Fabric analysis in rocks of the Gadag region (southern India) - Implications for time relationship between regional deformation and gold mineralization

摘要

In this paper, the fabric in Archaean age massive metabasalts and granite from the Gadag region (Western Dharwar Craton, southern India) are identified using the anisotropy of magnetic susceptibility (AMS). The magnetic foliation in the rocks is dominantly NW-SE striking. This is inferred to have developed during regional D1/D2 deformation known to have affected the region, which was on account of NE-SW shortening. The plunge of themagnetic lineation varies fromNWto SE. This doubly plunging orientation is inferred to be a consequence of superimposition of NW-SE shortening (D3 deformation) over the earlier structure that is known to have resulted in dome-basin geometry in the surrounding metapelitic rocks of the region. Thus it is concluded that the massive rocks preserve evidence of superposed deformation that affected the region, which can be deciphered from the orientation of magnetic fabric data. The Gadag region comprises lode gold deposit (~2500 Ma in age), and field investigations show that the quartz veins are dilational with dominantly NW-SE (strike) orientation. The veins are inferred to have formed by dilation under NW-SE shortening during D3. It is envisaged that the NW-SE oriented fabric that formed in the metabasalt during D1/D2, channelized fluid flow, thus leading to vein emplacement during D3. It is concluded that gold deposition in the veins took place during D3, which is related to the final stages of cratonization of the Dharwar craton at ~2500 Ma.