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Argon release mechanisms and metamor...

Lo, Ching-Hua.

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Argon release mechanisms and metamorphic effects on the argon-40/argon-39 geochronology of rocks from Taiwan.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Argon release mechanisms and metamorphic effects on the argon-40/argon-39 geochronology of rocks from Taiwan./
Author:	Lo, Ching-Hua.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 1990,
Description:	282 p.
Notes:	Source: Dissertations Abstracts International, Volume: 52-10, Section: B.
Contained By:	Dissertations Abstracts International52-10B.
Subject:	Geology. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9104335
ISBN:	9781392596746

Argon release mechanisms and metamorphic effects on the argon-40/argon-39 geochronology of rocks from Taiwan.
Lo, Ching-Hua.

Argon release mechanisms and metamorphic effects on the argon-40/argon-39 geochronology of rocks from Taiwan. - Ann Arbor : ProQuest Dissertations & Theses, 1990 - 282 p.

Source: Dissertations Abstracts International, Volume: 52-10, Section: B.

Thesis (Ph.D.)--Princeton University, 1990.

This item must not be sold to any third party vendors.

Understanding the mechanisms of argon release from minerals is fundamental in order to interpret $\\sp{40}$Ar/$\\sp{39}$Ar dates in natural setting. In conjunction with detailed petrographic examinations, electron microscopy, X-ray powder diffractometry, and transmission electron microscopy and image analysis techniques, this study attempts to determine the mechanisms and kinetics of argon release from minerals during $\\sp{40}$Ar-$\\sp{39}$Ar in-vacuo heating and under natural metamorphic conditions, and also further expand the utility of the $\\sp{40}$Ar-$\\sp{39}$Ar dating technique, by using materials collected from the basement rocks of the Taiwan Mountain Belt and the Luzon Arc. When biotites are heated in-vacuo, the argon release mechanism is dominated by a reaction-enhanced loss which is closely related to the decomposition of the biotite structure at temperatures $\\geq$600$\\sp\\circ$C; at low temperatures ($<$600$\\sp\\circ$C), argon release is controlled mainly by volume diffusion. The diffusion process may also be significantly enhanced by pipe diffusion as a result of structural defects within the minerals. In the case of metamorphic reheating in the Taiwan Mountain Belt, argon release from minerals is primarily controlled by a thermally-activated volume-diffusion process associated with secondary recrystallization effects. The amount of argon lost from the minerals can be quantitatively predicted by a volume diffusion model coupled with a thermal model of the Taiwan Mountain Belt. The thermally-overpinted biotites in Taiwan commonly yield complicated internally discordant $\\sp{40}$Ar/$\\sp{39}$Ar age spectra, which were found to be caused by the simultaneous release of argon from the chlorite and biotite intercalations in the samples. An $\\sp{39}$Ar internal recoil model can best explain this disturbance, and can potentially be applied to explain discordant age spectra reported for other minerals. Volcanic rocks from the northern tip of the Luzon Arc yield flat age spectra over a substantial $\\sp{39}$Ar$\\sb{\\rm K}$ released, with some disturbances at the low- and high-temperature steps, which were mainly due to the presence of secondary alteration and inherited excess argon. Nevertheless, these are discernible by $\\sp{40}$Ar-$\\sp{39}$Ar step-heating technique. Experimental procedures may also add complications in dating altered volcanic rocks. In order to obtain reliable $\\sp{40}$Ar/$\\sp{39}$Ar plateau dates for such samples, it is necessary to bakeout at much lower temperatures and for longer times than previously thought.

ISBN: 9781392596746Subjects--Topical Terms:

516570
Geology.
Subjects--Index Terms:

China

Argon release mechanisms and metamorphic effects on the argon-40/argon-39 geochronology of rocks from Taiwan.
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100 1 $a Lo, Ching-Hua. $3 547222
245 1 0 $a Argon release mechanisms and metamorphic effects on the argon-40/argon-39 geochronology of rocks from Taiwan.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 1990
300 $a 282 p.
500 $a Source: Dissertations Abstracts International, Volume: 52-10, Section: B.
500 $a Publisher info.: Dissertation/Thesis.
502 $a Thesis (Ph.D.)--Princeton University, 1990.
506 $a This item must not be sold to any third party vendors.
506 $a This item must not be added to any third party search indexes.
520 $a Understanding the mechanisms of argon release from minerals is fundamental in order to interpret $\\sp{40}$Ar/$\\sp{39}$Ar dates in natural setting. In conjunction with detailed petrographic examinations, electron microscopy, X-ray powder diffractometry, and transmission electron microscopy and image analysis techniques, this study attempts to determine the mechanisms and kinetics of argon release from minerals during $\\sp{40}$Ar-$\\sp{39}$Ar in-vacuo heating and under natural metamorphic conditions, and also further expand the utility of the $\\sp{40}$Ar-$\\sp{39}$Ar dating technique, by using materials collected from the basement rocks of the Taiwan Mountain Belt and the Luzon Arc. When biotites are heated in-vacuo, the argon release mechanism is dominated by a reaction-enhanced loss which is closely related to the decomposition of the biotite structure at temperatures $\\geq$600$\\sp\\circ$C; at low temperatures ($<$600$\\sp\\circ$C), argon release is controlled mainly by volume diffusion. The diffusion process may also be significantly enhanced by pipe diffusion as a result of structural defects within the minerals. In the case of metamorphic reheating in the Taiwan Mountain Belt, argon release from minerals is primarily controlled by a thermally-activated volume-diffusion process associated with secondary recrystallization effects. The amount of argon lost from the minerals can be quantitatively predicted by a volume diffusion model coupled with a thermal model of the Taiwan Mountain Belt. The thermally-overpinted biotites in Taiwan commonly yield complicated internally discordant $\\sp{40}$Ar/$\\sp{39}$Ar age spectra, which were found to be caused by the simultaneous release of argon from the chlorite and biotite intercalations in the samples. An $\\sp{39}$Ar internal recoil model can best explain this disturbance, and can potentially be applied to explain discordant age spectra reported for other minerals. Volcanic rocks from the northern tip of the Luzon Arc yield flat age spectra over a substantial $\\sp{39}$Ar$\\sb{\\rm K}$ released, with some disturbances at the low- and high-temperature steps, which were mainly due to the presence of secondary alteration and inherited excess argon. Nevertheless, these are discernible by $\\sp{40}$Ar-$\\sp{39}$Ar step-heating technique. Experimental procedures may also add complications in dating altered volcanic rocks. In order to obtain reliable $\\sp{40}$Ar/$\\sp{39}$Ar plateau dates for such samples, it is necessary to bakeout at much lower temperatures and for longer times than previously thought.
590 $a School code: 0181.
650 4 $a Geology. $3 516570
653 $a China
690 $a 0372
710 2 $a Princeton University. $3 645579
773 0 $t Dissertations Abstracts International $g 52-10B.
790 $a 0181
791 $a Ph.D.
792 $a 1990
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9104335