• 한국지구과학회:학술대회논문집
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• 2005.02a
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• pp.138-144
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• 2005

석류석은 변성 온도와 압력을 계산하는 지온지압계에 널리 사용되며, 또한 이들 내부엽리와 외부엽리와의 접촉 관계를 이용하여 상대적인 변형작용의 시기를 밝히는 데 이용되어져 왔다. 석류석 반상변정 내의 내부 엽리 조직에 대한 정량적인 해석과 내부 미세 구조와 화학적 누대구조와의 관계에 대한 접근 방법은 석류석이 형성되는 동안에 온도-압력-변형작용의 진화 과정을 보다 정량적으로 해석할 수 있을 뿐만 아니라, 절대 연령 자료와 결합은 조산 운동 동안 발생하는 다변성/다변형 작용의 특징 보여주는 온도-압력-변형-시간 경로를 규명할 수 있다. 미국 메사추세츠 주 북중부 지역에서 십자석, 남정석과 함께 산출되는 석류석 반상변정은 온도-압력이 증가(540-570 $^{\circ}C$, 4.0-5.0 kbar에서 620-637 $^{\circ}C$, 7.9-8.8 kbar 까지) 하면서 성장하였다. 또한 이와 같은 변성작용 동안 압축 변형 방향은 다음과 같은 순서로, NE-SW, NW-SE, N-S 그 다음 E-W 방향으로 변화하였다. 결론적으로 이와 같은 변성작용과 변형작용은 주로 고생대 중기 데본기 동안에 일어났던 아카디안 조산운동으로 특징 지워 지며, 후기 알레게니안 조산운동에 부분적으로 영향을 받은 것으로 판단한다.

• Proceedings of the Mineralogical Society of Korea Conference
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• 2001.06a
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• pp.143-144
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• 2001

경기육괴의 남서부에 해당하며 옥천구조대의 북쪽에 위치한 백동-홍성 일대의 충청남도 일원에는 선캠브리아기의 편마암복합체내에 초염기성암체들이 소규모 렌즈상의 암체로 이 지역에 우세한 구조선 방향인 북북동 방향으로 배열되어 산출된다. 이들 초염기성암채들이 조산대에 형성되는 알파인형이며 전형적인 상부 맨틀기원의 암석이 부분용융된 맨틀 잔여물로서 지표로의 이동과정에서 변성작용을 받아 대부분은 사문석화 혹은 활석화된 것으로 보고되어 있다. 본 연구의 주대상인 변성염기성암을 포함하는 백동지역의 초염기성암은 홍성도폭내 덕정리 편암암체 내에 주변 편마암체와 단층으로 접하면서 나타난다. 덕정리 편마암체는 주로 각섬석 화강편마암으로 구성되어있다. 백동지역의 초염기성암내에는 변성염기성암이 층상으로 협재되어 나타난다. 이들 변성염기성암은 석류석, 단사휘석, 각섬석, 사장석으로 주로 이루어진 석류석 각섬암이며 금홍석도 포함하고 있다. 많은 석류석 주변에는 사장석과 각섬석으로 이루어진 심플렉타이트가 발달되어있다. 석류석 각섬암내 심플렉타이트가 형성되지 않은 석류석 가장자리로부터 계산된 변성 온도-압력 조건은 590-72$0^{\circ}C$, 9-l0kb이며 심플렉타이트가 잘 형성된 석류석 주변부로부터는 490-$600^{\circ}C$, 4-6.3kb의 변성 온도-압력 조건이 계산되었다. 이에 반해 변성염기성암을 포함한 초염기성암체 주변에 나타나는 석류석-각섬석 화강편마암으로 부터는 570-78$0^{\circ}C$, 11.6-l6kb의 변성 온도-압력 조건을 얻었다. 석류석 각섬암에서 석류석내에 포획물로 나타나는 휘석(Xjd, 4-11)이 기질에 나타나는 휘석(Xid, 1-6)보다 높은 제이다이트 성분을 갖는다. 이는 석류석 중심부가 석류석 주변부보다 변성압력 조건이 높았을 가능성을 지시한다. 즉 연구지역의 석류석 각섬암은 주변의 각섬석 화강편마암과 같이 에콜로자이트상-상부각섬암상-고압백립암상의 점이대에 해당하는 변성작용을 받은후 초염기성암의 사문암화 작용시기에 1차 후퇴변성작용을 그리고 그후의 활석화 시기에 심플렉타이트를 형성하는 2차 후퇴변성작용을 받았다. 이러한 후퇴변성작용시기에 많은 유체가 침입하였고 그 결과 초염기성암내의 변성염기성암이 주변 화강편마암보다 후퇴변성작용을 강하게 받았을 것으로 예상된다. 변성염기성암의 변성연대를 구하기 위해 두 석류석 각석암 시료에 대해 석류석-전암 Sm-Nd 등시선 연령을 구하였다. 두 개의 석류석 각섬암으로부터 계산된 전암-석류석 연령은 297.9$\pm$5.7(2$\sigma$)Ma 그리고 268.7$\pm$3.3(2$\sigma$)Ma를 나타낸다. 석류석의 Sm-Nd 폐쇄온도가 700-75$0^{\circ}C$임을 고려할 때 두 석류석 각섬암으로부터 계산된 연대는 최고 변성작용 혹은 초기 냉각 시기를 지시할 가능성이 높다. 한편 전암의 두 동위원소 자료로부터 계산된 전암의 연령은 408Ma이다. 이러한 연구 결과는 연구지역의 석류석 각섬암이 시루리아기 후기 혹은 데본기 초기에 관입 후 석탄기 후기에서 페름기 중기에 주변 화강편마암과 함께 섭입작용을 받았을 가능성을 지시한다.

