoid-pyrophyllite-chlorite is stabilized below $280^{\circ}C$.

• Journal of the Mineralogical Society of Korea
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• v.26 no.1
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• pp.55-64
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• 2013

The generation of staurolite from the mixed-phase muscovite and the metamorphic environment of shales in the Baekunsa formation, Hongsan, Buyeo, were studied using electron probe micro analysis (EPMA). The average chemical composition of mica-type mineral is $(K_{1.11}Na_{0.26}Ca_{0.04})(Al_{3.93}Fe_{0.21}Mg_{0.07})(Si_{6.08}Al_{1.92})O_{20}(OH)_4$, and shows a characteristics of the so-called illite with a low content of interlayer cations and Fe, Mg in octahedral sites. The mica-type mineral shows a typical chemical composition of the mixed-phase among muscovite, pyrophyllite, and chlorite (mixed-phase muscovite, $Mu_{70.5}Py_{23.5}Ch_{6.0}$). The staurolite, in general, occurs with the mixed-phase muscovites, pyrophyllites, and aluminosilicates in the rock. We consider that staurolite can be formed by a reaction involving pyrophyllite such as pyrophyllite+chloritoid. The chloritoid is formed by a reaction between pyrophyllite and chlorite and is supposed to be used up in the process of staurolite formation. As a result, the mixed-phase muscovite, formed during the transition of illite to muscovite, plays an important role for the generation of the staurolite. Considering that the reaction occurs at the temperature higher than $300^{\circ}C$ and pyrophyllites transform into aluminosilicates at $350^{\circ}C$, the shale in the Baekunsa formation can be considered to have been experienced a metamorphic temperature between $300{\sim}350^{\circ}C$.

• 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.