Geochemistry and U–Pb CHIME Ages of Tonalite–Trondhjemitic–Granodioritic (TTG) Gneiss from the Central Bundelkhand Craton, India: Implication for the Presence of Paleoarchean Crust from Easternmost Exposed Boundary of the Craton

Abstract

AbstractThe present study is pertaining to the field occurrence, petrology, and geochemistry of TTG gneiss associated with the central greenstone complex of Bundelkhand craton and new U–Pb CHIME ages of TTG gneisses from eastern most exposed part of the Central Bundelkhand terrane. The present data compiled with published database are used for the determination of nature of multiple TTG magmatic episodes and their role in overall evolution during Paleo–Mesoarchean crust of Bundelkhand craton. TTG gneiss occurs in association with metavolcanic rocks as well as enclaves within (ca 2.5 Ga) granitic intrusions. The TTG gneisses have wide range of SiO2 (62.0–77.27), Al2O3 (11.65–17.89), MgO (0.24–2.43), CaO (0.76–4.78), Na2O (3.33–6.34), and K2O (0.38–5.62). These rocks have high Na2O values relative to CaO and K2O with consistent low (K2O/Na2O) ratio. In primitive mantle-normalized diagram, LIL element shows enriched nature, while HFS elements show depletion. Based on HREE concentration, the compiled TTG gneisses data from Central Bundelkhand terrane are further classified into three groups as low HREE (TTG-I), high HREE (TTG-II), and medium HREE (TTG-III). The protoliths of TTG gneisses are interpreted to have been formed in subduction-related tectonic setting at the garnet stability P–T field (TTG-I), plagioclase stability field (TTG-II), and intermediate depth (TTG-III). We suggest that the source material for the TTG-I was rutile-free amphibolite and/or Eoarchean tonalite, whereas for the TTG-II and the TTG-III it was enriched mafic source. Chemical Th–U total Pb isochron (CHIME) age of TTG gneiss from eastern most part of the Central Bundelkhand terrane for two samples give 3242 ± 168 Ma and 3181 ± 118 Ma age, respectively. These ages are the first report of Paleo–Mesoarchean TTG crust from eastern most exposed areas of the Bundelkhand craton and suggest extension of linear tract of TTG gneisses from the Babina, Mauranipur, and Mahoba up to Chitrakoot area, stretching the earlier known exposed limit of Paleoarchean crust by about 50 km eastward. Geochronological database suggests that the TTG-I were formed during 3.59–3.40 Ga and the TTG-II between 3.40 and 3.20, while the TTG-III magmatism occurred during ~ 2.7 Ga.KeywordsTonalitic–Trondhjemitic–Granodioritic (TTG)PalaeoarcheanCHIME Ages