Pb-Pb age and uplift history of the Busan gneiss complex in the Okchon Belt, Korea: A comparison with the Bagdalryeong gneiss complex in the Kyongki Massif

Hee Sagong, Sung Tack Kwon

Research output: Contribution to journalReview article

14 Citations (Scopus)

Abstract

The Busan gneiss complex is a unique body in the Okchon Belt in that it consists of high-grade gneisses surrounded by low-grade schists. In order to elucidate the origin of the Busan gneiss complex, we compared Pb isotope data from the complex with those from the nearby Bagdalryeong gneiss complex of the Kyongki Massif. The two complexes share common lithology, i.e., migmatitic gneiss and augen gneiss. The Pb data of whole rock and feldspar from the two complexes appear to form a single linear array in the 207Pb/ 204Pb-206Pb/204Pb diagram, corresponding to an age of 1932±65 (1σ) Ma. It represents either the formation age or the age of high-grade metamorphism, i.e., migmatization. The Th/U ratios calculated from the 208Pb/204Pb and 206Pb/ 204Pb data of both complexes show a close relationship in lithology. The Pb isotope data suggest that the two complexes were originally one continuous body and experienced a similar geologic history since the early Proterozoic. Thus, we conclude that the Busan gneiss complex is either an extension of the basement rocks of the Kyongki Massif beneath the Okchon Belt or a tectonically emplaced piece of the Kyongki Massif. We reinterpret reported Rb-Sr muscovite and biotite ages for the Busan and Bagdalryeong gneiss complexes as the cooling age. The Rb-Sr muscovite ages were originally interpreted as the reset (or partially reset) ages during the Triassic metamorphism of the Okchon Belt (Cliff et al., 1985). Our alternative interpretation suggests that the Bagdalryeong gneiss complex was uplifted rapidly during the Jurassic, whereas the Busan gneiss complex was uplifted slowly since the late Permian. The fast uplift of the Bagdalryeong gneiss complex might have been related to the normal shear movement between the Kyongki Massif and the Okchon Belt (Ree et al., 1995).

Original languageEnglish
Pages (from-to)99-106
Number of pages8
JournalGeosciences Journal
Volume2
Issue number2
DOIs
Publication statusPublished - 1998 Jan 1

Fingerprint

gneiss
uplift
history
muscovite
lithology
metamorphism
augen gneiss
isotope
comparison
migmatization
basement rock
schist
feldspar
biotite
Proterozoic
Permian
Triassic
Jurassic
diagram
cooling

All Science Journal Classification (ASJC) codes

  • Environmental Science(all)
  • Earth and Planetary Sciences(all)

