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Time constraints for Mesoproterozoic upper amphibolite facies metamorphism in NW Namibia: a multi-isotopic approach.

Seth, Barbara; Armstrong, Richard; Buttner, Annett; Villa, Igor M

Description

This study presents the chronological evolution of the upper amphibolite facies Orue Unit in NW Namibia. Metasedimentary and meta-igneous rocks of the Orue Unit were investigated using the Pb-Pb stepwise leaching technique on garnet and rutile, U-Pb multi-grain analysis on rutile, Sm-Nd-Lu-Hf leaching technique on garnet, SHRIMP analysis on zircon and Ar-Ar dating on amphibole. Each of these techniques pertains to different processes that occurred before, during, or after the metamorphic peak....[Show more]

dc.contributor.authorSeth, Barbara
dc.contributor.authorArmstrong, Richard
dc.contributor.authorButtner, Annett
dc.contributor.authorVilla, Igor M
dc.date.accessioned2015-12-13T22:43:26Z
dc.identifier.issn0012-821X
dc.identifier.urihttp://hdl.handle.net/1885/79204
dc.description.abstractThis study presents the chronological evolution of the upper amphibolite facies Orue Unit in NW Namibia. Metasedimentary and meta-igneous rocks of the Orue Unit were investigated using the Pb-Pb stepwise leaching technique on garnet and rutile, U-Pb multi-grain analysis on rutile, Sm-Nd-Lu-Hf leaching technique on garnet, SHRIMP analysis on zircon and Ar-Ar dating on amphibole. Each of these techniques pertains to different processes that occurred before, during, or after the metamorphic peak. Our age data can be integrated with petrological constraints to provide a more complete understanding of the metamorphic cycle. Our pre-peak metamorphic zircon ages, peak metamorphic garnet ages and peak to late peak metamorphic amphibole 39Ar-40Ar ages bracket the upper amphibolite facies metamorphic event including hydration or dehydration processes into a time span of only ca. 20 Ma. The age data obtained by peak metamorphic mineral analyses cluster around 1340-1320 Ma. Based on age data and field observation, we interpret the upper amphibolite facies metamorphism as a large-scale regional mid-crustal event. Spot analyses of inherited zircon cores obtained by SHRIMP reflect the sedimentary origin of the respective rocks of the Orue Unit and derivation from Palaeoproterozoic protoliths. The metamorphic rocks south of the anorthositic Kunene Intrusive Complex (KIC) have previously been ascribed to the Palaeoproterozoic Epupa Complex at the SW margin of the Congo craton and were thus thought to be older than the Mesoproterozoic KIC. Our data show that the high-grade metamorphic overprint took place 30-50 Ma after emplacement of the KIC. Rutile growth ages of 1248 Ma in one sample reflect fluid activity which seems to be a local phenomenon since there is no other evidence of geological activity throughout the Orue Unit at that time. The rutile ages predate the emplacement of satellite intrusions in that area by 30 Ma and there is no causal relation between these two events.
dc.publisherElsevier
dc.sourceEarth and Planetary Science Letters
dc.subjectKeywords: Age data; Kunene intrusive complex (KIC); Mesoprotrozoic; Palaeoproterozoic epupa complex; Dehydration; Garnets; Geophysical prospecting; Hydration; Igneous rocks; Leaching; Petrology; Zircon; Metamorphic rocks; amphibole; argon-argon dating; geochronolog Geochronology; High-grade metamorphism; Mesoproterozoic; Namibia; Upper amphibolite facies
dc.titleTime constraints for Mesoproterozoic upper amphibolite facies metamorphism in NW Namibia: a multi-isotopic approach.
dc.typeJournal article
local.description.notesImported from ARIES
local.description.refereedYes
local.identifier.citationvolume230
dc.date.issued2005
local.identifier.absfor040203 - Isotope Geochemistry
local.identifier.ariespublicationMigratedxPub7694
local.type.statusPublished Version
local.contributor.affiliationSeth, Barbara, Royal Holloway University of London
local.contributor.affiliationArmstrong, Richard, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationButtner, Annett, University of Berne
local.contributor.affiliationVilla, Igor M, University of Bern
local.description.embargo2037-12-31
local.bibliographicCitation.startpage355
local.bibliographicCitation.lastpage378
local.identifier.doi10.1016/j.epsl.2004.11.022
dc.date.updated2015-12-11T10:12:24Z
local.identifier.scopusID2-s2.0-12744273647
CollectionsANU Research Publications

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