• Proceedings of the Petrological Society of Korea Conference
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• 2002.05a
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• pp.1-38
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• 2002

옥천변성대 서남부지역은 변성이질암의 광물조합을 기준으로 남동부부터 북서방향으로 흑운모대, 석류석대, 십자석대의 3개의 변성광물분대로 나누어진다. Oh et al. (1995a)의 연구에서 보고된 남정석들은 산출되지 않는 것이 확인되었고 변성도는 흑운모대에서 석류석대를 거쳐 십자석대로 갈수록 증가한다. 쥬라기 화강암 접촉부의 국부적인 변성암류에서는 화강암에 의한 접촉변성작용에 의해 형성된 홍주석과 규선석이 산출된다. 흑운모대의 변성 압력-온도는 4.2 - 5.1 kb, 400 - 500 $^{\circ}C$이다. 십자석대의 정누대구조를 가지는 석류석과 석류석안의 사장석, 흑운모, 금흥석, 일메나이트포유광물의 공생관계로 추정한 압력-온도 (석류석 주변부: 7.0 - 8.0 kb, 550 - 620 $^{\circ}C$； 석류석 중심부: 4.0 - 5.0 kb, 420 - 520 $^{\circ}C$) 및 십자석대 내에서 후퇴변성작용 및 접촉변성작용 받은 석류석 주변부에 기록된 압력-온도 조건(약 2.0 - 3.0kb, 450 - 55$0^{\circ}C$)과 함께 옥천변성대 서남부지역의 변성암류가 시계방향의 압력-온도 경로를 겪었음을 지시한다. 연구지역 내에서 정밀 기재된 단면들에 대한 퇴적환경을 종합하면 대체 적으로 남동부에서는 천해성 환경이 인지되나 북서쪽으로 갈수록 대륙사면을 거쳐 분지 중심의 환경으로 전이되는 경향을 보인다. 이러한 퇴적상의 공간적 분포는 분지의 남동쪽보다 북서쪽의 침강이 우세하였던 것으로 해석될 수 있으며, 이는 곧 분지가 형성될 때 반지구대 (half graben) 형태로 분지가 열개 (rifting) 되었음을 의미한다. 각 변성분대에서 채취한 변성이질암으로부터 측정된 K-Ar 과 40Ar/39Ar 흑운모와 백운모 연대들은 149 - 167 Ma에 집중된다. 그리고 각 변성분대에서 동일시료에 대한 K-Ar 과 40Ar/39Ar 연대들은 동일시기를 지시함으로 연대적인 신뢰성을 확인 할 수 있었다. 옥천변성대 서남부지역의 변성암류를 관입하는 2개의 괴상의 화강암과 1개의 엽리화강암에서 얻어진 백운모와 흑운모들의 K-Ar 연대는 모두 156 Ma이며 옥천변성대 서남부지역의 변성이 질암의 연대와 유사하다. 이는 연구지역의 변성암류와 화강암류는 40Ar/39Ar 과 K-Ar 계의 흑운모와 백운모의 폐쇄온도 (약 300 - 350 $^{\circ}C$) 까지 동시에 냉각된 사실을 지시한다. 각섬석 편암내의 각섬석들은 복잡한 40Ar/39Ar 연대를 보여주며 일부가 평형연대를 보여주지만 특별한 의미 부여가 힘들다.

