Position of Dharwar Craton During Paleo-Neoproterozoic Period: Paleomagnetic Data of Cross-Cutting Dyke Swarms From Harohalli Area, Karnataka, India

One hundred oriented hand samples were collected during 2006 and 2008, from Paleo-Neoproterozoic diabase dykes from Harohalli area (Karnataka) belonging to the Archaean Dharwar Craton of Indian subcontinent. The area consists of several dyke swarms of different ages with cross-cutting relationships. Of them, the most conspicuous is the ~2.37 Ga (Halls et al., 2007; French et al., 2004) E-W trending quartz dolerite swarm. Among the samples collected, some are from fresh outcrops exposed in quarries and some from more weathered road-side outcrops or small field exposures. In few cases it is difficult to differentiate between the small exposures and the boulders in the field. Besides, very high Q-values obtained from petrophysical determinations for one of the sites indicate that the site is struck by lightning. Paleomagnetic and rock magnetic investigations carried out in the Laboratory for Solid Earth Geophysics of the University of Helsinki, including alternating field and thermal treatments for the samples, reveal the presence of two to three remanence components. The characteristic remanent magnetization component in the East-West trending quartz dolerite dykes is upward directed magnetization, which is strikingly similar to that reported by Halls et al. (2007) and Dawson and Hargraves (1994). Some sites reveal antipodal directions thus indicating field reversals. The characteristic component places India at high (southern?) paleolatitudes and the Dharwar Craton can be juxtaposed at 2.37 Ga with the Yilgarn Craton of Australia, where nearly coeval dykes (the Widgiemooltha swarm, 2.4 Ga) yield similar dyke trends in the reconstruction. This result may point to a long lived mantle plume under joint Dharwar-Yilgarn cratons. However, the origin of the other remanence components is less well understood. Further, a recent field study (2008) reveals that the N-S trending olivine bearing dyke swarm is in fact the oldest one in the area since it appears to be cut by the E-W swarm. In this paper, we present paleomagnetic data of cross cutting dykes of Harohalli area including baked contact tests, coupled with rock magnetic and petrophysical data in order to better define the APWP of the Dharwar Craton. In particular, we will seek evidences of possible block rotations or tiltings within the Dharwar craton in the light of feldspar clouding and paleomagnetic declination and inclination data. We also try to define the position of Dharwar craton in various proposed supercontinent assemblies during the Paleo-Neoproterozoic times.