The Dharwar Craton is an Archean continental crust craton formed between 3.6-2.5 billion years ago (Ga), which is located in southern India and considered as the oldest part of the Indian peninsula.
Studies in the 2010s suggest that the craton can be separated into three crustal blocks since they show different accretionary history (i.e., the history of block collisions). The craton includes the western, central and eastern blocks and the three blocks are divided by several shear zones.
The lithologies of the Dharwar Craton are mainly TTG (Tonalite-trondhjemite-granodiorite) gneisses, volcanic-sedimentary greenstone sequences and calc-alkaline granitoids. 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.
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. The continuous melting of oceanic arc crust and mantle upwelling generated the TTG and sanukitoid plutons over the Dharwar Craton.
Overview of the regional geology
Traditionally, the Dharwar Craton includes the western block and eastern block. The mylonite zone at the eastern boundary of the Chitradurga greenstone belt is the margin between the western block and the eastern block. The Chitradurga greenstone belt is an elongated linear supracrustal belt which is 400 km long from North to South.
Cratonisation is an important process to form a craton with sufficient and stable continental masses. In terms of the ages of the blocks, the western blocks is older with a cratonisation age around 3.0 Ga while the eastern block is younger with the cratonisation age around 2.5 Ga.
|Simplified stratigraphic column of the Dharwar Craton|
|Sargur group (3.3-3.0 Ga)|
|Dharwar supergroup (2.9-2.6 Ga)|
|Kolar group (2.7 Ga)|
|Granitic plutons (2.7-2.5 Ga)|
TTG rocks are intrusive rocks with a granitic composition of quartz and feldspar but contain less potassium feldspar. In Archean craton, TTG rocks are usually present in batholiths formed by plate subduction and melting. Two kinds of gneisses can be found on the Dharwar Craton, which includes the typical TTG-type gneisses (i.e., traditional TTG with a major component of quartz and plagioclase) and the dark grey TTG banded gneisses (relatively more potassium feldspar than typical TTG gneisses):
|Blocks||Associated group||Main TTG type||Characteristics|
|western block||Sargur Group||typical TTG gneisses||
|central block||Kolar Group||transitional TTG gneisses (contain both typical TTG and dark grey banded gneisses)|
|eastern block||Kolar Group||banded gneisses||
Volcanic-sedimentary greenstone sequences
Greenstone is metamorphosed mafic to ultramafic volcanic rock that formed in volcanic eruptions in the early stage of Earth formation. The volcanic-sedimentary greenstone sequence occupies the majority of the Archean crustal record, which is about 30%. The western block comprises the greenstone sequences with adequate sediments, while the central block and the eastern block comprise the greenstone sequences with adequate volcanic rocks but minor sediments.
|Blocks||Associated group(s)||Composition of the volcanic greenstone||Characteristics|
|Western block||Sargur group and Dharwar Supragroup||ultramafic komatiite with interlayered sediments|
|Central block||Kolar group||basalts with minor ultramafic komatiite||
|Eastern block||Kolar group||basalts with minor ultramafic komatiite|
Sanukitoids (Calc-alkaline granitoids)
Sanukitoids are granitoids with high-magnesium composition that are commonly formed by plate collision events in Archean. In the Dharwar Craton, there is no sanukitoid record in the western block. However, there are a lot of granitoid intrusions in the central block, which become less in the eastern block.
|Blocks||Rock units intruded by granitoids||Main composition||Characteristics|
|Central block||TTG gneisses and volcanic greenstone||monzogranite and monzodiorite|
Anatectic granite is a kind of rock formed by the partial melting of the pre-existing crustal rock, which is relatively younger than the TTG and greenstone in the Dharwar Craton. The granites usually cut across the older rocks.
