Field and geochemical characteristics of the southwestern part of Sendra Ambaji Granitoid Belt, Rajasthan, India: Implication on its petro-tectonic evolution

Abstract

Neoproterozoic Sendra Ambaji Granitoid forms a NE–SW trending, ~360-km-long belt of intruding Mesoproterozoic metasedimentary rocks of the Delhi Supergroup along the Phulad Shear Zone in the South Delhi Fold Belt, northwest India. All work previously carried out on this granitoid is concentrated in the northern part of the belt, leading to difficulties in defining its petrogenesis and tectonic setting. To fill these knowledge gaps, a 350-km² area has been mapped in the southern extent of the belt between Sayra and Dhanbari. Field characteristics such as contact relationship, structure and geochemical characteristics are considered. Field studies show the presence of multiple cogenetic gneissose and non-gneissose but crudely foliated granitoid variants, which have been mapped separately. Three phases of ductile deformation and two phases of metamorphism in amphibolite facies akin to Phulad Ophiolite Suite are observed in all the granitoid variants. Refolding of gniessosity with the second deformation is observed in the granitoids and the Phulad Ophiolite Suite. Geochemical studies indicate that these granitoids are metaluminous to peraluminous, magnesian to ferroan, high K-alkaline fractionated I-type granitoids. Their composition is governed by partial melting of metasedimentary and mafic rocks of the continental crust at high temperature and subsequent fractionation, which has led to overlapping of S- and A-type granites on the I-type Sendra Ambaji Granitoid. The granitoids plot in both orogenic and post-collisional or within-plate fields. These signatures corroborate the inferences reached during field work, suggesting that Sendra Ambaji Granitoids were emplaced during the waning phases of orogeny in a subduction-related Andean-type continental arc setting. However, the emplacement of the granitoids continued post-orogeny. This collisional event is correlated with the amalgamation of the Rhodinia supercontinent.