Syntectonic granite emplacement at different structural levels: The Closepet granite, South India

The Closepet granite, in South India, is a large (400 km long but only 30 km wide), elongate, Late Archaean granitic body. Structural levels from deep crust to upper levels crop out, as evidenced by a shallowing of paleo-depths from north to south all along the Closepet granite. This allows the study of the emplacement of the same granitic body at various crustal levels. Four zones have been identified: a root zone, where magmas are collected in active shear zones; a transfer zone, featuring large-scale magma ascent and crystal-liquid partitioning in the granitic 'mush'; a 'gap', where the mush was filtered, allowing only the liquids to rise; shallow intrusions, filled with this liquid. The Closepet granite was emplaced syntectonically. Field work and anisotropy of magnetic susceptibility allowed documentation of steep foliations with subhorizontal lineations, both in the root and transfer zones and in the shallow intrusions. Remote sensing evidenced a network of shear zones bounding the Closepet granite. In the porphyritic root and transfer zones, magmas cooled slowly, thus developing strong fabrics during large-scale dextral shearing. Ascent of residual liquids amidst the crystallizing solid framework was not recorded in the fabrics. However, these liquids were channelised through the gap and infilled the homogeneous shallow intrusions, where rapid cooling only permitted the development of feint, although wholly consistent, fabrics. © 2002 Elsevier Science Ltd. All rights reserved

Felsic crust development in the Kaapvaal Craton, South Africa: A reference sample collection to investigate a billion years of geological history

The crust of the Kaapvaal craton accreted throughout the Archaean over nearly 1 billion years. It provides a unique example of the various geological processes that shape Earth's continental crust, and is illustrated by a reference collection of granitoids and mafic rocks (SWASA collection). This sample collection is fully characterised in term of age, major and trace elements, and documents the following multistage history of the craton. In the Barberton area, the initial stages of accretion (stage B·I, > 3.33 Ga and B.II, 3.28—3.21 Ga) correspond to the formation of a sodic (TTG) crust extracted from a near-chondritic reservoir. Stage B.III (ca. 3.1 Ga) corresponds to reworking of this crust, either through intracrustal melting, or via recycling of some material into the mantle and melting of this enriched mantle. Stage B.IV (2.85—2.7 Ga) corresponds to the emplacement of small, discrete plutons involving limited intracrustal reworking. The Northern Kaapvaal craton corresponds to a mobile belt flanking the Barberton cratonic core to the North. Stage NK·I (> 3.1 Ga) resembles stages B·I and B.II: formation of a TTG crust from a chondritic reservoir. In contrast, stage NK.II. (2.97–2.88 Ga) witnesses probable rifting of a cratonic fragment and formation of greenstone basins as well as a new generation of TTGs with both the mafic and felsic magmatism extracted from an isotopically depleted mantle (super-chondritic) reservoir. Intra-crustal reworking dominates stage NK.III (2.88–2.71 Ga), whereas sanukitoids and related granites, involving a mantle contaminated by recycled crustal material, are common during stage NK.IV (ca. 2.67 Ga)

The multiple ways of recycling Archaean crust: A case study from the ca. 3.1 Ga granitoids from the Barberton Greenstone Belt, South Africa

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