|Blocks||Rock units intruded by granites||Main composition||Characteristics|
|Western block||TTG gneisses and volcanic greenstone||granite with high-potassium content||
When the rocks were under subductions, they experienced high temperature and pressure leading to the chemical changes and textural changes of rocks (i.e., metamorphism). The mineral assemblages of the metamorphic rocks can tell us how high the temperature and pressure are when they are under the peak metamorphism (the progress with the highest pressure and temperature). The metamorphic rocks in the Dharwar Craton usually recorded the mineral assemblages from amphibolite facies to granulite facies:
|Blocks||Pressure-Temperature conditions||Metamorphic facies||Records|
|Western block||Progressive increase from the N to the S||From the greenschist facies to the hornblende-granulite facies ||Holenarsipur greenstone belt
|Central block||Progressive increase from the N to the S||From the greenschist facies to the granulite facies||Pavagada region, the central part of the central block
B.R Hills region
|Eastern block||Poorly understood||Poorly understood||Hutti greenstone belt
Archean crust accretions
Accretions mean the collisions between plates leading to the plate subduction. Crust accretions are important in the Dharwar Craton since the continuous volcanic eruptions caused by accretions led to the formation of Archean felsic continent crust.
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. The events occurred with the ranges of age 3450–3300, 3230–3200, 3150–3000, 2700–2600 and 2560–2520 million years ago (Ma).
The western block records the two earliest crust accretion events, that happened in 3450 Ma and 3230 Ma. The rates of the continental growth of the two events are fast since the events led to the widespread of greenstone volcanism.
The central block records 4 major accretion events, that occurred in 3375 Ma, 3150 Ma, 2700 Ma and 2560 Ma. The isotopic data suggests that the scale of the continental growth due to felsic crust accretion was large during 2700–2600 Ma and 2560–2520 Ma, leading to the large-scale greenstone volcanism at that time. 
The eastern block records the 2 latest major accretion events occurring in 2700 Ma and 2560 Ma with massive continental growth.
Crustal reworking events
Crustal reworking means the old rocks (protoliths) are destroyed and regenerated into new rocks. The continental crust is relatively old if the crust experienced crustal reworking events. For the rocks that experienced crustal reworking, minerals like zircon, which is difficult to melt, are preserved in the reworked rocks. Some new zircons with a younger age would be formed in the reworking events.
The crustal reworking events happened in the time range of 3100–3000 Ma. All 3 crustal blocks record the crustal reworking events in 2520 Ma due to the final assembly of the Superia supercontinent. 
For the western block, there are two reworking events. The first event happened in 3100–3000 Ma accounting to the emplacement of granite. The second reworking event led to the emplacement of 2640–2600 Ma of granites.
For the central block, the event happened in 3140 Ma is considered as the earliest crustal reworking due to the TTG accretion event between 3230–3140 Ma in the central block of the craton.
For the eastern block, the second highest-temperature reworking event was recorded in the centre of the block, which happened in 2640–2620 Ma. The reworking event is related to the greenstone volcanism of the TTG accretion event in 2700 Ma.
Formation and evolution
Intraplate hotspot model
Before 3400 Ma, the magma upwelling from the mantle led to the intraplate hotspot setting. The upwelling magma formed the oceanic plateaus with komatiites and komatiitic basalts in the oceanic crust.
Two-stage melting of oceanic crust
After the mantle plume hotspots were formed, the tectonic setting was followed by the two-stage melting, which include the melting of the subducted oceanic crust and the melting of the thickened oceanic arc crust.
In 3350 Ma, due to the ridge push from the oceanic spreading centres (mid-oceanic ridges), some oceanic crust subducted under the mantle. The subduction led to the melting of the subducted crust and formed magma that rose to the oceanic crust and formed oceanic island arc crust.
During 3350–3270 Ma, the mafic to ultramafic hydrous melt formed by the slab melting melted the base of the thickened oceanic arc crust, which formed the TTG melt, as well as magmatic protoliths of TTGs in the oceanic arc crust.
During 3230–3100 Ma, the continuous collision of the oceanic island arc crust, the TTG and oceanic plateaus, that are formed in the previous stage, caused the melting of the juvenile crust in the oceanic island arc, which generated trondhjemite plutons in 3200 Ma. 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.
Stage of transitional TTGs
The transitional TTGs, which were recorded in the central and eastern blocks, was formed during 2700–2600 Ma. The transitional TTGs are relatively enriched in incompatible elements. The enrichment of the incompatible elements could be account for the high-angle subduction and the chemical interaction between the mantle wedge and the melt from the subducted crust.
