INDIA AND SOUTH CHINA IN THE TONIAN: NEW CONSTRAINTS FROM THE HAROHALLI ALKALINE PROVINCE

The position of India in the supercontinents of Rodinia and Columbia is enigmatic and India is typically relegated to the margins of those supercontinents. A recent compilation of paleomagnetic data from India lists only two poles for Columbia (~1.8-1.4 Ga) and single poles for assembly and breakup of Rodinia. In many reconstructions, India remains linked to the East Antarctic craton and Australia in an East Gondwana configuration (Li et al., 2008). Links between India and South China in the Rodinia supercontinent were based on stratigraphic similarities and isotopic/detrital zircon studies (Jiang et al., 2003; Wang et al., 2017). Other reconstructions place India and South China in proximity although separated from one another by another craton or micro-continents (Li et al., 2008; Chang et al., 2022, Li et al., 2023). India’s location in these reconstructions relied on the ~770 Ma MIS suite pole (Meert et al.,2013). A new U-Pb titanite age of 820 ± 15 Ma is recorded from a lamprophyric dyke in the Harohalli alkaline province (India). Rb-Sr and K-Ar ages are similar to the U-Pb age, but Pradhan et al. (2012) obtained a much older U-Pb (1192 Ma) age from one of the dykes. Because the dated dyke in that study did not yield paleomagnetic data, caution was urged in using the Harohalli dykes paleomagnetic pole. We have reviewed the paleomagnetic data in those 3 studies and calculated an updated pole for the alkaline dykes at 36.1° N, 84.0° E (A95=11.3°, K=30). Coeval data from South China at 824 Ma (Yanbian Dykes-A=YA pole) and 770 Ma (Yangtze dykes=YD) can be used to reconstruct India and South China. The fit between the two pairs of similar age poles from both cratons is excellent (HD-YA Bayes error=.482 and MIS-YD Bayes error=.384; Meert and Santosh, 2022). If we assume that South China and India were fellow travelers during the 825-770 Ma interval, then we can use other poles from South China to evaluate the drift rate of both cratons. We perform a bootstrap calculation for pole positions and Monte Carlo age simulations to evaluate apparent polar wander (APW) rates and latitudinal drift rates. Rates of APW range from 20-36 cm/year indicating that true polar wander should be considered in addition to normal plate motion. We also examine paleomagnetic data from Laurentia during this same interval which suggests a large separation between Laurentia and India-South China by at least 820 Ma.