SLOPE-DEVIATORY ALIGNMENT, STREAM NETWORK AND LINEAMENT ORIENTATION OF THE SABARMATI RIVER SYSTEM - NEOTECTONIC ACTIVITY IN THE MID QUATERNARY TO LATE QUATERNARY

The Gujarat alluvial plain located in the semi-arid zone is bounded by the arid Thar region in the north and the coastal/estuarine zone frin ging the Arabian Sea in the south. It has been built by the rivers ori ginating in the Aravalli Hills in the northeast. The drainages, with a n average length of about 300 km, generally follow the NE-SW regional slope. However, the Sabarmati River shows a flow deviating from the re gional slope and follows a N-S to NNE-SSW trend in the alluvial area. The slope-deviatory trend of the Sabarmati has been investigated with regard to Late Quaternary neotectonics, fluvial-aeolian interaction an d sea-level change. Lineament analysis indicates an E-W to WNW-ESE tra jectory of maximum principal stress, and that drainage is primarily co ntrolled by geodynamic processes. This is obvious from the corresponde nce in stress trajectories obtained from the lineament and drainage or ientations, respectively. Sub-surface data indicate pre-Neogene faulti ng in the basin. It is inferred that these faults have been reactivate d in the Mid- to Late Quaternary times. The slope-deviatory drainage o f the Sabarmati River is, to a large extent, the result of fluvial adj ustment to neotectonic reactivation in the region.