The Late Palaeoproterozoic Mayong granitoids of Assam constitute an important component of the continental crust and the Basement Gneissic Complex in the northern extension of the Shillong Plateau, north‐east India. The basement rocks of Shillong Plateau are considered as a continuation of the Central Indian Tectonic Zone. In this study, emphasis is given on the new zircon U–Pb age, Hf isotopic composition, and the tectonic implication of Late Palaeoproterozoic Mayong granitoids. The Mayong granitoids are essentially composed of quartz—K‐feldspar—plagioclase—biotite—hornblende as major minerals and titanite—zircon—allanite—bastnaesite—apatite—ilmenite as the accessory mineral phase. They show typical geochemical characteristics of A‐type granites, such as high silica (average 71.86 wt%), alkalies (average 8.01 wt%), Rb, Zr, Nb, Ga, and rare earth elements (except Eu); high FeOt/MgO and Ga/Al ratios, and low CaO, MgO, Ba, Sr, P, Eu, and Ti concentrations. Laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating indicates that they were emplaced at ~1,687 ± 35 Ma during the large‐scale magmatism of Late Palaeoproterozoic to Early Mesoproterozoic periods. Their zircon Hf model (TDM2) ages (1,833–2,257 Ma) in conjunction with trace elemental characteristics suggest that they were generated by the reworking/recycling of Early Palaeoproterozoic crust in an intraplate extensional tectonic environment. Thus, we conclude that these A‐type Late Palaeoproterozoic Mayong granitoids of the Shillong Plateau probably have a close genetic linkage with the magmatic event of the Columbia Supercontinent cycle during 1,687 ± 35 Ma.

Intrusive granitoid bodies and quartzofeldspathic gneiss outcrops in the Guwahati and Mayong areas are considered part of the northern extension of the basement gneissic complex of the Shillong Plateau. They are medium to coarse-grained porphyritic granitoids essentially composed of quartz, K-feldspar, plagioclase, biotite, hornblende, sphene, magnetite, apatite, zircon, allanite, and bastnaesite in different proportions. Mineralogical characteristics of these granitoids reveal that they are monzogranite. The biotites are re-equilibrated in Guwahati granitoids whereas they are primary in Mayong granitoids. Ti-in biotite, Al-in hornblende and mineral assemblage biotite-K-feldspar-magnetite were used to determine temperature, pressure and oxygen fugacity during the crystallization of parent magmas. The Guwahati granitoids crystallized and re-equilibrated at temperatures ranging between 602°C and 752°C (avg. 685°C) with pressure (5.2 - 5.6 kbar, avg 5.4 kbar) from low oxidized magmas (log fO2 -16.33 to -14.36 bar), buffered below FMQ to within NNO. The Mayong granitoids crystallized at temperatures range 694°C to 715°C (avg. 705 °C) with pressure (4.7 to 5.1 kbar, avg. 5 kbar) under reduced oxidized condition (log fO2 -17.88 to -17.62 bar) buffered below FMQ. The calc-alkaline nature, low to moderate oxygen fugacity and high H2O (4.5-7.4 wt%) content suggests that Guwahati granitoids emplaced in subduction-related tectonic setting whereas alkaline nature, reduced oxygen fugacity and low content of H2O (2.15 wt%) suggest anorogenic tectonic setting for Mayong granitoids. Also, from the estimated pressure and depth of emplacement conditions it suggests that both the granitoids are mid-level plutons.