During the 2700 Ma, the central and eastern block of the Dharwar Craton had developed into microcontinents. The weathering and erosion of the microcontinents led to a large amount of detrital input to the ocean floor and subduction zone. Therefore, the subducted slab with a large amount of sediment brought incompatible elements into the mantle due to a high-angle subduction. The mantle wedge interacted with the slab, leading to the partial enrichment of the incompatible elements in the wedge and generated mafic to intermediate magma. 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.
Shifting from oceanic crust melting to mantle melting
After the transitional TTG accretion, the inflexible subducted oceanic crust broke and fell into the asthenosphere, leading to the mantle upwelling under the pre-existing crust. The upwelling mantle rock rose to the shallow depth and melted the upper mantle to generate intermediate to mafic magma. Then, the magma intruded into the middle part of the crust. It underwent differentiation in magma chambers. The heat from the magma transferred into the surrounding rock leading to the partial melting of gneisses and the formation of calc-alkaline granitoids.
Sanukitoids were formed during the Neoarchean magmatic accretion events, that are originated from the mantle with low silicon dioxide and high magnesium. The sanukitoid magma could be generated by either plate subduction or plume setting.
The sanukitoids created by subduction might lead to the chemical alteration of the mantle wedge and the melting of the wedge. The peridotitic mantle wedge was mixed with intermediate to felsic melts. This can be explained by the mixing of the previous TTG melts. The sanukitoids created by plume setting would lead to the sanukitoid intrusions with high magnesium content and low silicon dioxide.
The sanukitoid magmatism is not related to the TTG accretion events during 3450–3000 Ma. The magmatism was followed by the transitional TTG accretion event in 2600 Ma and only occurred in the central and eastern blocks. Since the sanukitoids are enriched in both incompatible and compatible elements, while the TTGs are not, it indicates the appearance of the sanukitoid magmatism shows the tectonic change from melting of oceanic crust to melting of mantle during the period of 2600–2500 Ma.
Closure of subduction zones
During 2560–2500 Ma, the three blocks joined together to form the Dharwar Craton and all the subduction zones closed, followed by the regional metamorphism due to heat release from the mantle during 2535–2500 Ma. The final cratonisation finished in 2400 Ma through slow cooling.
Implication for global crust history
|Cratons||Characteristics||Possible relationships with the Dharwar Craton|
|North China Craton||
- Jayananda, M.; Peucat, J.-J.; Chardon, D.; Rao, B. Krishna; Fanning, C.M.; Corfu, F. (April 2013). "Neoarchean greenstone volcanism and continental growth, Dharwar craton, southern India: Constraints from SIMS U–Pb zircon geochronology and Nd isotopes". Precambrian Research. 227: 55–76. Bibcode:2013PreR..227...55J. doi:10.1016/j.precamres.2012.05.002. hdl:1885/71644.
- M., Jayananda; M., Santosh; K.R., Aadhiseshan (June 2018). "Formation of Archean (3600–2500 Ma) continental crust in the Dharwar Craton, southern India". Earth-Science Reviews. 181: 12–42. Bibcode:2018ESRv..181...12J. doi:10.1016/j.earscirev.2018.03.013. S2CID 243889151.
- Peucat, Jean-Jacques; Jayananda, Mudlappa; Chardon, Dominique; Capdevila, Ramon; Fanning, C. Mark; Paquette, Jean-Louis (April 2013). "The lower crust of the Dharwar Craton, Southern India: Patchwork of Archean granulitic domains". Precambrian Research. 227: 4–28. Bibcode:2013PreR..227....4P. doi:10.1016/j.precamres.2012.06.009.
- Lancaster, Penelope J.; Dey, Sukanta; Storey, Craig D.; Mitra, Anirban; Bhunia, Rakesh K. (December 2015). "Contrasting crustal evolution processes in the Dharwar craton: Insights from detrital zircon U–Pb and Hf isotopes". Gondwana Research. 28 (4): 1361–1372. Bibcode:2015GondR..28.1361L. doi:10.1016/j.gr.2014.10.010.
