Abstract Granitoids form the dominant component of Archean cratons. They are generated by partial melting of diverse crustal and mantle sources and subsequent differentiation of the primary magmas, and are formed through a variety of geodynamic processes. Granitoids, therefore, are important archives for early Earth lithospheric evolution. Peninsular India comprises five cratonic blocks bordered by mobile belts. The cratons that stabilized during the Paleoarchean–Mesoarchean (Singhbhum and Western Dharwar) recorded mostly diapirism or sagduction tectonics. Conversely, cratons that stabilized during the late Neoarchean (Eastern Dharwar, Bundelkhand, Bastar and Aravalli) show evidence consistent with terrane accretion–collision in a convergent setting. Thus, the Indian cratons provide testimony to a transition from a dominantly pre-plate tectonic regime in the Paleoarchean–Mesoarchean to a plate-tectonic-like regime in the late Neoarchean. Despite this diversity, all five cratons had a similar petrological evolution with a long period (250–850 myr) of episodic tonalite–trondhjemite–granodiorite (TTG) magmatism followed by a shorter period (30–100 myr) of granitoid diversification (sanukitoid, K-rich anatectic granite and A-type granite) with signatures of input from both mantle and crust. The contributions of this Special Publication cover diverse granitoid-related themes, highlighting the potential of Indian cratons in addressing global issues of Archean crustal evolution.

Abstract Many Paleoarchean cratons display a gradual change from early sodic tonalite–trondhjemite–granodiorite magmatism to late K-rich granitoid magmatism; the geodynamic significance of this change is debatable though. This contribution presents field, geochemical and zircon U–Pb age and Hf isotope results of four different 3.32–3.25 Ga granitoid bodies from the northern part of Singhbhum Craton to investigate their petrogenesis and role in crustal evolution. The granitoids range in composition from tonalites to trondhjemites, derived from intracrustal melting at low- to medium-pressure conditions. The source was mainly low-K mafic rock. The granitoids show intrasuite fractional crystallization. These sodic granitoids represent the last stage of granitoid magmatism in the Singhbhum Craton which formed contemporaneously with K-rich granitoids occurring in other parts of the craton. This fact suggests that, contrary to the popular notion (of only potassic granitoids), both sodic and potassic granitoids could form at the terminal phase of cratonization, implying reworking of heterogeneous (mafic to tonalite) crust. A combination of evidence from geochemical data, secular change in granitoid composition, structural pattern and rock association of the Singhbhum Craton reflects that recurring mantle plume-related mafic–ultramafic magma emplacement in an oceanic plateau setting and attendant crustal melting can explain the Paleoarchean crustal evolution pattern.

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

Abstract The Proterozoic Kaladgi–Badami and Bhima basins are intracratonic basins occurring over the Archaean Dharwar craton. The Kaladgi–Badami Basin contains arenites, shales and carbonates with minor cherts and conglomerates deposited in continental, transitional and shallow-marine environments presumably during the late Palaeoproterozoic/Mesoproterozoic to Neoproterozoic. The lower part of the succession (Bagalkot Group) is deformed into east–west-trending elongated doubly plunging synclines and anticlines. The upper part of the succession (Badami Group) is undeformed and unconformably overlies the lower part. The evolution of the Kaladgi–Badami Basin was controlled by movements along east–west-trending normal faults under an extensional stress regime. The Bhima Basin hosts mainly limestones with subordinate arenites and shales deposited in fluvial, deltaic and tidal flat environments possibly during the Neoproterozoic. These sediments are undeformed except along faults with significant strike-slip components. The basin is exposed in narrow strips arranged in an en echelon pattern and appears to be a pull-apart basin. Inadequate data exist on the age of the basin fills, the deep basinal architecture, subsidence history and tectonic controls for both of the basins. Future research may be directed towards these aspects which will have wide implications for understanding intracratonic basin formation, reconstructing Proterozoic supercontinents and studying the evolution of the atmosphere and primitive life forms.

Abstract Field and geochemical studies combined with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating set important constraints on the timing and petrogenesis of volcanic rocks of the Neoarchaean Kadiri greenstone belt and the mechanism of crust formation in the eastern Dharwar craton (EDC). The volcanic rocks are divided into three suites: tholeiitic basalts, calc-alkaline high-Mg# andesites and dominant dacites–rhyolites. The basalts (pillowed in places) show flat rare earth element (REE) and primordial mantle-normalized trace element patterns, but have minor negative Nb and Ta anomalies. They are interpreted as mantle plume-related oceanic plateau basalts whose source contained minor continental crustal input. The andesites are characterized by high Mg# (0.66–0.52), Cr and Ni, with depletion of high-field strength elements (HFSE) and enrichment of light REE (LREE) and large-ion lithophile elements (LILE). They were probably derived from a metasomatized mantle wedge overlying a subducted slab in a continental margin subduction zone. The dacites–rhyolites are silicic rocks (SiO 2 =61–72 wt%) with low Cr and Ni, K 2 O/Na 2 O mostly 0.5–1.1, highly fractionated REE patterns, enrichments of LILE and distinctly negative HFSE anomalies. One rhyolite sample yielded a zircon U–Pb age of 2353±32 Ma. This suite is similar to potassic adakites and is explained as the product of deep melting of thickened crust in the arc with a significant older crustal component. Collision between a continental margin arc with an oceanic plateau followed by slab break-off, upwelling of hot asthenosphere and extensive crustal reworking in a sustained compressional regime is proposed for the geodynamic evolution of the area. This is in corroboration with the scenario of EDC as a Neoarchaean hot orogen as suggested recently by some workers. Supplementary material: Details of whole-rock major and trace element determination, Nd isotope analysis and zircon U–Pb dating and trace element analysis, the geographical coordinates of the samples and the values of the international rock standards analysed are available at http://www.geolsoc.org.uk/SUP18660