Palaeomagnetic dating of Sankra dyke swarm in the Malani Igneous Suite, Western Rajasthan, India

The Malani Igneous Suite is a heterogeneous suite comprising acid lava flows and intrusions divided into three phases of igneous activity, the youngest of which consists of all dykes identified within the Sankra pluton. The dykes in the Sankra pluton have been divided into five sub-phases on which radiometric dates are not available. Hence the sequence of magmatic emplacement is not known. We have undertaken a palaeomagnetic study of four dykes, namely the aplite, granite porphyry, dolerite and gabbro types representing the first, third and fifth sub-phases. The characteristic remanent magnetic (ChRM) directions of these dykes have been recovered by detailed laboratory studies using AF and thermal demagnetization methods on the oriented samples collected from these dykes. The virtual geomagnetic poles of these dykes, when plotted on the apparent polar wander path of the Indian subcontinent, assign their ages between 750 and 60 Ma. The ChRM direction in the aplite dyke is similar to that of the Malani Rhyolite and a granitoid body from Seychelles Islands. Thus, these three results indicate the formation of a tectonic trio with Madagascar towards the western side of the Neoproterozoic Rodinia supercontinent, and also confirm the age of the aplite dyke.