- Tushipokla; Jayananda, M. (2013). "Geochemical constraints on komatiite volcanism from Sargur Group Nagamangala greenstone belt, western Dharwar craton, southern India: Implications for Mesoarchean mantle evolution and continental growth". Geoscience Frontiers. 4 (3): 321–340. doi:10.1016/j.gsf.2012.11.003.
- Jayananda, M.; Chardon, D.; Peucat, J.-J.; Fanning, C.M. (October 2015). "Paleo- to Mesoarchean TTG accretion and continental growth in the western Dharwar craton, Southern India: Constraints from SHRIMP U–Pb zircon geochronology, whole-rock geochemistry and Nd–Sr isotopes". Precambrian Research. 268: 295–322. Bibcode:2015PreR..268..295J. doi:10.1016/j.precamres.2015.07.015. hdl:1885/98524.
- Gao, Pin; Santosh, M. (September 2020). "Mesoarchean accretionary mélange and tectonic erosion in the Archean Dharwar Craton, southern India: Plate tectonics in the early Earth". Gondwana Research. 85: 291–305. Bibcode:2020GondR..85..291G. doi:10.1016/j.gr.2020.05.004. S2CID 219911858.
- Ramakrishnan, M.; Nath, J. Swami (1981). Early Precambrian Supracrustals of Southern Karnataka. Geological Survey of India. p. 350.
- Hokada, T.; Horie, K.; Satish-Kumar, M.; Ueno, Y.; Nasheeth, A.; Mishima, K.; Shiraishi, K. (2013). "An appraisal of Archaean supracrustal sequences in Chitradurga Schist Belt, Western Dharwar Craton, Southern India". Precambrian Research. 227: 99–119. Bibcode:2013PreR..227...99H. doi:10.1016/j.precamres.2012.04.006.
- Chardon, D.; Jayananda, M.; Peucat, J.-J. (2011). "Lateral constrictional flow of hot orogenic crust: Insights from the Neoarchean of south India, geological and geophysical implications for orogenic plateaux" (PDF). Geochemistry, Geophysics, Geosystems. 12 (2). Bibcode:2011GGG....12.2005C. doi:10.1029/2010GC003398. S2CID 53523396.
- Maya, J.M.; Bhutani, R.; Balakrishnan, S.; Rajee Sandhya, S. (2017). "Petrogenesis of 3.15 Ga old Banasandra komatiites from the Dharwar craton, India: Implications for early mantle heterogeneity". Geoscience Frontiers. 8 (3): 467–481. doi:10.1016/j.gsf.2016.03.007.
- Kumar, A.; Rao, Y.J.B.; Sivaraman, T.V.; Gopalan, K. (1996). "Sm–Nd ages of Archaean metavolcanics of the Dharwar craton, South India". Precambrian Research. 80 (3–4): 205–216. doi:10.1016/S0301-9268(96)00015-0.
- Balakrishnan, S.; Rajamani, V.; Hanson, G.N. (1999). "U‐Pb Ages for Zircon and Titanite from the Ramagiri Area, Southern India: Evidence for Accretionary Origin of the Eastern Dharwar Craton during the Late Archean". The Journal of Geology. 107 (1): 69–86. Bibcode:1999JG....107...69B. doi:10.1086/314331. S2CID 129230869.
- Manikyamba, C.; Kerrich, R. (2012). "Eastern Dharwar Craton, India: Continental lithosphere growth by accretion of diverse plume and arc terranes". Geoscience Frontiers. 3 (3): 225–240. doi:10.1016/j.gsf.2011.11.009.
- Jayananda, M.; Gireesh, R.V.; Sekhamo, K.; Miyazaki, T. (2014). "Coeval felsic and Mafic Magmas in neoarchean calc-alkaline magmatic arcs, Dharwar craton, Southern India: Field and petrographic evidence from mafic to Hybrid magmatic enclaves and synplutonic Mafic dykes". Journal of the Geological Society of India. 84 (1): 5–28. doi:10.1007/s12594-014-0106-2. S2CID 129774961.
