Geochronology of Neoarchaean granitoids of the NW eastern Dharwar craton: implications for crust formation

Abstract

The Neoarchaean Era is characterized by large preserved record of continental crust formation. Yet the actual mechanism(s) of Neoarchaean crustal growth remains controversial. In the northwestern part of the eastern Dharwar craton (EDC) granitoid magmatism started at 2.68 Ga with gneissic granodiorites showing intermediate character between sanukitoid and tonalite–trondhjemite–granodiorite (TTG). This was followed by intrusion of transitional (large-ion lithophile element-enriched) TTGs at 2.58 Ga. Finally 2.53–2.52 Ga sanukitoid and Closepet-type magmatism and intrusion of K-rich leucogranites mark the cratonization in the area. These granitoids mostly display initial negative εNd and Mesoarchaean depleted mantle model ages, suggesting presence of older crust in the area. Available data show that most of the Neoarchaean sodic granitoids in the EDC are transitional TTGs demonstrating the importance of reworking of older crust. It is suggested that the various c. 2.7 Ga greenstone mafic–ultramafic volcanic rocks of EDC formed in oceanic arcs and plateaus which accreted to form continental margin environment. Subsequent 2.7–2.51 Ga granitoid magmatism involved juvenile addition of crust as well as reworking of felsic crust forming transitional TTGs, sanukitoids and K-rich leucogranites. Microcratons were possibly the source of older crustal signatures and their accretion appears to be one of the important processes of Neoarchaean crustal growth globally.Supplementary material: Analytical techniques are available at https://doi.org/10.6084/m9.figshare.c.3470724

Archaean granitoids: an overview and significance from a tectonic perspective

“…Archaean calc-alkaline sanukitoid granitoids that appeared in the geological record between 3.0 and 2.5 Ga are related to a source in an enriched subcontinental lithospheric mantle, thus indicating the existence of an enriched mantle source for granitoid magmatism since that time. Several contributions from Karelia and the Indian Shield (Dey et al 2016;Heilimo et al 2016;Joshi et al 2016;Mikkola et al 2016;Ramiz & Mondal 2016) find evidence for a long-or short-lived enriched mantle source below the cratons (western Karelia, Bundkelkhand and eastern Dharwar), as well as for subsequent or simultaneous mantle and crust melting. Metamorphic studies of Hölttä et al (2016) provide further support for a collisional tectonic setting in the Karelia Province.…”

“…Dey et al (2016) present secondary ion mass spectrometry (SIMS) U-Pb zircon ages, as well as major and trace element data, for granitoids in the NW part of the craton. The granitoid magmatism involves both juvenile addition and reworking of felsic crust forming enriched TTGs.…”

“…The papers by Dey et al (2016), Heilimo et al (2016), Joshi et al (2016) and Mikkola et al (2016) point out the geochemical diversification of granitoids and related rocks in the Neoarchaean by presenting geochemical and geochronological results of rock types such as alkali-enriched gabbros and granitoids, sanukitoids, and Closepet-type granitoids, as well as a heterogeneous group of monzogranitic rocks.…”

Neoarchaean magmatism through arc and lithosphere melting: Evidence from eastern Dharwar Craton

“…The Dharwar Craton records magmatic activity dated over the time interval 3.4–2.5 Ga (Dey et al, ; Guitreau, Mukasa, Loudin, & Krishnan, ; Jayananda et al, , ; Jayananda, Chardon, Peucat, & Capdevila, , ; Radhakrishna & Naqvi, ). Depending on the nature of greenstone belts, the age of the surrounding granitoids, and the deformation and metamorphic patterns, the Dharwar Craton is divided into two blocks: (Figure , inset map) the western Dharwar craton (WDC) and the EDC (Fig ; Chadwick et al, ).…”

“…The eastern Dharwar Craton (EDC) is one of the largest preserved Neoarchaean cratonic terrains, with exceptionally fresh exposures that serve as a natural laboratory for studying Archaean rocks (Figure ). Various types of granitoid and volcanic rocks have been reported from the EDC, with geochronological data indicating that greenstone formation, granitic magmatism, accretion, and deformation occurred within 2.7–2.5 Ga (Chardon & Jayananda, ; Chardon, Jayananda, & Peucat, ; Dey et al, ; Jayananda et al, , ; Nutman, Chadwick, Krishna Rao, & Vasudev, ; Rogers, Kolb, Meyer, & Armstrong, ; Sarma, McNaughton, Belousova, Ram Mohan, & Fletcher, ). The origin of juvenile magmatism, mechanism of crustal reworking, and geodynamic setting of the Neoarchaean EDC is still an active research topic (Chadwick, Vasudev, & Hegde, , ; Chadwick, Vasudev, Hedge, & Nutman, ; Chardon et al, , ; Chardon & Jayananda, ; Jayananda et al, ).…”