U–Pb and Hf isotope study of detrital zircon and Cr-spinel in the Banavara quartzite and implications for the evolution of the Dharwar Craton, south India

Abstract

The Sargur Group has been considered to be the oldest group (>3.0 Ga) in the Archaean sequence of the Dharwar Craton in south India, whereas the rocks of the Dharwar Supergroup are younger (between 3.0 and 2.55 Ga). The supracrustal units of the Sargur Group were deposited during the Archaean period. The Banavara quartzite forms part of the supracrustal Sargur Group and contains significant amounts of chromian spinel (Cr-spinel). Here, U–Pb and Hf isotopes of detrital zircons are integrated with compositional data and X-ray refinement parameters for Cr-spinels to decipher the provenance of the metasediments. Zircons show an age spectrum from 3.15 to 2.50 Ga, and juvenile Hf isotopic compositions (ϵHf = +0.8 to +6.4) with model ages between 3.3 and 3.0 Ga. Major- and trace-element contents of the Cr-spinels do not resemble those in the Sargur ultramafic rocks, but resemble well-characterized Archaean anorthosite-hosted chromites. Cr-spinel trace-element signatures indicate that they have undergone secondary alteration or metamorphism. X-ray refinement parameters for the Cr-spinels also resemble the anorthosite-hosted chromites. We conclude that the detrital minerals were probably derived from gneissic and anorthositic rocks of the Western Dharwar Craton, and that the Sargur Group sequences have experienced a younger (2.5 Ga) metamorphic overprint.

The Effects of High-Grade Metamorphism on Cr-Spinel from the Archean Sittampundi Complex, South India

“…In Figure 4, we compare the structural parameters of the studied Cr-spinels with those of other occurrences that are similar in age. In fact, there are some other Archean occurrences, such as the Fiskenaesset and Ujragassuit (Greenland) [35], Amsaga (Mauritania) [34], Inyala and Rhonda (Limpopo belt, Zimbabwe) [35], detrital Cr-spinels from Banavara [66], as well as the Bushveld and Stillwater Complexes [31,33]. Moreover, the figure comprises the Cr-spinels in seams entrapped within anorthosites from the Paleogene Rum Layered Complex [32].…”

“…Figure 4.Oxygen positional parameter, u, versus cell edge, a. Black circles: Cr-spinels from Sittampundi (this study); red circles: detrital Cr-spinels from Banavara[66]; grey circles, squares and star: Cr-spinels from Amsaga (Mauritania) in amphibole, chlorite and talc-serpentine matrix, respectively[34]; yellow, purple and green circles: Cr-spinels from Fiskenaesset and Ujragassuit (Greenland) and Zimbabwe, respectively[35]; blue squares: Cr-spinels from Rum (Scotland)[32]; green field: Cr-spinels from Bushveld and Stillwater complexes[31,33]; yellow field: Cr-spinels from Nuggihalli komatiites[69].…”

The Österplana Fossil Meteorites and… What Else? Terrestrial Cr-Spinels and Zircons in the Ordovician Limestones of the Thorsberg Quarry (Sweden)

“…The composition of the detrital Cr-spinels found in Kinnekulle resembles that of the ferrianchromite rims of Cr-spinels from those ophiolites, but the detritals are usually richer in TiO 2 . This fact, the low Mg#, i.e., Mg/(Fe 2+ + Mg) and the enrichment of MnO could suggest a possible secondary process [38].…”