Formula omitted] zircon ages and the evolution of the Singhbhum Craton, eastern India: an ion microprobe study

Abstract

We used an ion microprobe to measure 207 Pb/ 206 Pb ages of single zircons from four key lithologies from the Singhbhum Craton of eastern India. Detrital zircons from the oldest recognized sedimentary sequence of the craton (the Older Metamorphic Group) yielded 3.5–3.6 Ga ages, indicating that crustal formation had already been initiated by 3.6 Ga in this region. This data also established an older limit of 3.5 Ga for the age of sediment deposition. The first appearance of extensive continental crust in the Singhbhum region, marked by the emplacement of the Older Metamorphic Tonalite Gneisses, is dated at ∼3.44 Ga. Our data from both of these units reveal that a 3.2 Ga event induced overgrowths within each of these pre-existing zircon populations. We determine an age of 3328±7 Ma for the Singhbhum Granite (phase II), the most widespread of this granite's three phases. The emplacement of the two phases of the Mayurbhanj Granite, marking the youngest major episode of acid plutonism in this craton, took place in rapid succession at ∼3.1 Ga, marking the broad-scale stabilization of this terrain.