Evolving early earth: Insights from peninsular India

Abstract

Understanding coupled evolution of the crust-mantle system, building up of habitable continents and tectonics of evolving Earth constitute a major focus of research in Earth and Planetary Sciences. This contribution reviews the processes of the evolution of early Earth, including thermal records, mantle evolution, crustal growth, craton formation and tectonics in the first part, followed by the evolution of individual cratonic blocks in Peninsular India and their assembly into shield framework in the second part. Closely scrutinized global geochronologic and isotope database show that remnants of the Hadean-Eoarchean terrestrial record preserved in the core of cratons provide invaluable insights into planetary evolution. Multidisciplinary studies on the preserved earliest crustal remnants reveal unique features such as distinct lithological associations (tonalite-trondhjemite-granodiorite (TTG)-komatiite dominated greenstones), steeper geothermal gradients, hotter mantle, high rates of crustal growth, dome-basin patterns and plume-dominated tectonics and absence of high-pressure mineral assemblages compared to Phanerozoic Earth. Peninsular India comprises cratons (Dharwar, Bastar, Singhbhum and Bundelkhand) which are surrounded by mobile belts. These cratonic blocks show distinct thermal records, crustal growth patterns, accretionary and tectonic histories. The Dharwar craton is a composite Archean protocontinent that provides a wide time window for accretionary processes of juvenile crust, continental growth and tectonic processes. The craton was built up in successive stages of accretion in plume-arc settings during ca. 3.6, 3.45–3.3, 3.2–3.15, 3.0–2.9, 2.7–2.6 and 2.57–2.52 Ga with three major reworking events linked to cratonization close to 3.1–3.0, 2.64–2.62 and 2.5 Ga. Bastar craton contains TTGs-supracrustal associations and later granite intrusions. The TTG basement accreted episodically during 3.56 and 3.0 Ga, whilst granitoids intruded during ca. 2.5 Ga. The Singhbhum craton preserves several generations of gneisses, granites and greenstone sequences. Geochronologic and Nd-Hf isotope data show prolonged crustal history (ca. 4.2–2.5 Ga) with multistage craton building episodes in the plume-arc settings. The Bundelkhand craton contains TTG-greenstone assemblages intruded by late granitoids. Published ages reveal episodic accretion of TTG-greenstone during ca. 3.54, 3.30 and 2.70 Ga followed by major granitoid emplacement during ca. 2.57–2.52 Ga. The origin of TTG-greenstones is attributed to their derivation from the depleted mantle in arc environments. Petrologic, geochronologic, elemental and isotope data of cratonic blocks revealed their independent crustal histories and assembled into shield framework probably along the Central Indian Tectonic Zone (CITZ). The time frame of amalgamation of cratonic blocks is not clear as documented ages ranging from ca. 1.75 to 1.1–0.95 Ga along major tectonic zones like CITZ and palaeomagnetic poles of mafic dykes from these cratons are much closer during 2.45 Ga. More focused integrated studies are needed to unravel the geological and tectonic history of Peninsular India.