Charnockitic Rocks of Tinnevelly District, Madras

The charnockitic rocks of the Tinnevelly district are conformable in strike and dip with the enclosing gneissic rocks and nowhere show cross-cutting intrusive relationship. The geological structure consists of an earlier period of folding about a NW-SE axis, followed by a second stage cross-folding about a NNW-SSE axis, and discordance of rock types as well as structural elements in the north-east part of the district by a zone of thrust. The charnockitic rocks thus appear to have been subjected to two periods of deformation, granitic intrusion and metamorphic episodes.,

The mineralogical compositions, lithological associations, mutual field relationships and structural history of the district, suggest that Tinnevelly charnockitis represent a geosynclinal association of sediments, basic volcanics and intrusives, folded and refolded during possibly two periods of orogeny, accompanied by granitic and migmatitic activity and deep-scated plutonic palingenetic recrystallisation.