Abstract:
Anisotropy of Magnetic Susceptibility (AMS) as a tool has been
explored here to investigate the nature of petrofabrics in Deccan
Volcanic Province (DVP) of west-central Indian region by
representative sampling in typical pahoehoe and rubbly pahoehoe
lava flows, dykes within flows, shear zone and the impact crater
units. The rock magnetic analysis indicate varying degree of
concentration of titanomagnetite compositions dominated by multi
domain (MD) to pseudo single domain (PSD) grains favoring shape
anisotropy of minerals that form primary fabrics. The pahoehoe
type lava flows shows planar oblate fabrics without any preferred
orientation of principle susceptibility axis (K1
) depicting crystal
settling (of magnetic grains) as chief mechanism of fabric
development. The rubbly pahoehoe type lava flow exhibit prolate
fabrics with well clustered maximum susceptibility axis within
horizontal to sub-horizontal planes depicting their response to
viscosity shear. The dykes show well clustered K1 parallel to it’s
plane locked during rapid contractional cooling. The sampling at
Lonar impact crater was unable to trace any clear fabric due to
impact/shock induced deformation and rather preserve the primary
fabrics. Further, the shear zone depict random fabrics demanding
more detailed and systematic sampling in both the cases. The
present investigation infer that the magnetic mineralogy and
magnetic fabric variations in the DVP are controlled by the flow
mechanism and style of cooling that is characteristic of the
given flow unit or dyke and any secondary or superimposed fabric
needs to be examined by critical sampling strategy. While more
detailed attempts are required to establish the AMS as a tool to
record various aspects including the flow dynamics and rate of
effusion in the vast terrain of DVP; the present approach is useful
to characterize and correlate the lava flow units and dyke
occurrences.