• The Journal of the Petrological Society of Korea
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• v.8 no.3
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• pp.183-202
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• 1999

The Sobeaksan Gneiss Complex in the Punggi area is composed of mainly mignatitic gneiss, porphyroblastic gneiss, garnet granitic gneiss and biotitie granitic gneiss. Metamorphic grade increase gradually from the amphibolite facies of northwestern part to the granulite facies of southwestern part in the study area. Representative mineral assemblage in the amphibolite facies is biotite-muscovite-K-feldspar-plagioclase$\pm$garnet$\pm$epidote, needle shape or fibrous sillimanite occur in transitional zone from the amphibolite facies to the granulite facies. In the granulite facies, the garnet-Opx granulite shows garnet-orthopyroxene-biotite-plagioclase, the metabasite shows clinopyroxene-plagioclase$\pm$hornblende$\pm$orthopyroxene$\pm$garnet and the migmatitic gneiss shows garnet-biotite-sillimanite-cordierite$\pm$spinel as representative mineral assemblage. Retrograde metamorphism after the granulite facies metamorphism made corindum and andalusite in the migmatitic gneiss and the thin layer garnet between clinopyroxene and plagioclase in the metabasites. The peak P-T conditions of the migmatitic gneiss and the garnet-Opx granulite are $916^{\circ}C$/6.6 kb and $826^{\circ}C$/6.3 kb, respectively. The P-T condition of biotite and plagioclase inclusion, which indicates the progressive condition of the granulie facies, within garnet is $866^{\circ}C$/7.5 kb and that of rim composition of garnet and biotite is $726^{\circ}C$/4.6 kb, which infer the clockwise P-T path of the granulite facies metamorphism. The temperatures caculated by the rim composition of garnet and biotite in the migmatitic gneiss and garnet granitic gneiss have a wide range of $556-741^{\circ}C$, which indicate that the retrograde metamorphism after the granulite facies metamorphism has effected differently. It is difficult to determine the P-T condition of the biotite granitic gneiss because less occurrence and higher spessartine content of garnet. The P-T condition of the thin layered garnet between clinopytoxene and plagioclase in the metabasite is $635-707^{\circ}C$/4.1-5.3 kb. This texture indicates the isobaric cooling(IBC) condition of the retrogressive metamorphism. As a result, the metamorphic evolution of the Punggi area has undergone the isobaric cooling after the granulite facies metamorphism which has undergone the clockwise P-T path.

• The Journal of the Petrological Society of Korea
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• v.8 no.2
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• pp.106-124
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• 1999

In the Cheongju-Minwon area which occupies the middle part of the Ogcheon Metamorphic Belt, three metamorphic events(M1, M2, M3) had occurred. Intermediate P/T type M2 regional metamorphism formed prevailing mineral assemblages in the study area. Low PIT type M3 contact metamorphism occurred due to the intrusion of granites after M2 metamorphism. M1 metamorphism is recognized by inclusions within garnet. During M2 metamorphism, the metamorphic grade increased from the biotite zone in the southeastern part to the garnet zone in the northwestern part of the study area. This result is similar to the metamorphic evolution of the southwestern part of the Ogcheon Metamorphic Belt. Garnets in the garnet zone are classified into two types; Type A garnet has inclusions whose trail is connected to the foliation in the matrix and Type B garnet has inclusion rich core and inclusion poor rim. Type A garnet formed in the mica rich part with crenulation cleavage whereas Type B garnet formed in the quartz rich part with weak crenulation cleavage. In some outcrops, two types garnets are found together. Compared to the rim of Type A garnet, the rim of Type B garnet is lower in grossular and spessartine contents but higher in almandine and pyrope contents. In some Type B garnets, the inclusion poor part is rimmed by muddy colored or protuberant new overgrowth. In the inclusion poor part and new overgrowth, a rapid increase in grossular and decrease in spessartine is observed. However, the compositional patterns of Type A and B are similar; Ca increases and Mn decreases from core to rim. Two types garnets formed mainly due to the difference of bulk chemistry instead of metamorphic and deformational differences. The metamorphic P-T conditions estimated from Type A garnets are 595-690 OC15.7-8.8 kb, which indicates M2 metamorphism is intermediate P/T type metamorphism. On the other hand, a wide range of P-T conditions is calculated from Type B garnets. The P-T conditions from most Type B garnet rims are 617-690 OC16.2-8.9 kb which also indicates an intermediate P/T type metamorphism. However, at the rim part with flat end or weak overgrowth, grossular content is low and 573-624OC14.7-5.8 kb are estimated. The P-T conditions calculated from plagioclase and biotite inclusions in garnet are 460-500 0C/1.9-3.0 kb. The P-T conditions from rim part with weak overgrowth and inclusions within garnet, indicate that low P/T type M1 regional metamorphism might have occurred before intermediate P/T type M2 regional metamorphism. The P-T conditions estimated from samples which had undergone low PIT type M3 metamorphism strongly, are 547-610 0C/2.1-5.0 kb.

