Geochronological constraints on the Hartbees River Thrust and Augrabies Nappe: New insights into the assembly of the Mesoproterozoic Namaqua-Natal Province of Southern Africa

• The region around Augrabies in the Namaqua sector provides insights into the processes that formed the Namaqua-Natal tectonic Province. Progressive ductile shear deformation during the long lasting Namaqua Orogeny was coeval with the global Grenvillian Orogeny. The Mesoproterozoic Namaqua-Natal Province is composed of severely deformed and metamorphosed rocks in terranes bounded by major thrust and shear zones. The interpreted research results deal with events around the Hartbees River Thrust, a suture zone where the granulite grade Grunau (Kakamas) terrane was overthrust onto the amphibolite grade Bladgrond (Bushmanland) terrane. The series of distinct deformation stages D-1-D-6 that have been identified during previous research in the western regions of the Namaqua sector, is also discernible in the study region around Augrabies. Microbeam geochronological techniques were used to date zircons from four samples of a granitic rock (the Karama'am Augen Gneiss) intrusive into the Hartbees River Thrust zone, and of a sample of granite (the Augrabies Granite) from the core of a large allochthonous sheath fold nappe in the Grunau terrane. The mean crystallisation age of the Karama'am intrusive is 1108 +/- 4 Ma and of the Augrabies Granite 1168 +/- 6 Ma. The sheath fold core of the latter granite is enclosed in the sheetlike Rooipad Granite (Riemvasmaak Granite) previously determined to be 1155 +/- 7 Ma. Crustal residence times deduced from Lu-Hf isotopic compositions of zircon cores and xenocrysts, cluster around 1710 Ma for the Augrabies Granite and about 200 Ma older for the Karama'am Granite Gneiss (with the oldest date at 2069 Ma). Collectively the available data enable reconstruction of the sequence of Namaqua Orogeny deformation stages: terrane assembly (D-1) at similar to 1195 Ma with metamorphism at 1191 +/- 12 Ma, pervasive folding and thrusting (D-2) at 1168 +/- 6 Ma, formation of major sheath and coaxial folds (D-3) at 1155 +/- 7 Ma, late open folds (D-4) at 1090 +/- 16 and a late metamorphism (coeval with major shear zones D-5-D-6?) at 1018 +/- 11 to 1024 +/- 14 Ma. (C) 2015 Elsevier B.V. All rights reserved.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences (hsv//eng)

Nyckelord

Namaqua-Natal Province

Hartbees River Thrust

Microbeam zircon dating

Augrabies Granite Gneiss

OKIEP COPPER DISTRICT

METAMORPHIC COMPLEX

AGGENEYS TERRANE

MOBILE

BELT

T METAMORPHISM

LU-HF

EVOLUTION

WESTERN

ZIRCON

RODINIA

Geosciences

Multidisciplinary

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