An 40Ar-39Ar investigation of high-pressure metamorphism and the retrogressive history of mafic eclogites from the Lanterman Range (Antarctica): evidence against a simple temperature control on argon transport in amphibole (Articolo in rivista)

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  • An 40Ar-39Ar investigation of high-pressure metamorphism and the retrogressive history of mafic eclogites from the Lanterman Range (Antarctica): evidence against a simple temperature control on argon transport in amphibole (Articolo in rivista) (literal)
Anno
  • 2001-01-01T00:00:00+01:00 (literal)
Alternative label
  • Di Vincenzo G. , Palmeri R. (2001)
    An 40Ar-39Ar investigation of high-pressure metamorphism and the retrogressive history of mafic eclogites from the Lanterman Range (Antarctica): evidence against a simple temperature control on argon transport in amphibole
    in Contributions to mineralogy and petrology
    (literal)
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  • Di Vincenzo G. , Palmeri R. (literal)
Pagina inizio
  • 15 (literal)
Pagina fine
  • 35 (literal)
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  • Results support the interpretation that the different argon ages recorded diachronous amphibole growth at different crustal levels during exhumation. Regionally, this indicates that there was about a 10 Ma interval between the eclogite facies stage (at >- 1.5 GPa) and the Ca amphibole-hydration forming reaction (at 0.3 - 0.5 GPa); this translates into an average exhumation rate of 3-4 km/Myr. (literal)
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  • 141 (literal)
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  • Impact Factor 2,534 (literal)
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  • This study has important general implications for the interpretation of argon data from amphibole of metamorphic rocks. Firstly, care must be taken in deriving cooling histories from a small sample set, especially when the role of additional processes promoting recrystallization (e.g. fluid circulation) which are faster than simple volume diffusion, is neglected. Secondly, results show that fluids, along with the exhumation history, may strongly influence the behaviour of argon in metamorphic rocks. In metamorphic rocks which experienced fast exhumation and cooling, and suffered an essentially anhydrous evolution, different argon domains on a millimetre scale, even within the same mineral grain can be preserved. This study confirms other documented findings that argon diffusion rates in metamorphic amphiboles at their common formation temperature (i.e. under amphibolite-facies metamorphism) are very low and that metamorphic amphibole records growth age instead of cooling. (literal)
Note
  • ISI Web of Science (WOS) (literal)
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  • G. Di Vincenzo a), R. Palmeri b). a)CNR- IGG, via Moruzzi, 1, 56124 Pisa, Italy; b) Museo Nazionale dell'Antartide - Sezione di Scienze della Terra, Universit√† di Siena, via Laterina, 8, 53100 Siena, Italy (literal)
Titolo
  • An 40Ar-39Ar investigation of high-pressure metamorphism and the retrogressive history of mafic eclogites from the Lanterman Range (Antarctica): evidence against a simple temperature control on argon transport in amphibole (literal)
Abstract
  • Mafic eclogites from a restricted area in the Lanterman Range (Antarctica) retrogressed variably under amphibolite facies metamorphism. Assemblages range from well-preserved eclogite, with minor Na-Ca amphibole, to strongly retrogressed ones with extensive development of Ca amphibole. 40Ar-39Ar furnace step-heating experiments on the different amphiboles yield ages from ca. 498 to 490 Ma, and the greater the amphibolite retrogression, the younger the age. 40Ar-39Ar laser analyses on rock chips from a well-preserved eclogite and a slightly retrogressed one reveal the presence of an excess argon component. Whereas excess argon is invariably present in garnet and clinopyroxene developed under HP stage, it is heterogeneously distributed in amphibole on a millimetre scale. Results indicate that excess argon was incorporated during HP metamorphism; this component was then lost during retrogression, while a change in composition of ambient argon to atmospheric argon occurred. New and previously published data suggest that the oldest Na-Ca amphibole age is reliable and not an artefact due to the incorporation of excess argon. The variably retrogressed eclogites are thought to derive from different parts of the enclosing metasedimentary rocks that were variably invaded by fluids during amphibolite facies metamorphism. Thus the circulation of fluids promoting (re)crystallisation, and not temperature, was the main process controlling the rate of argon transport in the studied eclogites. (literal)
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