Evolving Archean Earth: Insights from the Dharwar craton, Southern India

The Dharwar craton form a wide time (3.6-2.5 Ga) window for the Archean Earth forming an ideal target to address processes involved in building of habitable continents. This craton preserves a large titled crustal panel comprising granitoids (TTGs), volcanic-sedimentary greenstone assemblages and potassic granites. The craton divided into Western and Eastern blocks based on age of the basement, structures, thermal records and crustal thickness. Tectonic fabrics analysis combined with U-Pb zircon data reveal 3.6-3.23 Ga basement and 3.1 Ga dome-keel patterns in the Western block whilst abundant 2.7-2.56 Ga juvenile crust with remnants of 3.3-3.1 Ga crust traversed by closely spaced interfering 2.5 Ga shear zones in the Eastern block. Isotopic age data together with elemental and whole rock Nd coupled with in-situ zircon Hf isotope data reveal craton evolution in three major stages: (i) 3.6-3.3 Ga TTG-komatiite assemblages in the cratonal core in the Western block forming micro-continent, oceanic plateaus or island arcs or oceanic crust. These tectonic units assembled through subduction of intervening oceanic crust by 3.3 Ga and eventual slab break-off cause mantle upwelling generate hot trondhjemite magmas which drive partial convective overturn producing dome-keel patterns by 3.2 Ga. (ii) Rise of continental crust above sea level ca. 3.0 Ga evidenced by paleosol with development of intracratonic basins (Bababudan-Kudremukh basins). Strain fabrics mapping and kinematic analysis reveal radial centripetal collapse of high-density greenstone load into low density granitoid basement. (iii) Combined tectonic fabrics analysis, petrologic and elemental data reveal that 2.74-2.67 Ga greenstone basins developed in arc settings. Collision of those arcs and eventual slab breakoff drives mantle upwelling causing a major outburst of 2.6-2.5 Ga juvenile accretion forming a hot orogen. Lateral flow of hot orogenic crust with eventual assembly with western block by 2.5 Ga led to final cratonization. The craton built through transient tectonics from vertical accretion to horizontal motion during 3.6-2.5 Ga. Redox sensitive elements and isotope biomarkers (Fe, N) of 2.72 Ga BIFs reveal fluctuation in oxygen generation at ocean surface attributed to biologically mediated processes of Fe recycling and photosynthesis.