• 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.

• Journal of the Korean earth science society
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• v.29 no.3
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• pp.221-245
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• 2008

The precambrian granitic gneiss and porphyroblastic gneiss are widely distributed in the Gwangyang-Hadong area of Korea. This study focuses on the geochemical properties and metamorphic P-T conditions of these gneisses. These gneisses are plotted according to granodiorite domain on an IUGS silica-alkali diagram. Geochemical properties of major elements suggest that these rocks are of the sub-alkalic rock series, and were farmed from S-type magmas which were generated in a syn-collision tectonic environment. The amounts of trace elements (Zn, Sc, Sr, V, etc.) decreased as $SiO_2$ concentrations increased. Almandine and spessartine mol%'s and XFe are higher in garnet rims, while pyrope mol%'s are higher in the garnet cores. This seems to be the result of garnet growth and retrogressive metamorphism. Metamorphic zones are divided into sillimanite-cordierite, sillimanite, garnet, and biotite zones. Metamorphic P-T conditions estimated from the gneisses indicate high temperature and low to medium pressure metamorphism (689-757$^{\circ}C$, 5.0-5.6 kbar), followed by medium temperature, low pressure retrorade metamorphism (579-628$^{\circ}C$, 3.1-4.5 kbar), and overprinted retrogade metamorphism (502-558$^{\circ}C$, 1.6-2.3 kbar).

• The Journal of the Petrological Society of Korea
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• v.10 no.2
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• pp.57-81
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• 2001

In the amphibolites of the Hwanggangri area, three metamorphic zones are established like hornblende-actinolite zone (H-AZ), hornblende zone (HZ) and diopside zone (DZ) by the main mineral assemblages. Hornblende zone and hornblende-actinolite zone develope away from the diopside zone that experienced the highest thermal effect. Thus, this pattern identifies the decreasing metamorphic grade of the contact metamorphism with increasing distance from the granitic pluton. The mineral assemblages of this rock are classified into six representative groups such as $\circled1$ actinolite+plagioclase+chlorite, $\circled2$ actinolite+hornblende+plagioclase+chlorite$\pm$epidote$\pm$biotite, $\circled3$ actinolite+hornblende+plagioclass$\pm$biotite$\pm$epidote, $\circled4$ hornblende+plagioclase$\pm$biotite$\pm$chlorite, $\circled5$ hornblende+plagioclase+diopside+actinolite$\pm$epidote$\pm$chlorite, $\circled6$hornblende+plagioclase+diopside$\pm$biotite$\pm$epidote. Two metamorphic events m recognized in the amphibolites of the study area that the first metamorphism is the regional metamorphism dominantly occurred in the whole Ogcheon metamorphic belt and it gave rise to the growth of actinolite at the core or center of the amphibole grains of coarse and medium size. Its metamorphic grade ranges from the greenschist facies to epidote-amphibolite facies. The second metamorphism overlapped is the contact metamorphism caused by the adjacent granitic pluton, and its metamorphic grade is thought to reach to the low pressure part of upper amphibolite facies. According to the calculation by TWEEQU thermobarometry and amphibole-plagioclase thermometry, the metamorphic temperature of initial regional metamorphism is $439-537^{\circ}C$ under pressure of 4.6-7.3 kb and its peak temperature and pressure are considered to reach to the range of 492-537 and 5.2-7.3 kb. And the temperature range of contact metamorphism occurred by intrusion of cretaceous granitic body, is $588-739^{\circ}C$ under pressure of 2.6-5.2 kb and its peak temperature and pressure are estimated as having the range of $697-739^{\circ}C$ and 3.8-5.2 kb that this amphibolites are estimated to pass through the metamorphic evolution of both the rise of temperature and the drop of pressure.

