Detrital zircon U-Pb ages and Hf-isotope systematics from the Gadag Greenstone Belt: Archean crustal growth in the western Dharwar Craton, India

摘要

The Western Dharwar Craton in peninsular India comprises a typical Meso- to Neo-Archean granite-greenstone terrain. Detrital zircons from two metagreywackes in a late basin from the Gadag Greenstone Belt preserve at least eight age populations ranging in age from ca 3.34 to 2.55Ga, and grains as old as ca 3.54Ga. The zircon provenances for the two samples appear to be the same up to ca 3.25Ga, with relatively juvenile ε _(Hf) values largely between zero and depleted mantle values. After 3.25Ga, one sample has similar ε _(Hf) values whereas the other has only negative values indicative of Hf-evolution in a crustal environment. After ca 3.25Ga the source regions for the two samples were distinctly different.The detrital zircons reflect the age and evolution of the upper crust of the Western Dharwar Craton. Modeling of Hf isotopic evolution of the detrital zircons suggests two major crust-forming events at ca. 3.6 and 3.36. Ga, and some indication of juvenile addition to the crust at ca 2.6. Ga. The maximum sedimentation age of the greywackes is constrained by the youngest detrital zircon population at 2547 ± 5. Ma. Gold mineralization in the belt is dated at 2522 ± 6. Ma and constrains greywacke sedimentation, deformation and metamorphism to a ca 25. my interval.