GANGES BASIN GEOMETRY RECORDS A PRE-15 MA ISOSTATIC REBOUND OF HIMALAYA

Abstract

The Tertiary continental strata of the Himalayan foreland basin are subdivided into two groups, but the meaning of this subdivision was previously unclear. From the analysis of drill holes, seismic lines, dated sections, outcrops, and balanced cross sections, we find that the southward migration rate of the depositional pinch-out of the younger group is 19 ± 5 mm/yr and equals the Himalayan shortening rate. This equality shows that the flexural foreland basin development is mainly controlled by the motion of the thrust load. The long-term pinch-out migration rate was slower for the older synorogenic group. Erosion locally occurred at the end of its deposition, due to tectonic reactivation of lineaments of the Indian shield. We suggest that this change in the basin development is linked to the detachment of the subducted Indian lithosphere that decreased the slab pull and increased the mean compressive stress within the Indian plate, whereas the plate motion remained constant. The most important implication of our work is that the associated isostatic rebound could have increased the Himalayan elevation prior to 15 Ma. © 2006 Geological Society of America.