New age, geochemical and paleomagnetic data on a 2.21Ga dyke swarm from south India: Constraints on Paleoproterozoic reconstruction

摘要

Geochemical, paleomagnetic and Sm-Nd whole rock-mineral isochron age data are presented for a ～450km-long N-S striking mafic dyke swarm from the Dharwar craton, southern India. Dykes in this swarm are basaltic tholeiite in composition and despite traversing diverse Archean rocks display limited compositional heterogeneity along their entire outcrop. Two whole rock-mineral Sm-Nd isochrons from one of these dykes yield ages of 2173±43Ma and 2190±51Ma (2σ) respectively. These ages are consistent with recently reported U-Pb ages of 2209.3±2.8Ma and 2220.5±4.9Ma for two other dykes within the craton that show a similar trend and chemical composition (French and Heaman, 2010), suggesting emplacement of this swarm close to 2210±10Ma. Paleomagnetic directions obtained from fifteen sites along the length of this swarm are all similar within errors despite dissimilar orientation between dykes towards the northern end of the swarm, with a grand mean of D_m=239° and I_m=-64°, corresponding to a paleopole at lat. 32°S; long. 302°E (dp=8, dm=10). This Paleoproterozoic pole from the Dharwar has coeval poles from the Slave, Superior and Rae provinces and allows a Paleoproterozoic reconstruction of these cratons. Our reconstruction at ～2210Ma shows that all these cratons could have been located within about 30° of each other, with Slave and Dharwar being remarkably closer (<10°). However, lack of reliable Neoarchean paleomagnetic data from the Dharwar inhibits tracing its ancestry to either of the Neoarchean Supercratons: Sclavia or Superia.