Dharwar Craton

[2][3] The lithologies of the Dharwar Craton are mainly TTG (Tonalite-trondhjemite-granodiorite) gneisses, volcanic-sedimentary greenstone sequences and calc-alkaline granitoids.

[1] The western Dharwar Craton contains the oldest basement rocks, with greenstone sequences between 3.0-3.4 Ga, whereas the central block of the craton mainly contains migmatitic TTG gneisses, and the eastern block contains 2.7 Ga greenstone belts and calc-alkaline plutons.

[4] The formation of the basement rock of the Dharwar Craton was created by intraplate hotspots (i.e., volcanic activities caused by mantle plumes from the core-mantle boundary), the melting of subducted oceanic crust and the melting of thickened oceanic arc crust.

[2] The continuous melting of oceanic arc crust and mantle upwelling generated the TTG and sanukitoid plutons over the Dharwar Craton.

[9] Cratonisation is an important process to form a craton with sufficient and stable continental masses.

[10] In Archean craton, TTG rocks are usually present in batholiths formed by plate subduction and melting.

[2] The volcanic-sedimentary greenstone sequence occupies the majority of the Archean crustal record, which is about 30%.

[2] Sanukitoids are granitoids with high-magnesium composition that are commonly formed by plate collision events in Archean.

[2] According to the zircon U-Pb ages of the TTG gneisses from the Dharwar Craton, there were 5 major accretion events leading to the formation of the Archean felsic continental crust.

[26] The trondhjemite emplacement generated heat and fluid that led to the melting that made the low-density TTG crust rose while the high-density greenstone volcanics sank, which developed the dome-keel structures between the TTG and greenstone.

[28] The weathering and erosion of the microcontinents led to a large amount of detrital input to the ocean floor and subduction zone.

[2] The mafic magma rose and accumulated under the oceanic arc crust, leading to the partial melting of the thickened, incompatible element enriched arc crust and their magma mixed to form the transitional TTGs during 2700–2600 Ma.

[29] The heat from the magma transferred into the surrounding rock leading to the partial melting of gneisses and the formation of calc-alkaline granitoids.

[29] Sanukitoids were formed during the Neoarchean magmatic accretion events, that are originated from the mantle with low silicon dioxide and high magnesium.

[2] The magmatism was followed by the transitional TTG accretion event in 2600 Ma and only occurred in the central and eastern blocks.

The location map of the Dharwar Craton. The shaded area represents the Dharwar Craton. Generated from GeoMapApp (Ryan et al., 2009). [ 1 ]
Simplified geological map of the Dharwar Craton, which shows the western, central and eastern blocks. Modified from Jayananda et al., (2018). [ 2 ]
Simplified cross-section of the Dharwar Craton from SW to NE, showing the shear zone and the granitic intrusions. Modified from Jayananda et al., (2018). [ 2 ]
The graph shows the distribution of zircons according to their U-Pb ages. It shows the 5 major crustal accretion events with the ranges of age 3450–3300, 3230–3200, 3150–3000, 2700–2600 and 2560–2520 Ma. Modified from Jayananda et al, (2015, 2018). [ 2 ] [ 6 ]
The annotated diagram of the intraplate hotspot model before 3400 Ma, forming the oceanic plateaus. Modified from Jayananda et al, (2018). [ 2 ]
The evolutionary diagram of the two-stage melting of the oceanic crust during 3350-3100 Ma, forming the TTG plutons. Modified from Jayananda et al, (2018) and Tushipokla et al, (2013). [ 2 ] [ 5 ]
The model showing the transitional TTG accretion, shifting from the melting of oceanic crust to the melting of the mantle, as well as the sanukitoid magmatism during 2740-2500 Ma. Modified from Jayananda et al, (2013, 2018). [ 2 ] [ 1 ]