The Dharwar Craton
The Dharwar Craton
The Dharwar Craton in southern India is one of oldest classic Archean terrains and holds clues about our planet's early history, spanning over 3.0 billion years. This study reveals that ultramafic and mafic rocks from the Holenarsipur Nucleus originated from deep within the Earth's mantle. The geochemical and isotopic results suggest that these rocks were formed in two different tectonic settings, indicating a shift from vertical to horizontal tectonic environments during the Paleo- to Mesoarchean. Also, the study documented vestiges of a depleted mantle reservoir beneath the cratonic core of the Western Dharwar Craton dating back to the Paleo- to Mesoarchean.
Schematic diagram illustrating the evolution and transition from vertical to horizontal tectonics during the formation of the Holenarsipur Nucleus, Dharwar Craton
The Dharwar Craton (DC) in southern India is one of the classic Archean terrains, preserving an evolutionary history from the Paleoarchean to Mesoarchean. The present study attempts to understand the origin and evolution of mafic (amphibolites) and ultramafic (harzburgite) rocks from the Holenarsipur Greenstone Belt (HGB), to decipher the evolution of the cratonic core of the Western Dharwar Craton (WDC). Relict olivine and orthopyroxene pseudomorphs and neodymium isotopic compositions reveal that harzburgites from the HGB represent a preserved section of the early Archean mantle, re-fertilized by fluid/rock interaction during serpentinization.
The ultramafic and mafic rocks from the southern and northern parts of the belt exhibit coherent whole-rock geochemical and Nd isotopic compositions. Ultramafic rocks were derived from a depleted mantle source (ƐNd(t=3300)= +0.65 to +8.70) while, the amphibolites were generated by partial melting of an enriched mantle source (ƐNd(t=3300) = -4.16 to +0.92).
The ultramafic rocks with fore-arc affinity may signify the prevalence of a subduction setting during the early stages of the first accretionary event in the WDC. The compositionally uniform mafic rocks from the HGB with oceanic plateau affinity affirm a plume environment. Our study establishes the prevalence and transition from vertical to horizontal tectonics during the Paleo- to Mesoarchean evolution of the WDC.
Also, the study identified vestiges of a depleted mantle reservoir beneath the cratonic core of the Western Dharwar Craton (WDC) dating back to the Paleo- to Mesoarchean.
