Mundwara Alkali Igneous Complex, Rajasthan, India: Chronology and Sr Isotope Systematics

Six whole rock samples have been dated by ⁴⁰Ar/³⁹Ar method to ascertain the emplacement time of the Mundwara Alkali Igneous Complex, Rajasthan, India. The dated samples include four from the Musala hill and one each from Mer and Toa hills of the complex. Out of these, only two syenite samples. viz. MR 86/4 and MR 86/7 from the Musala and Mer hills, respectively, have given plateaus at 64 Ma, while the remaining samples have exhibited saddle shaped spectra owing to the presence of excess argon. However, similar isochron ages of about 70 Ma obtained from a basalt (Musala hill) and a gabbro (Toa hill) by linear regression of all the data points might suggest initiation of igneolls activity at Mundwara around 70 Ma ago.

⁸⁷Sr/⁸⁶Sr ratios of this suite range from 0.70385 to 0.70551 indicating its derivation from a mantle source.