Rb-Sr isotopic study of the Hwacheon granite in northern Gyeonggi massif, Korea: A ease of spurious Rb-Sr whole rock age

Sung Tack Kwon, C. S. Cheong, H. Sagong

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

The Yonghwasan pluton of the Hwacheon granite intruding the Preeambrian metamorphic rocks of the northern Gyeonggi massif gives two apparent Rb-Sr whole rock isochrons depending on lithology: 177±11 Ma with an initial 87Sr/86Sr of 0.71538±0.00031 for mica granite and 134±10Ma with an initial 87Sr/86Sr of 0.72183±0.00096 for garnet two-mica granite. However, the whole rock age for the garnet two-mica granite is much younger than mineral ages: Rb-Sr biotite (146.2±2.2 Ma) and muscovite (160.2±1.6Ma), and reported CHIME monazite and K-Ar muscovite. Circumstantial evidences suggest that the young whole rock isochron may be the result from fortuitous alignment of data due to assimilation of country rocks, and thus meaningless, rather than resetting of whole rock Sr isotope ratios by later events such as post-emplacement heating and fluid infiltration. Considering the above, the best Rb-Sr whole rock age of the Yonghwasan pluton is estimated to be 172.0±6.8 Ma. The isotopic ages of this and previous studies for the garnet two-mica granite form a near linear cooling curve with a cooling rate of about 14.5°C/Ma.

Original languageEnglish
Pages (from-to)137-143
Number of pages7
JournalGeosciences Journal
Volume10
Issue number2
DOIs
Publication statusPublished - 2006 Jul 21

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granite
mica
garnet
rock
muscovite
pluton
cooling
resetting
monazite
country rock
metamorphic rock
biotite
lithology
emplacement
infiltration
isotope
heating
fluid
mineral
young

All Science Journal Classification (ASJC) codes

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

Cite this

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title = "Rb-Sr isotopic study of the Hwacheon granite in northern Gyeonggi massif, Korea: A ease of spurious Rb-Sr whole rock age",
abstract = "The Yonghwasan pluton of the Hwacheon granite intruding the Preeambrian metamorphic rocks of the northern Gyeonggi massif gives two apparent Rb-Sr whole rock isochrons depending on lithology: 177±11 Ma with an initial 87Sr/86Sr of 0.71538±0.00031 for mica granite and 134±10Ma with an initial 87Sr/86Sr of 0.72183±0.00096 for garnet two-mica granite. However, the whole rock age for the garnet two-mica granite is much younger than mineral ages: Rb-Sr biotite (146.2±2.2 Ma) and muscovite (160.2±1.6Ma), and reported CHIME monazite and K-Ar muscovite. Circumstantial evidences suggest that the young whole rock isochron may be the result from fortuitous alignment of data due to assimilation of country rocks, and thus meaningless, rather than resetting of whole rock Sr isotope ratios by later events such as post-emplacement heating and fluid infiltration. Considering the above, the best Rb-Sr whole rock age of the Yonghwasan pluton is estimated to be 172.0±6.8 Ma. The isotopic ages of this and previous studies for the garnet two-mica granite form a near linear cooling curve with a cooling rate of about 14.5°C/Ma.",
author = "Kwon, {Sung Tack} and Cheong, {C. S.} and H. Sagong",
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Rb-Sr isotopic study of the Hwacheon granite in northern Gyeonggi massif, Korea : A ease of spurious Rb-Sr whole rock age. / Kwon, Sung Tack; Cheong, C. S.; Sagong, H.

In: Geosciences Journal, Vol. 10, No. 2, 21.07.2006, p. 137-143.

Research output: Contribution to journalArticle

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AB - The Yonghwasan pluton of the Hwacheon granite intruding the Preeambrian metamorphic rocks of the northern Gyeonggi massif gives two apparent Rb-Sr whole rock isochrons depending on lithology: 177±11 Ma with an initial 87Sr/86Sr of 0.71538±0.00031 for mica granite and 134±10Ma with an initial 87Sr/86Sr of 0.72183±0.00096 for garnet two-mica granite. However, the whole rock age for the garnet two-mica granite is much younger than mineral ages: Rb-Sr biotite (146.2±2.2 Ma) and muscovite (160.2±1.6Ma), and reported CHIME monazite and K-Ar muscovite. Circumstantial evidences suggest that the young whole rock isochron may be the result from fortuitous alignment of data due to assimilation of country rocks, and thus meaningless, rather than resetting of whole rock Sr isotope ratios by later events such as post-emplacement heating and fluid infiltration. Considering the above, the best Rb-Sr whole rock age of the Yonghwasan pluton is estimated to be 172.0±6.8 Ma. The isotopic ages of this and previous studies for the garnet two-mica granite form a near linear cooling curve with a cooling rate of about 14.5°C/Ma.

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