Lithology and structure of the Grenville-aged (∼1.1 Ga) basement of Heimefrontfjella (East Antarctica) |
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Authors: | J Jacobs W Bauer G Spaeth R J Thomas K Weber |
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Institution: | Universit?t Bremen, FB5-Geowissenschaften, Postfach 330440, D-28334 Bremen, Germany Fax: +0421 218 3993 e-mail: jojacobs@geopol.uni-bremen.de, DE Lehr- und Forschungsgebiet Geologie, Endogene Dynamik der RWTH Aachen, Lochnerstr. 4–20, D-52056 Aachen, Germany, DE Council for Geoscience, P.O. Box 900, 3200 Pietermaritzburg, RSA, ZA Institut für Geologie und Dynamik der Lithosph?re, Goldschmidtstr. 3, D-37077 G?ttingen, Germany, DE
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Abstract: | The Heimefrontfjella mountains, Western Dronning Maud Land (East Antarctica), are dominantly composed of Grenville-aged (≈
1.1 Ga) rocks, which were reworked during the Pan -African orogeny at ≈500 Ma. Three discontinuity-bounded Grenville-aged
terranes have been recognized namely (from north to south) the Kottas, Sivorg and Vardeklettane terranes. The terranes contain
their own characteristic lithological assemblages, although each is made up of an early supracrustal sequence of metavolcanic
and/or metasedimentary gneisses, intruded by various (predominantly granitoid) suites. No older basement upon which the protoliths
of these older gneisses were deposited has been recognized. In each terrane the older layered gneisses were intruded by various
plutonic suites ranging in age from ≈ 1150 to ≈1000 Ma. The Vardeklettane terrane is characterized by abundant charnockites
and two-pyroxene granulite facies parageneses in metabasites, whereas the Sivorg and Kottas terranes were metamorphosed to
amphibolite facies grade. P-T estimates show that peak metamorphic conditions changed from ≈600°C at 8 kbar in the south,
to ≈700 °C at 4 kbar in the northern Sivorg terrane. Regional greenschist retrogression of high-grade assemblages may be of
Pan-African age. The Heimefrontfjella terranes were juxtaposed and pervasively deformed during a complex and protracted period
of E-W collision orogenesis in a transpressive regime at ≈ 1.1 Ga. This is manifest as early, gently dipping thrust-related
shear fabrics (D1), succeeded by the initiation of an important (D2) steep dextral shear zone (Heimefront shear zone, HSZ), during which the early fabrics and structures were steepened and
rotated in an anticlockwise sense. The HSZ is a curvilinear structure which changes from a dextral oblique strike-slip lateral
ramp in the north to a steep dip-slip frontal ramp in the south, where it forms the boundary between the Sivorg and Vardeklettane
terranes. The Pan-African event is manifested as discrete, low- to medium-temperature ductile to brittle shears (D3) and numerous K/Ar cooling ages. |
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Keywords: | East Antarctica Greenville Pan-African Rodinia Heimefrontfjella |
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