We present a study of the Gyangarh and Anjana granitoids in the Aravalli Craton, northwestern India, with new data on their whole-rock geochemistry, U-Pb zircon and U-Th-total Pb monazite geochronology and structures and microstructures. These granitoids are monzogranites with metaluminous and calc-alkalic geochemical characters. They show negative Eu anomalies with depletions in Sr and Ti, indicating fractionation of plagioclase and Fe-Ti oxides from their parental magmas. U-Pb zircon dating of granitoids yielded crystallization ages of 1776 ± 35 Ma to 1709 ± 29 Ma, indicating that the plutons were emplaced during the late stages of the Aravalli orogeny. These plutons have been variably deformed and show shallow- to moderately dipping mylonitic foliations (<40°) with shallow (<30°) NW- to NE-plunging stretching lineations (SL1). The pole distribution of the mylonitic foliation (S1) and lineation (SL1) data indicates that the gentle mylonitic foliations have been overprinted by steep (>65°), NE-SW-striking S2 mylonitic foliations. The kinematic indicators suggest that the D1 and D2 deformations were associated with dextral-normal and sinistral-reverse senses of shearing, respectively. Monazite dating of texturally constrained grains shows that the pluton experienced intense mylonitization (D1-S1; 1653 ± 30 Ma) during the waning stages of the Aravalli orogeny. Later, these plutons experienced a second episode of mylonitization (933 ± 11 Ma to 897 ± 9 Ma) due to sinistral-reverse shearing (D2-S2) during the late stages of the Delhi orogeny. These new results show that the Gyangarh and Anjana plutons record signatures of two major orogenies that have shaped the Sandmata Complex (Aravalli Craton) in the Palaeoproterozoic.

This work describes the mineralogy of dolomite carbonatite occurring at the Newania carbonatite complex, Rajasthan, north-western India. The mineralogy records the textural and compositional features of magmatic and post-magmatic stages of carbonatite evolution. Ferroan dolomite is the principal constituent and displays variable degrees of deformation, ranging from brittle-to-ductile deformation regimes. Apatite exhibits textural and compositional evolutionary trends from early-to-late stages of carbonatite evolution. Two varieties of amphibole are reported for the first time from this complex, ferri-winchite and cummingtonite; the former is magmatic and the latter is metamorphic in origin. The columbite–tantalite-series minerals are columbite-(Fe), and their paragenesis evolves from composite grains with pyrochlore to individual crystals. Pyrochlore is magmatic with U–Ta–Ti-rich compositions and shows evolution from calciopyrochlore to kenopyrochlore, followed by alteration during late-stages of carbonatite evolution. Monazite and baryte constitute the post-magmatic mineral assemblage; the former is hydrothermal and crystallised after precursor apatite, whereas the latter is associated exclusively with columbite–pyrochlore composites. On the basis of the mineralogy of the carbonatite, it is concluded that the parent magma was generated by low-degree partial melting of magnesite–phlogopite-bearing peridotite.

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 εNd 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 εNd(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.