Long-term variability of Earth’s early Dipole magnetic field (palaeointensity; PI) is a complex internally driven phenomenon. The first data from the largest Cretaceous flood basalt province on Earth, the ~65–66 Ma Deccan basalt within a thick (1250 m) unbiased stratigraphic section down to the basement, recovered from a drill hole of the Koyna Deep Scientific Drilling Project in the Western Ghats, India are analysed. Out of 76 samples covering 19 flows, only 34 samples from nine flows yielded PI data. None of the flows represent transition field, eight lava flows (26 samples) provide a reliable mean palaeointensity of 7.30±3.45μT. The calculated mean VDM is 1.46±0.69 ×1022 Am2 (range: 2.19–0.28 ×1022 Am2). The results highlight (a) Dipole moment during the end Cretaceous Deccan eruption is the lowest in the whole of Cretaceous while dipole moment is generally lower at onset/termination of Cretaceous Normal Superchron relative to mid-superchron times (b) lack of perfect inverse relation between dipole moment and field reversal rate in contrast to many studies invoking coupling between the two and (c) a cause and effect relationship between CMB heat flux and the dipole low, supporting the predictions of the numerical models; large igneous provinces are manifestations of this activity on the surface of earth.
Figure Caption: Distribution of VDM data during the Cretaceous period. The timing of mantle plumes of the Cretaceous responsible for the major large igneous provinces marked as A, B, C and D: A denotes the Reunion related Deccan flood basalt (and near synchronous ~62 Ma North Atlantic Tertiary Volcanic Province), B denotes the Marion plume related Madagascan igneous province (and near synchronous ~ 90 Ma Ontong Java plateau), C denotes the Kerguelen plume related Rajmahal volcanism and D denotes the Tristan da Cunha plume related Parana basalts. The ages of these LIPs are shown with error bars. The grey shade demarcates the CNS.
Radhakrishna T, Asanulla R. Mohamed, Venkateshwarlu M, & Soumya G. S.; 2020. Low geomagnetic field strength during End-Cretaceous Deccan volcanism and whole mantle convection. Scientific Reports | (2020) 10:10743 | https://doi.org/10.1038/s41598-020-67245-6, published online on 1st July, 2020.