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Geological Magazine; March 2007; v. 144; no. 2; p. 361-378; DOI: 10.1017/S0016756806002950
© 2007 Cambridge University Press (CUP)
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Geochemistry, zircon ages and whole-rock Nd isotopic systematics for Palaeoproterozoic A-type granitoids in the northern part of the Delhi belt, Rajasthan, NW India: implications for late Palaeoproterozoic crustal evolution of the Aravalli craton

PARAMPREET KAUR*,{dagger},{ddagger}, NAVEEN CHAUDHRI{dagger}, INGRID RACZEK*, ALFRED KRÖNER§ and ALBRECHT W. HOFMANN*

* Max-Planck-Institut für Chemie, Postfach 3060, 55020 Mainz, Germany
{dagger} Centre of Advanced Study in Geology, Panjab University, Chandigarh, 160 014, India
§ Institut für Geowissenschaften, Universität Mainz, 55099 Mainz, Germany

{ddagger} Author for correspondence: param.geol{at}gmail.com

Determination of zircon ages as well as geochemical and Sm–Nd isotope systematics of granitoids in the Khetri Copper Belt of the Aravalli mountains, NW India, constrain the late Palaeoproterozoic crustal evolution of the Aravalli craton. The plutons are typical A-type within-plate granites, derived from melts generated in an extensional tectonic environment. They display REE and multi-element patterns characterized by steep LREE-enriched and almost flat HREE profiles and distinct negative anomalies for Sr, P and Ti. Initial {varepsilon}Nd values range from – 1.3 to – 6.2 and correspond to crustal sources with mean crustal residence ages of 2.5 to 2.1 Ga. A lower mafic crustal anatectic origin is envisaged for these granitoids, and the heterogeneous {varepsilon}Nd(t) values are inferred to have been acquired from the magma source region. Zircon Pb–Pb evaporation and U–Pb ages indicate widespread rift-related A-type magmatism at 1711–1660 Ma in the northern Delhi belt and also suggest a discrete older magmatic event at around 1800 Ma. The emplacement ages of the compositionally distinct A-type granitoid plutons, and virtually coeval granulite metamorphism and exhumation in another segment of the Aravalli mountains, further signify that part of the Aravalli crust evolved during a widespread extensional event in late Palaeoproterozoic time.

Key Words: Aravalli craton • Palaeoproterozoic • A-type granites • zircon chronometry • Nd isotopes






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