STABILIZATION OF THE ARAVALLI CRATON OF NORTHWESTERN INDIA AT 2.5 GA - AN ION MICROPROBE ZIRCON STUDY

In order to establish the stabilization age of the Aravalli Craton of northwestern India, we have used an ion microprobe to measure Pb-207/P b-206 ages of zircons from six samples collected from the southern Ara valli Mountains. Our analyses gave precise results for four granitoids whose minimum crystallization ages ranged between 2562 +/- 6 and 2440 +/- 8 Ma (1 sigma). A single sample of gneiss gave an age of 2502 +/- 4 Ma, which is unexpectedly younger than an age of 3281 Ma which we p reviously obtained from another gneissic sample. We interpret the 2502 Ma age as the time of emplacement of the sample's igneous protolith, suggesting that the Mewar Gneiss contains multiple metamorphic compone nts of differing ages. Based on our data, we conclude that the souther n segment of the Aravalli Craton had broadly stabilized by similar to 2.5 Ga. This stabilized landmass formed the basement on which the youn ger Aravalli Supergroup was unconformably deposited. This study repres ents the first application of a small geometry ion microprobe for rout ine geochronology.