Paleomagnetism of ca. 2.3 Ga mafic dyke swarms in the northeastern Southern Granulite Terrain, India: Constraints on the position and extent of Dharwar craton in the Paleoproterozoic

Abstract

The pole positions reported for the mafic dykes occurring in the northeastern Southern Granulite Terrain and easterly trending dykes of Dharwar craton are alike while their ages differ by ca. 700 Ma confounding tectonic reconstruction. To resolve the discordance and to constrain the position of the Indian continent in the Proterozoic, paleomagnetic and geochronological studies have been carried out on the mafic dyke swam in the northeastern Southern Granulite Terrain. Two distinct pole positions are obtained, one from the group of Tiruvannamalai dykes as 27.7°S, 231.5°E (dp, dm = 12°, 14°) with corresponding mean declination (Dm) and inclination (Im) as 125° and −73.8° (κ, α95 = 22, 7.6°) respectively, and second from the East Coast Dykes as 2.32°S, 188.2°E (dp, dm = 5°, 8°) with corresponding mean Dm and Im as 88.9° and −33.8° (κ, α95 = 48, 7.1°) respectively. The Remanent Efficiency of Magnetization values between 0.01 and 0.08 suggest that the dykes have been cooled through Curie temperature of magnetite which is the carrier of magnetization. The baked contact test confirms that the Characteristic Remanent Magnetization is the primary magnetization. The Sm–Nd mineral-whole-rock isochron, from one of the Tiruvannamalai dykes, yielded an age of 2318 ± 60 Ma (MSWD = 1.9). This age is the time of intrusion of the Tiruvannamalai dykes and is similar, within errors, to the age of dykes in the Dharwar craton. Thus, the contiguity of Dharwar craton with the Northern Block of Southern Granulite Terrain, as early as 2.3 Ga ago, is established. The pole position thus obtained corresponds to a high-latitudinal position of Dharwar craton during early Paleoproterozoic.