Title: Regional deformation imprints from anisotropy of magnetic susceptibility data – an example from the Raichur Schist Belt (Dharwar Craton, India)

Santu Biswas1, Manish A Mamtani1, Agnes Kontny2, Christoph Hilgers2

1Department of Geology and Geophysics, Indian Institute of Technology (IIT), Kharagpur; 2Institute of Applied Geosciences, Karlsruhe Institute of Technology (KIT)

Event: GeoKarlsruhe 2021

Date: 2021

DOI: 10.48380/dggv-hg3z-k697

The Raichur Schist Belt (RSB) is a NW-SE trending late-Archaean greenstone belt that forms part of the supracrustal units lying over an older gneissic basement. Granites (ca 2.5 Ga) occur in the vicinity of the RSB. The metavolcanics and granites are both massive and lack a field foliation and/or lineation. To work out the time-relationship between emplacement, fabric development and regional deformation of the granite vis-à-vis metavolcanic rocks and regional deformation, we performed Anisotropy of Magnetic Susceptibility (AMS) studies. Mean magnetic susceptibility (Km) of the metavolcanics varies between 843 µSI and 57800 µSI units, while in the granite it is between 6.88 µSI and 45000 µSI units. Microstructural studies reveal that the rocks are deformed and AMS is mostly controlled by paramagnetic phases. Temperature-dependent magnetic susceptibility studies carried out so far establish that samples with Km>1260 µSI contain multidomain magnetite. In the metavolcanics, mean orientation of magnetic foliation is NNW-SSE; this is similar to D1/D2 regional fabric of Dharwar Craton. The magnetic lineation is doubly plunging (direction varying from NNW to SSE). This is a manifestation of D3 superposed on D1/D2 fabric in the metavolcanics of RSB inferred from magnetic fabric, the mesoscopic field evidence for which is lacking. Similar superposed deformation is also implied from the AMS data of granites. The region is replete with quartz veins and their orientation analysis with respect to the magnetic fabric is expected to provide further details about the kinematics of the rocks.

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