Petrology and 40Ar–39Ar dating of shear zones in the Lanterman Range (northern Victoria Land, Antarctica): implications for metamorphic and temporal evolution at terrane boundaries |
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| Authors: | L Crispini G Di Vincenzo R Palmeri |
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| Institution: | (1) Dipartimento per lo studio del Territorio e delle sue Risorse, Università di Genova, Genova, Italy;(2) Istituto di Geoscienze e Georisorse – CNR, Pisa, Italy;(3) Museo Nazionale dell’Antartide, Università di Siena, Siena, Italy |
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| Abstract: | Summary The Lanterman Fault Zone, a major terrane boundary in northern Victoria Land, displays a polyphase structural evolution. After
west-over-east thrusting, it experienced sinistral strike-slip shearing. Sheared metabasites from the Wilson Terrane (inboard
terrane) preserve a record of retrograde metamorphic evolution. Shearing took place under amphibolite-facies metamorphic conditions
(roughly comparable to those reached during regional metamorphism) which later evolved to greenschist-facies conditions. In
contrast, the Bowers Terrane (outboard terrane) preserves a prograde metamorphic evolution which developed from greenschist-facies
to amphibolite-facies metamorphism during shearing, followed by greenschist-facies metamorphism during the late deformational
stages. Laser step-heating 40Ar–39Ar analyses of syn-shear amphibolite-facies amphiboles yielded ages of 480–460 Ma, in agreement with a ∼480-Ma age obtained
from a biotite aligned along the mylonitic foliation. These ages are younger than those (∼492 to ∼495 Ma) obtained from pre-shear
amphibole relics linked to regional metamorphism of the Wilson Terrane. Results attribute the structural and metamorphic reworking
during shearing to the late stages of the Cambrian-Ordovician Ross Orogeny and to the Middle-Late Ordovician probably in relation
to the beginning of deformation in the Lachlan Orogen, thus precluding any appreciable impact of the Devonian-Carboniferous
Borchgrevink event in the study area. |
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