Evolution of the Archean felsic crust of Singhbhum Craton, India: A reassessment

The Precambrian Singhbhum Craton and the adjoining orogenic belts of eastern India hold a history of continental crust generation by repeated emplacement and reworking of multiphase tonalite-trondjhemite-granodiorite (TTG) and granites throughout the Archean. Temporal classification of this complex Archean TTG and granite sequence have not been straightforward due to repeated magmatism that gave rise to complex intrusive relationships between the magmatic bodies, their complex tectonic juxtaposition and lack of geochronological data. Recent surge of new geochronological and isotope data has brought significantl clarity in the temporal relationships between different crustal components of this craton. In this study, geochemical data (published and new) of the TTG and granites (n = 251) with robust age reference was compiled and classified using a two-fold (viz. age and geochemistry) classification to understand the secular change of crustal composition. Herein, the Archean TTG suites were divided into four age-based groups, viz. Group-I (> ca. 3.5-3.4 Ga), II (ca. 3.4-3.3 Ga), III (ca. 3.3-3.2 Ga) and IV (< ca. 3.2 Ga). This reveals relative abundance of TTG and granite components vary systematically from one temporal group to another. Time defined locally weighted, non-linear regression trends show that the composition of Singhbhum continental crust experienced a transition at ca. 3.4 Ga, before which low-Mg#, sodic TTG prevailed. After ca. 3.4 Ga, the crust was gradually replaced by more potassic, transitional TTG and granites. TTG to granite transition in this craton took place at ca. 3.3 Ga after which proportion of granites spiked significantly. Finally from ca. 3.2 Ga, more evolved, potassic granites started emerging throughout the craton. Prevalence of low-Mg# TTGs indicates that subduction may not have played a significant role in generating the TTGs. Dominance of potassic granitoids confirm that crustal reworking became a dominant process as early as the Paleoarchean. Prevalence of peraluminous granites after ca. 3.4 Ga indicates that the Singhbhum cratonic crust matured very early in the Earth's history.

Automated summary

The Precambrian Singhbhum Craton and the adjoining orogenic belts in eastern India have a complex history of continental crust generation through repeated magmatic activity. Recent geochronological and isotope data have provided insights into the temporal relationships between different crustal components in this region.