MAGNETIC-ANOMALIES AND BASEMENT STRUCTURE AROUND VIZIANAGARAM, ANDHRA-PRADESH

Magnetic anomalies in an area of about 1500 sq km around Vizianagaram town in Andhra Pradesh bring out a shallow magnetic basement of charnockitic rocks, which is highly faulted. The magnetic basement exhibits horst and graben-like structures and broadly maintains conformable relations with the antiformal and synformal structures of the overlying khondalite suite of rocks. The development of these faults is attributed to the earlier folding of the Eastern Ghats and their refolding about a N-S axis to change their initial NE-SW trend to E-W and NW-SE in the northern part of Andhra Pradesh. The development of the horst-graben type structure is explained by movements of the faulted blocks along the fault planes at different stages of tectonic activity.