LUMINESCENCE CHRONOMETRY OF TECTONIC LANDFORMS IN KACHCHH, W. INDIA : EVIDENCES OF LATERAL EASTWARD PROPAGATION OF THE KACHCHH MAINLAND FAULT

Consequent to continent-continent collision and flexing of the Indian lithosphere, the paleo-rift basin of Kachchh (Kutch), western India experienced several tectonic episodes along the major E-W faults. The 2001 Bhuj earthquake was the most recent evidence for a continued seismicity along Kutch Mainland Fault (KMF). The present contribution is a maiden attempt to reconstruct event chronology of the tectonic landforms in the northern hill range along KMF. Blue green stimulated luminescence (BGSL) ages on quartz extracts were used to infer the rates of river incision. Under a reasonable assumption that the climatic control on incision in such a hyper arid area was minimal.

The fluvial incision rates in the region bounded by N23^o19’- E69^o41’( Bhuj) to N23^o19’- E 70^o11’ (Devisar) were estimated using, a) channel fill deposits on incised bed rocks and b) valley fill terraces cutting across rising asymmetrical anticlines. BGSL ages indicate bed rock incision during 15 ka to 5 ka followed by aggradation between 5 to 0.5 ka and another incision since 500a. This implies two episodes of uplift, at 15 ka and 500a. Rates of Incision of ~1.5 mm/a on the strath bedrock terrace during 15 to 5ka, and 9.0mm/a during the past 500a on valley fill terraces are inferred. Geodetic measurements since 2001 have provided an uplift rate of 12mm/a in eastern KMF. A systematic decrease in the BGSL ages of channel fill deposits towards east [15ka(Bhuj) - 12ka (Jawaharnagar) - 7.6 ka (Khirsara)], indicate eastward propagating fault related folding of KMF. Deflection of drainage around the nose of plunging fold, the presence of water gaps and decrease in topographic relief further support this inference. The 2001 Bhuj earthquake was probably manifestation of this deformation, now active in the eastern zone of KMF.