- Harish Kumar, S.B., Jayananda, M., Kano, T., Shadakshara Swamy, N., Mahabaleshwar, B., 2003. Late Archean juvenile accretion process in the Eastern Dharwar Craton; Kuppam–Karimangala area. Mem. Geol. Soc. India 50, 375–408.
- Bouhallier, H., 1995. Evolution structurale et métamorphique de la croûte continentale archéenne (craton de Dharwar, Inde du sud). Mém. Doc.. 60 Géosciences-Rennes (277p).
- Pichamuthu, C.S., 1965. Regional metamorphism and charnockitisation in Mysore state, India. Indian Mineralogist 6, 116–126.
- Jayananda, M.; Banerjee, M.; Pant, N.C.; Dasgupta, S.; Kano, T.; Mahesha, N.; Mahabaleswar, B. (2012). "2.62 Ga high-temperature metamorphism in the central part of the Eastern Dharwar Craton: implications for late Archaean tectonothermal history". Geological Journal. 47 (2–3): 213–236. doi:10.1002/gj.1308. S2CID 128668525.
- Prabhakar, B.C.; Jayananda, M.; Shareef, M.; Kano, T. (2009). "Synplutonic mafic injections into crystallizing granite pluton from Gurgunta area, northern part of Eastern Dharwar Craton: Implications for magma chamber processes". Journal of the Geological Society of India. 74 (2): 171–188. doi:10.1007/s12594-009-0120-y. S2CID 140621595.
- Hansen, E.C.; Newton, R.C.; Janardhar, A.S.; Lindenberg, S. (1995). "Differentiation of Late Archean Crust in the Eastern Dharwar Craton, Krishnagiri-Salem Area, South India". The Journal of Geology. 103 (6): 629–651. Bibcode:1995JG....103..629H. doi:10.1086/629785. S2CID 140729072.
- Balakrishnan, S.; Hanson, G.N.; Rajamani, V. (1991). "Pb and Nd isotope constraints on the origin of high Mg and tholeiitic amphibolites, Kolar Schist Belt, South India". Contributions to Mineralogy and Petrology. 107 (3): 279–292. Bibcode:1991CoMP..107..279B. doi:10.1007/BF00325099. S2CID 128546587.
- Jayananda, M.; Chardon, D.; Peucat, J.-J.; Capdevila, R. (2006). "2.61 Ga potassic granites and crustal reworking in the western Dharwar craton, southern India: Tectonic, geochronologic and geochemical constraints". Precambrian Research. 150 (1–2): 1–26. Bibcode:2006PreR..150....1J. doi:10.1016/j.precamres.2006.05.004.
- Jayananda, M.; Kano, T.; Peucat, J.; Channabasappa, S. (2008). "3.35 Ga komatiite volcanism in the western Dharwar craton, southern India: Constraints from Nd isotopes and whole-rock geochemistry". Precambrian Research. 162 (1–2): 160–179. Bibcode:2008PreR..162..160J. doi:10.1016/j.precamres.2007.07.010.
- Adam, J.; Rushmer, T.; O'Neil, J.; Francis, D. (2012). "Hadean greenstones from the Nuvvuagittuq fold belt and the origin of the Earth's early continental crust". Geology. 40 (4): 363–366. Bibcode:2012Geo....40..363A. doi:10.1130/G32623.1.
- Bouhallier, H.; Choukroune, P.; Ballèvre, M. (1993). "Diapirism, bulk homogeneous shortening and transcurrent shearing in the Archaean Dharwar craton: the Holenarsipur area, southern India". Precambrian Research. 63 (1–2): 43–58. Bibcode:1993PreR...63...43B. doi:10.1016/0301-9268(93)90004-L.
- Martin, H.; Moyen, J.-F. (2002). "Secular changes in tonalite-trondhjemite-granodiorite composition as markers of the progressive cooling of Earth". Geology. 30 (4): 319–322. Bibcode:2002Geo....30..319M. doi:10.1130/0091-7613(2002)030<0319:SCITTG>2.0.CO;2.
- Foley, S.; Tiepolo, M.; Vannucci, R. (2002). "Growth of early continental crust controlled by melting of amphibolite in subduction zones". Nature. 417 (6891): 837–840. Bibcode:2002Natur.417..837F. doi:10.1038/nature00799. PMID 12075348. S2CID 4394308.
