The diversification of granitoids and plate tectonic implications at the Archaean–Proterozoic boundary in the Bundelkhand Craton, Central India

The Bundelkhand Craton in Central India holds a large Archaean granitoid complex consisting of cores of TTG (tonalite–trondhjemite–granodiorite) gneisses of island arc or oceanic origin surrounded by abundant younger high-K calc-alkaline granitoids. Major and trace element groupings and ion probe U–Pb zircon datings of the groups show a time gap of 130 Ma between the main formation episodes of the TTGs (3.5/3.3–2.7 Ga) and the emplacement of the first high-K granitoids (2.57–2.54 Ga). Based on their geochemical diversity, the high-K calc-alkaline granitoids can be divided into low-silica high-magnesium (LSHM) granitoids such as sanukitoids and Closepet-type granitoids, and high-silica low-magnesium (HSLM) monzogranites with low-HREE and low-Eu subgroups. The former group points to mantle or mixed mantle and crustal sources, and the latter to pure crustal sources. All the varieties of the high-K granitoids formed within a narrow time span, which indicates large-scale partial melting and fluid activity in the mantle and crust, possibly resulting from a slab breakoff or delamination at the margin of an Archaean TTG continent.