Archaean to Palaeoproterozoic crustal evolution of the Aravalli mountain range, NW India, and its hinterland: The U–Pb and Hf isotope record of detrital zircon

Abstract

In situ U–Pb–Hf isotope analyses of detrital zircons from the Alwar quartzite, the oldest member of the North Delhi fold belt in the Aravalli mountain range, indicate that the basement of NW India shares a common Archaean-Palaeoproterozoic evolutionary history, and is a consequence of several crust-forming and crust-reworking events between 3.70 and 1.71 Ga. This is suggested by a zircon age spectrum with most ages at 1.87-1.71 Ga (75%), minor age peaks at 2.5-2.2 and 2.9-2.7 Ga, and Palaeoarchaean ages of 3.27-3.23 Ga. Lu–Hf isotope data reveal that the oldest crust, either in the Aravalli mountain range or in its hinterland, was formed from a depleted mantle source at around 3.7 Ga. Furthermore, the data also indicate that the hinterland of the Alwar sediments was affected by several periods of new “juvenile” crust formation at 3.25, 2.89, 2.67, 2.51, and 1.87-1.80 Ga, while crustal reworking was predominant at 2.62-2.45, 2.2 and 1.87-1.77 Ga. Zircons with xenocrystic cores and metamorphic overgrowths, additionally suggest that the source region was affected by high-grade (?) metamorphic events at 2.5 and 2.2 Ga. Based on our new data, in conjunction with field relationships and existing zircon ages in the Archaean basement of NW India, it can be concluded that the Palaeo- to Neoarchaean detritus (3.3-2.5 Ga) in the Alwar quartzite stems from proximal sources. The predominant late Palaeoproterozoic zircon detritus (1.87-1.71 Ga) was supplied from a nearby basement, which was affected by subduction-accretion tectonics at around 1.85 Ga, and by a first, perhaps post-collisional rift-related phase at 1.77 Ga. The latter event is unrecognized so far, and predates a second phase of rift-related A-type magmatism at 1.72-1.70 Ga. The youngest detrital zircon age of ca. 1.71 Ga suggests that the sedimentation and metamorphism in the North Delhi fold belt postdate the second phase of rift-related A-type magmatic activity.