- Friend, C.R.L., 1984. The origins of the closepet granites and implications of crustal evolution in southern Karnataka. J. Geol. Soc. India 25, 73–84.
- Jayananda, M.; Moyen, J.-F.; Martin, H.; Peucat, J.-J.; Auvray, B.; Mahabaleswar, B. (2000). "Late Archaean (2550–2520 Ma) juvenile magmatism in the Eastern Dharwar craton, southern India: constraints from geochronology, Nd–Sr isotopes and whole rock geochemistry". Precambrian Research. 99 (3–4): 225–254. Bibcode:2000PreR...99..225J. doi:10.1016/S0301-9268(99)00063-7.
- Kelemen, P.B. (1995). "Genesis of high Mg# andesites and the continental crust". Contributions to Mineralogy and Petrology. 120 (1): 1–19. Bibcode:1995CoMP..120....1K. doi:10.1007/BF00311004. S2CID 129100194.
- Smithies, R.H.; Champion, D.C. (2000). "The Archaean High-Mg Diorite Suite: Links to Tonalite-Trondhjemite-Granodiorite Magmatism and Implications for Early Archaean Crustal Growth". Journal of Petrology. 41 (12): 1653–1671. doi:10.1093/petrology/41.12.1653.
- Peucat, J.-J.; Jayananda, M.; Chardon, D.; Capdevila, R.; Fanning, C.M.; Paquette, J.-L. (2013). "The lower crust of the Dharwar Craton, Southern India: Patchwork of Archean granulitic domains". Precambrian Research. 227: 4–28. Bibcode:2013PreR..227....4P. doi:10.1016/j.precamres.2012.06.009.
- Kaur, P.; Zeh, A.; Chaudhri, N. (2014). "Characterisation and U–Pb–Hf isotope record of the 3.55Ga felsic crust from the Bundelkhand Craton, northern India". Precambrian Research. 255: 236–244. Bibcode:2014PreR..255..236K. doi:10.1016/j.precamres.2014.09.019.
- Zhai, M.G.; Santosh, M. (2011). "The early Precambrian odyssey of the North China Craton: A synoptic overview". Gondwana Research. 20 (1): 6–25. Bibcode:2011GondR..20....6Z. doi:10.1016/j.gr.2011.02.005.
- Laurent, O.; Martin, H.; Doucelance, R.; Moyen, J.-F.; Paquette, J.-L. (2011). "Geochemistry and petrogenesis of high-K 'sanukitoids' from the Bulai pluton, Central Limpopo Belt, South Africa: Implications for geodynamic changes at the Archaean–Proterozoic boundary". Lithos. 123 (1–4): 73–91. Bibcode:2011Litho.123...73L. doi:10.1016/j.lithos.2010.12.009.
- Cassidy, K.F., Champion, D.C., Krapez, B., Barley, M.E., Brown, S.J.A., Blewett, R.S., Groenewald, P.B., Tyler, I.M., 2006. A Revised Geological Framework for the Yilgarn Craton: Geological Survey of Western Australia. (Record 2006/8, 8p).
- Kabete, J.M.; McNaughton, N.J.; Groves, D.I.; Mruma, A.H. (2012). "Reconnaissance SHRIMP U–Pb zircon geochronology of the Tanzania Craton: Evidence for Neoarchean granitoid–greenstone belts in the Central Tanzania Region and the Southern East African Orogen". Precambrian Research. 216–219: 232–266. Bibcode:2012PreR..216..232K. doi:10.1016/j.precamres.2012.06.020.
- Schofield, D.I.; Thomas, R.J.; Goodenough, K.M.; De Waele, B.; Pitfield, P.E.J.; Key, R.M.; Bauer, W.; Walsh, G.J.; Lidke, D.J.; Ralison, A.V. (2010). "Geological evolution of the Antongil Craton, NE Madagascar". Precambrian Research. 182 (3): 187–203. Bibcode:2010PreR..182..187S. doi:10.1016/j.precamres.2010.07.006.