REAPPRAISAL OF THE DELHI STRATIGRAPHY IN THE AJMER-SAMBHAR SECTOR, NORTH-CENTRAL RAJASTHAN

The supracrustals occurring in the northern sector of the South Delhi Fold Belt (SDFB; main Delhi Synclinorium of Heron, 1953) between Ajmer -Pushkar valley and Sambhar Lake in north-central Rajasthan are classi fied into Anasagar migmatites and the overlying Ajmer Formation compri sing Taragarh quartzites and Kalyanipura arkose-pelite-greywacke seque nce. The Anasagar migmatites and paragneisses are intruded by latero g enic granite (1600 Ma) and post orogenic ultramafic and alkaline rocks . Four folding and two shearing movements characterize these rocks. Th ree metamorphic zones could be identified in these supracrustals with grade increasing towards west: staurolite-kyanite grade (middle amphib olite facies) in the eastern sector, sillimanite-muscovite grade (uppe r amphibolite facies) in the central sector, and orthopyroxene-plagioc lase and orthopyroxene-sillimanite grade (granulite facies) in the wes tern sector. The Anasagar and Ajmer supracrustals are deposited in an early Proterozoic ensialic basin in the Archaean BGC (Banded Gneissic Complex) protocontinent and differ from the other tectono-stratigraphi c units of the SDFB in respect of lithological organisation, metamorph ism arid magmatism besides the latter being decisively of Upper Proter ozoic age. The authors, therefore suggest a separate and older stratig raphic status to these supracrustals and delink from the rest of the S DFB stratigraphy,