Ion microprobe ²⁰⁷Pb/²⁰⁶Pb ages of zircons from the Bundelkhand massif, northern India: implications for crustal evolution of the Bundelkhand-Aravalli protocontinent

Abstract

²⁰⁷Pb/²⁰⁶Pb ages of zircon from gneissic rocks and granitoids representing all major lithological units of the Bundelkhand massif, northern India, have been determined using an ion microprobe. The presence of early Archaean granitic crust in this region is established from these ages. Ages for the Kuraicha and the Mahoba gneisses and associated metabasic enclaves suggest the oldest partial and metamorphic melting event in this region occurred at ≈3.3 Ga. The presence of younger gneisses with ages of ≈2.7 and ≈2.5 Ga suggests the existence of multiple protolith age components within the massif. Three major granitoid suites (hornblende-, biotite-, leuco-granitoids) were emplaced at ≈2.5 Ga within a time span of a few tens of millions of years. Felsic volcanism also occurred around this time. An age of 2.49 Ga for the youngest phase of leucogranitoid marks the time of overall stabilization of this massif. The geochronological history of the Bundelkhand massif appears to be remarkably similar to that of the basement complex of the Aravalli-Delhi orogenic belt, another prominent Archaean crustal block to the west of this massif. Geochemical features of the different rock types in these two regions are also very similar. We propose that these two apparently discrete blocks evolved as a single crustal unit with stabilization taking place at ≈2.5 Ga.