Borehole magnetic fabric anomalies in KBH 07 Deccan basalt core from Deep Continental Drilling, western Maharashtra, India

The anisotropy of magnetic susceptibility (AMS) record generated from 112 levels in 1248 m long KBH 07 borehole up to the basement in Deccan Volcanic Province of Koyna region depicts episodic variation in the magnetic fabrics. Anomalies in the AMS parameters: volume susceptibility (K), degree of anisotropy (Pj), shape factor (T), degree of lineation/foliation (L/F), inclinations of principle susceptibility axes (Kmax and Kmin) are inferred along with previously published rock magnetic data for the KBH 07. A major change observed at ~600 m level based on magnetic mineralogy and fabrics, density and lava thickness pattern is attributed to shift in magmatic compositional trends in agreement with the high-Mg to low-Mg magma reported previously in the same core (Banerjee and Mondal 2021). Further, the higher-order anomalies depict smaller episodes influencing the fabrics possibly due to differential dynamic viscosities governed by composition in addition to cooling trends. Whereas the major trends can be assigned to compositionally controlled viscosities and hence can be correlated to larger stratigraphic intervals based on the AMS studies.