Record of 1.82 Ga Andean-type continental arc magmatism in NE Rajasthan, India: Insights from zircon and Sm–Nd ages, combined with Nd–Sr isotope geochemistry

Abstract

We document a Palaeoproterozoic Andean-type continental arc granitoid emplacement event in the northwestern segment of the Aravalli mountain range, NW India. Our study is focused on the Jasrapur pluton which is dominated by monzogranites with a subordinate amount of granodiorite and quartz monzodiorite. These rocks carry typical continental arc geochemical signatures, such as high-K calc-alkaline, mildly peraluminous, I-type and magnesian features, as well as high Rb and low Nb, Y and Rb/Zr ratios, decoupling between LILE and HFSE, and negative Nb–Ta and Ti anomalies. Conventional geothermobarometric estimates suggest high temperature (~ 800 °C) and pressure (≥ 600 MPa) conditions for the crystallisation of the Jasrapur granitoids. Whole-rock Sm–Nd isotope dating yielded an isochron age of 1800 ± 59 Ma, in good agreement with a zircon Pb–Pb evaporation age of 1821.7 ± 0.4 Ma, which we interpret to reflect the age of emplacement. A Ba-enrichment trend (400 to 1600 ppm), together with mantle-like initial Sr ratios (Sr i = 0.7060 ± 0.0007), suggest that the primary Jasrapur magma was generated from partial melting of a depleted mantle source enriched by slab-induced LILE fluids. Nevertheless, negative values of initial Nd (ε Nd(t) = − 5.01 ± 0.13) and a 2.6 Ga mean crustal residence age suggest the involvement of an Archaean component in the petrogenesis of Jasrapur magma. The eventual Jasrapur magma was generated from a zone of melting, assimilation, storage, and homogenisation, i.e. a MASHed zone at the base of an Archaean continental crust. Sr–Nd isotope mixing modelling, assessment of major element data based on various melts produced by experimental dehydration melting as well as comparison of the trace element data with those from the Central and Southern volcanic zones (CVZ and SVZ) of the Andes suggest that the Jasrapur magma underwent crustal contamination while traversing through a relatively thick continental crust. Appraisal of the REE patterns of the granitoids and tectonically similar and contiguous amphibolites signify that the granitoid magma was produced from a garnet-free but plagioclase-rich MASHed zone formed at a relatively shallow depth. Isotopic comparisons with other correlated events documented farther south in the central Rajasthan indicate a 1850–1822 Ma event of continental arc magmatism in the northwestern peninsular Indian shield which also corresponds in age to the amalgamation of the Palaeoproterozoic supercontinent Columbia.