Cite this

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title = "Pb-Pb age and uplift history of the Busan gneiss complex in the Okchon Belt, Korea: A comparison with the Bagdalryeong gneiss complex in the Kyongki Massif",
abstract = "The Busan gneiss complex is a unique body in the Okchon Belt in that it consists of high-grade gneisses surrounded by low-grade schists. In order to elucidate the origin of the Busan gneiss complex, we compared Pb isotope data from the complex with those from the nearby Bagdalryeong gneiss complex of the Kyongki Massif. The two complexes share common lithology, i.e., migmatitic gneiss and augen gneiss. The Pb data of whole rock and feldspar from the two complexes appear to form a single linear array in the 207Pb/ 204Pb-206Pb/204Pb diagram, corresponding to an age of 1932±65 (1σ) Ma. It represents either the formation age or the age of high-grade metamorphism, i.e., migmatization. The Th/U ratios calculated from the 208Pb/204Pb and 206Pb/ 204Pb data of both complexes show a close relationship in lithology. The Pb isotope data suggest that the two complexes were originally one continuous body and experienced a similar geologic history since the early Proterozoic. Thus, we conclude that the Busan gneiss complex is either an extension of the basement rocks of the Kyongki Massif beneath the Okchon Belt or a tectonically emplaced piece of the Kyongki Massif. We reinterpret reported Rb-Sr muscovite and biotite ages for the Busan and Bagdalryeong gneiss complexes as the cooling age. The Rb-Sr muscovite ages were originally interpreted as the reset (or partially reset) ages during the Triassic metamorphism of the Okchon Belt (Cliff et al., 1985). Our alternative interpretation suggests that the Bagdalryeong gneiss complex was uplifted rapidly during the Jurassic, whereas the Busan gneiss complex was uplifted slowly since the late Permian. The fast uplift of the Bagdalryeong gneiss complex might have been related to the normal shear movement between the Kyongki Massif and the Okchon Belt (Ree et al., 1995).",
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N2 - The Busan gneiss complex is a unique body in the Okchon Belt in that it consists of high-grade gneisses surrounded by low-grade schists. In order to elucidate the origin of the Busan gneiss complex, we compared Pb isotope data from the complex with those from the nearby Bagdalryeong gneiss complex of the Kyongki Massif. The two complexes share common lithology, i.e., migmatitic gneiss and augen gneiss. The Pb data of whole rock and feldspar from the two complexes appear to form a single linear array in the 207Pb/ 204Pb-206Pb/204Pb diagram, corresponding to an age of 1932±65 (1σ) Ma. It represents either the formation age or the age of high-grade metamorphism, i.e., migmatization. The Th/U ratios calculated from the 208Pb/204Pb and 206Pb/ 204Pb data of both complexes show a close relationship in lithology. The Pb isotope data suggest that the two complexes were originally one continuous body and experienced a similar geologic history since the early Proterozoic. Thus, we conclude that the Busan gneiss complex is either an extension of the basement rocks of the Kyongki Massif beneath the Okchon Belt or a tectonically emplaced piece of the Kyongki Massif. We reinterpret reported Rb-Sr muscovite and biotite ages for the Busan and Bagdalryeong gneiss complexes as the cooling age. The Rb-Sr muscovite ages were originally interpreted as the reset (or partially reset) ages during the Triassic metamorphism of the Okchon Belt (Cliff et al., 1985). Our alternative interpretation suggests that the Bagdalryeong gneiss complex was uplifted rapidly during the Jurassic, whereas the Busan gneiss complex was uplifted slowly since the late Permian. The fast uplift of the Bagdalryeong gneiss complex might have been related to the normal shear movement between the Kyongki Massif and the Okchon Belt (Ree et al., 1995).

AB - The Busan gneiss complex is a unique body in the Okchon Belt in that it consists of high-grade gneisses surrounded by low-grade schists. In order to elucidate the origin of the Busan gneiss complex, we compared Pb isotope data from the complex with those from the nearby Bagdalryeong gneiss complex of the Kyongki Massif. The two complexes share common lithology, i.e., migmatitic gneiss and augen gneiss. The Pb data of whole rock and feldspar from the two complexes appear to form a single linear array in the 207Pb/ 204Pb-206Pb/204Pb diagram, corresponding to an age of 1932±65 (1σ) Ma. It represents either the formation age or the age of high-grade metamorphism, i.e., migmatization. The Th/U ratios calculated from the 208Pb/204Pb and 206Pb/ 204Pb data of both complexes show a close relationship in lithology. The Pb isotope data suggest that the two complexes were originally one continuous body and experienced a similar geologic history since the early Proterozoic. Thus, we conclude that the Busan gneiss complex is either an extension of the basement rocks of the Kyongki Massif beneath the Okchon Belt or a tectonically emplaced piece of the Kyongki Massif. We reinterpret reported Rb-Sr muscovite and biotite ages for the Busan and Bagdalryeong gneiss complexes as the cooling age. The Rb-Sr muscovite ages were originally interpreted as the reset (or partially reset) ages during the Triassic metamorphism of the Okchon Belt (Cliff et al., 1985). Our alternative interpretation suggests that the Bagdalryeong gneiss complex was uplifted rapidly during the Jurassic, whereas the Busan gneiss complex was uplifted slowly since the late Permian. The fast uplift of the Bagdalryeong gneiss complex might have been related to the normal shear movement between the Kyongki Massif and the Okchon Belt (Ree et al., 1995).

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