Strain patterns, décollement and incipient sagducted greenstone terrains in the Archaean Dharwar craton (south India)

doi:10.1016/0191-8141(96)00031-4

Journal of Structural Geology

Volume 18, Issue 8, August 1996, Pages 991-999, 1001-1004

https://doi.org/10.1016/0191-8141(96)00031-4 Get rights and content

Abstract

The Archaean Dharwar craton is characterized by two greenstone successions: the > 3 Ga Sargur Group and the 3.0–2.5 Ga Dharwar Supergroup. Examples of both successions are described from the region of Jayachamarajapura where they are also distinguished by different tectonic patterns. The younger greenstones have undergone only minor deformation and are only slightly metamorphosed and so provide a good case study of the relative behavior of greenstones in relation to their granite-gneiss country rocks. A detailed structural analysis indicates two strain fields associated with two deformational episodes: D₁ and D₂. The D₁ episode produced dome-and-basin structures and affected merely the older greenstones and the gneisses. The mapped strain field is compatible with the hypothesis that it is associated with the development of diapiric-type gravitational instabilities. The D₂ episode affects only the younger greenstone belt, which has the overall geometry of a complex syncline. It is discordant over a complex of gneisses and older greenstones that was deformed during the D₁ episode. The base of the discordant cover sequence is tectonized and constitutes a décollement surface. Kinematic criteria at this surface have opposite sense and converge towards the belt axis. These structural features are interpreted in terms of progressive deformation compatible with the incipient development of a sagducting trough.

These results are consistent with those obtained from other parts of the craton, where the tectonic evolution appears to reflect mainly relative vertical displacements facilitated by the reheating of continental crust during two major Archaean tectonometamorphic episodes.

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Citation Excerpt :
Most crystalline domes are frequently fringed by the occurrences of high-temperature (HT) metamorphic rocks, whereas greenschist facies mineral assemblages are only present in the keels and schist belts far from the domes. There are many examples in Archean terrains of domes that clearly represent inliers of older basement rocks predating the deposition of sedimentary and volcanic units (the greenstones) preserved in the keels (Chardon and Choukroune 1996). In other Archean provinces there are many examples of domes entirely represented by more or less foliated magmatic rocks that intrude the greenstone keels (Parmenter et al., 2006 and references therein).
New petrostructural data are presented from the southeastern Quadrilátero Ferrífero, a distinct polyorogenic domain of the São Francisco Craton characterized by granite-gneiss domes and keel structures. The Minas Supergroup of Siderian age that hosts a huge volume of ferriferous sediments was deposited on the flat and eroded surface of the Archean basement. The domes of Archean gneisses and granites represent semi-rigid extrusions around which the Minas Supergroup accumulated in deep synclines with common triple junctions. This study focuses first on the petro-structural context of low-pressure thermal aureoles observed towards the dome margins. Pressure-temperature estimates on these mineral assemblages indicate nearly static burial to ≥ 10 km depths of the Minas Supergroup cover, followed by decompression and heating during the intrusion of pegmatites and granitoids of late Rhyacian age in basement and cover. The Archean basement and the thermal aureoles were severely overprinted by synkinematic greenschist facies metamorphism portrayed by chloritoid, chlorite, pyrophyllite, kyanite, phengitic mica and secondary biotite. This deep greenschist facies metamorphism (T ca. 420°C and P = 0.4 to 0.45 GPa) is regionally observed in all units from the domes and the keels ranging in age from Archean to Ediacaran. It is concluded that this major tectono-metamorphic event relates to tectonic burial of the southern Quadrilatero Ferrifero below the west-verging nappes of the Araçuaí belt during the Early Paleozoic, as documented by 40Ar/39Ar ages of 490-485 Ma obtained on syn-kinematic metamorphic micas [Chauvet et al., 2001]. It is proposed that building up of the dome and keel tectonic style is first a consequence of the high-density contrast estimated around 0.5 g/cm₃ between the crystalline basement and the Minas Supergroup, the final architecture being achieved during the Cambro-Ordovician stage of the E-W Late Neoproterozoic collision.

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^∗: Present address: CEREGE, Université d'Aix Marseille 3, Domaine du petit Arbois, 13545 Aix-en-Provence Cedex 4, France.

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Strain patterns, décollement and incipient sagducted greenstone terrains in the Archaean Dharwar craton (south India)

Abstract

France. J. Struct. Geol.

J. Struct. Geol.

Earth Planet. Sci. Lett.

Precambrian Res.

J. Struct. Geol.

Tectonophysics

J. Struct. Geol.

Tectonophysics

Tectonophysics

Earth Sci. Rev.

Precambrian Res.

Precambrian Res.

J. Struct. Geol.

Tectonophysics

Geochim. cosmochim. Acta

Precambrian Res.

Tectonophysics

Tectonophysics

Precambrian Res.

Precambrian tectonic environments

A. Rev. Earth Planet Sci.

A reappraisal of some aspects of Precambrian shield geology

Bull. geol. Soc. Am.

3. 360 My old gneisses from the south Indian craton

Nature, Lond.

Orientations préfèr-entielles du quartz et orthogneissification progressive en régime cisaillant: l'exemple du cisaillement sudarmoricain

Bull. Mineral.

Horizontal tectonic interaction of an Archean gneiss belt and green-stones, Pilbara block, Western Australia

Geology

Evolution structurale et métamorphique de la croûte continentale Achéenne (Craton de Dharwar, Inde du Sud)

Mém. Géosciences-Rennes

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Bull. Soc. geol. Fr.

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Structural and metamorphic relations between Sargur and Dharwar supracrustal rocks and Peninsular gneiss in Central Karnataka

J. geol. Soc. India

Facies distributions and structures of a Dharwar volcanosedimentary basin: evidence for late Archaean transpression in southern India?

J. geol. Soc. Lond.

A comparative study of tectonic fabrics and deformation mechanisms in Dharwar grits and phyllites and Sargur quartzites on the west of the Chitradurga supracrustal belt, Karnataka

J. geol. Soc. India

Soft lithosphere during periods of Archean crustal growth or crustal reworking

Spec. Publs. geol. Soc. Lond.

Gravity induced folding off a gneiss dome complex, Rincon Mountains, Arizona

Bull. geol. Soc. Am.

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Geology

A shear-zone model for the structural evolution of metamorphic core complexes in southeastern Arizona

Spec. Publs. geol. Soc. Lond.

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J. Geol.

On the symmetry principle and the deformation ellipsoid

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SHRIMP U-Pb geochronology of the Closepet granite and Peninsular gneisses, Karnataka, South of India

J. geol. Soc. India

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Can. J. Earth Sci.

Ductile crust exhumation and extensional detachments in the central Aegean (Cyclades and Evvia islands)

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Science

Greenstone belts as ancient marginal basins or ensialic rift zones

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