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Dating fault-generated pseudotachylytes: comparison of Ar-40/Ar-39 stepwise-heating, laser ablation and Rb-Sr microsampling analyses

Mueller, Wolfgang; Kelley, Shari K; Villa, Igor M

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Three different geochronological techniques (stepwise-heating, laser-ablation 40Ar/39Ar, Rb-Sr microsampling) have been evaluated for dating fault-generated pseudotachylytes sampled along the Periadriatic Fault System (PAF) of the Alps. Because pseudotachylytes are whole-rock systems composed of melt, clast and alteration phases, chemical control from both Ar isotopes (Cl/K, Ca/K ratios) and EMPA analyses is crucial for their discrimination. When applied to stepwise-heating 40Ar/39Ar analyses,...[Show more]

dc.contributor.authorMueller, Wolfgang
dc.contributor.authorKelley, Shari K
dc.contributor.authorVilla, Igor M
dc.date.accessioned2015-12-13T22:25:54Z
dc.identifier.issn0010-7999
dc.identifier.urihttp://hdl.handle.net/1885/73471
dc.description.abstractThree different geochronological techniques (stepwise-heating, laser-ablation 40Ar/39Ar, Rb-Sr microsampling) have been evaluated for dating fault-generated pseudotachylytes sampled along the Periadriatic Fault System (PAF) of the Alps. Because pseudotachylytes are whole-rock systems composed of melt, clast and alteration phases, chemical control from both Ar isotopes (Cl/K, Ca/K ratios) and EMPA analyses is crucial for their discrimination. When applied to stepwise-heating 40Ar/39Ar analyses, this approach yields accurate melt-related ages, even for complex age spectra. The spatial resolution of laser-ablation 40Ar/39Ar analyses is capable of contrasting melt, clast and alteration phases in situ, provided the clasts are not too fine grained, the latter of which results in integrated "mixed" ages without geological information. Elevated Cl/K and Ca/K ratios were found to be an invaluable indicator for the presence of clast admixture or inherited 40Ar. Due to incomplete isotopic resetting during frictional melting, Rb-Sr microsampling dating did not furnish geologically meaningful ages. On the basis of isotopic disequilibria among pseudotachylyte matrix phases, and independent Rb-Sr microsampling dating of cogenetic (ultra) mylonites, the concordant 40Ar/39Ar pseudotachylyte ages are interpreted as formation ages. The investigated pseudotachylytes altogether reveal a Cretaceous to Miocene history for the entire PAF, consistent with independent geological evidence. Individual faults, however, consistently reveal narrower intervals of enhanced activity lasting a few million years. Electronic supplementary material to this paper can be obtained by using the Springer LINK server at http://dx.doi.org/ 10.1007/s00410-002-0381-6.
dc.publisherSpringer
dc.sourceContributions to Mineralogy and Petrology
dc.subjectKeywords: argon-argon dating; dating method; faulting; geochemistry; geochronology; melting; pseudotachylite
dc.titleDating fault-generated pseudotachylytes: comparison of Ar-40/Ar-39 stepwise-heating, laser ablation and Rb-Sr microsampling analyses
dc.typeJournal article
local.description.notesImported from ARIES
local.description.refereedYes
local.identifier.citationvolume144
dc.date.issued2002
local.identifier.absfor040303 - Geochronology
local.identifier.ariespublicationMigratedxPub3705
local.type.statusPublished Version
local.contributor.affiliationMueller, Wolfgang, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationKelley, Shari K, New Mexico Bureau of Geology and Mineral Resources
local.contributor.affiliationVilla, Igor M, University of Bern
local.description.embargo2037-12-31
local.bibliographicCitation.issue1
local.bibliographicCitation.startpage57
local.bibliographicCitation.lastpage77
dc.date.updated2015-12-11T08:19:26Z
local.identifier.scopusID2-s2.0-0036819481
CollectionsANU Research Publications

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