Zircon-monazite geochronology, petrogenesis and deformation of the Gyangarh-Anjana monzogranites (Aravalli Craton): records of two Proterozoic orogenic events in Northwestern India

Abstract 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 (SL 1 ). The pole distribution of the mylonitic foliation (S 1 ) and lineation (SL 1 ) data indicates that the gentle mylonitic foliations have been overprinted by steep (>65°), NE-SW-striking S 2 mylonitic foliations. The kinematic indicators suggest that the D 1 and D 2 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 (D 1 -S 1 ; 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 (D 2 -S 2 ) 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.