Contrasting geochronological evolution of the Rajpura-Dariba and Rampura-Agucha metamorphosed Zn-Pb deposit, Aravalli-Delhi Belt, India
The timing of metamorphism of the Rajpura-Dariba and Rampura-Agucha massive sulfide deposits in the Aravalli-Delhi Belt, India has been constrained through U-Th-Pb chemical dating of monazite from the host rocks of these deposits. The Rampura-Agucha deposit was metamorphosed during the Neoproterozoic (ca. 1.0 Ga) Grenville-age collisional orogeny. Metamorphic domains in monazite from the host rocks of the Rajpura-Dariba deposit furnish Mesoproterozoic (1621 ± 42 Ma) ages with no evidence of any Neoproterozoic metamorphism. A Paleoproterozoic (1869 ± 22 Ma) age cluster from the Dariba monazites corroborates the ca. 1800 Ma published Pb-isotope model age of sulfide mineralization. As the lithotectonic association and Pb-isotope model age of the Agucha deposit is similar to that of the Dariba deposit, the former should also have been affected by the Mesoproterozoic event. Monazites from Agucha preserve little evidence of the Mesoproterozoic metamorphism possibly because the Neoproterozoic high-grade metamorphic event affecting the rocks almost completely re-equilibrated pre-existing grains. Thus, the Rajpura-Dariba deposit has experienced a single tectonothermal event (at ca. 1.62 Ga) while the Rampura-Agucha deposit has undergone two metamorphic events at ca. 1.62 Ga and 1.0 Ga. This difference is because the Rampura-Agucha deposit is located close to or within the Grenvillian orogenic front in the Aravalli-Delhi Belt whereas the Rajpura-Dariba deposit is far away from the Grenvillian orogenic front and hence was unaffected by it.