Geochemical characterization and zircon U–Pb geochronology of the Tirodi Gneissic Complex, Central Indian Tectonic Zone (CITZ): constraints on petrogenesis, Proterozoic crustal evolution and tectonic setting

Abstract

The Tirodi Gneissic Complex (TGC) represents the basement sequence of the Central Indian Tectonic Zone (CITZ), underlying the Proterozoic supracrustal sequences of the Sausar and Betul Groups of rocks. Lithologically, the TGC constitutes a combination of pink and grey granitic gneiss assemblages, characterised by biotite-rich, hornblende-biotite-rich, and muscovite-biotite-rich granite gneiss. Compositionally, the TGC granitoids represent tonalite-trondhjemite-granodiorite to granite, and have calc-alkaline lineage with metaluminous to peraluminous characteristics. Geochemically, they dominantly belong to A2-type granitoids. Chondrite normalised REE ratios of La/Sm, La/Yb, La/Gd, and Gd/Yb indicate diverse LREE/HREE enrichment. Multi-element patterns for the TGC granitoids are characterised by light rare earth elements (LREE) and large ion lithophile elements (LILE) enrichment and depletion of high field strength elements (HFSE: Nb, P, and Ti) and strong positive Pb and Th anomalies. The observed negative anomalies for HFSE are attributed to diverse crustal/lithospheric sources, with some influence from K-feldspar, plagioclase and Ti-oxide fractionation. Sm–Nd data presents initial ¹⁴³Nd/¹⁴⁴Nd (t = 1.7 Ga) ratios (0.509898 to 0.510508), and ε_Nd (t = 1.7 Ga) is (+ 0.58 to -10.59), with T_DM model ages ranging from 2.11 to 2.95 Ga. Such a wide range of ε_Nd (t = 1.7 Ga), indicates heterogeneous crustal/lithosphere sources, which have probably experienced longer crustal residence times. Zircon U–Pb ages for individual TGC samples are 1506 ± 11 Ma (TG-01), 1534 ± 26 Ma (MU-5), 1675 ± 9 Ma (BT-4), 1724 ± 11 Ma (BT-3), 1730 ± 13 Ma (BT-4), and 1960 ± 2 Ga (Ms-2), respectively. These ages have probably recorded the key periods of the Columbia supercontinent's assembly, growth, and breakup. Geochemical and geochronological results suggest that the TGC granitoids have a crustal/lithospheric origin and are formed by partial melting of felsic sources in dominantly VAG (volcanic arc granite) and, to some extents, WPG (within-plate granite) settings.