• The Journal of the Petrological Society of Korea
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• v.6 no.3
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• pp.226-243
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• 1997

The Odesan Gneiss Complex consists of mainly migmatitic gneiss and porphyroblastic gneiss with locally intercated quartzite, amphibolite, marble and leucocratic gneiss. At least two different regional metamorphisms are recognized in the study area. Metamorphic grade of the first metamorphism increases from the K-feldspar-muscovite zone(in which biotite-muscovite-plagioclase-quartz and garnet-biotite-muscovite-K-feldspar-plagioclase-quartz assemblages occur) in the east and southwestern part of the study area to the K-feldspar-garnet zone(in which garnet-biotite-K-feldspar-plagioclase-quartz, biotite-K-feldspar-plagioclase-quartz, garnet-biotite-K-feldspar-plagioclase-sillimanite-spinel-quartz assemblages occur) in the northwestern part. Kyanite is found as inclusions in plagioclase. The second metamorphism is characterised by occurrence of cordierite. The metamorphic grade of 2nd metamorphism decreases radically from the central-western part near Gaeinsan in which cordierite-garnet-sillimanite-biotite-muscovite-quartz, cordierite-garnet-spinel-sillimanite-biotite-muscovite-quartz assemblages representing the garnet-cordierite zone are observed. The garnet-cordierite zone is surrounded by the sillimanite-cordierite zone which shows cordierite-sillimanite-biotite-plagioclase, cordierite-muscovite-biotite-plagioclase and sillimanite-muscovite-biotite-plagioclase assemblages. The peak metamorphic P-T conditions of the first metamorphism calcuted from garnet-biotite-sillimanite-K-feldspar-plagioclase-spinel assemblage are 5.4~7.4 kb and $776-789^{\circ}C$. Real P-T condition of the first metamorphism might be higher than the calcuated P-T condition according to the study based on the phase equilibria. P-T conditions calcuated from the garnet-biotite in plagioclase are 12.5kb and $650^{\circ}C$ which indicate that the P-T path of the first metamorphism had passed a high pressure condition before the peak metamorphic temperature condition. The peak metamorphic P-T conditions of the second metamorphism calcuated from garnet-biotite-cordierite-spinel-quartz assemblage are $680~750^{\circ}C$ at pressures lower than 6 kb. In the Odesan Gneiss Complex, the first metamorphism of medium pressure and high temperature had occurred after the high pressure condition and fast uplift and then the second metamorphism of low pressure condition occurred after sedimentation of the Kuryong Group.

• The Journal of the Petrological Society of Korea
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• v.11 no.3_4
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• pp.121-137
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• 2002

Metamorphic evolution of the Ogcheon metamorphic belt has been studied by many investigators for the past few decades. P-T conditions of the Ogcheon metamorphic belt were estimated as 4.2-9.4 kbar and $490-630^{\circ}C$, corresponding to the medium-pressure type. In addition, the clockwise P-T-t path suggests a crustal-thickening event in association with the formation of thrust nappes. However, some details on deformation and orogeny of the Ogcheon metamorphic belt have been ambiguous yet. Although the metamorphic age has been also equivocal, recent isotopic studies strongly suggest that the peak metamorphism in the Ogcheon metamorphic belt has occurred at ca. 300-280 Ma between Late Carboniferous and Early Permian. It is thus inferred that the Ogcheon metamorphic belt and the Taebaegsan basin have evolved as separate terranes and that both were sutured at ca. 250-220 Ma. These results are partly in contrast with those of previous workers and require a revised framework for tectonic evolution of the Ogcheon belt. In addition, it is likely that the Ogcheon belt is correlative with the Hida marginal belt and the Hida metamorphic belt.