The Ganges basin geometry records a pre-15 Ma isostatic rebound of Himalaya

7 The Tertiary continental strata of the Himalayan foreland basin are subdivided in two 8 groups, but the meaning of this subdivision was previously unclear. From the analysis of drill9 holes, seismic lines, dated sections, field outcrops and balanced cross-sections, we find that the 10 southward migration rate of the deposition pinch-out of the younger group is 19 ± 5 mm/yr and 11 equals the Himalayan shortening rate. This equality shows that the flexural foreland basin 12 development is mainly controlled by the motion of the thrust load. The long-term pinch-out 13 migration rate was slower for the older syn-orogenic group. Erosion locally occurred at the end 14 of its deposition, due to tectonic reactivation of lineaments of the Indian shield. We suggest that 15 this change in the basin development is linked to the detachment of the subducted Indian 16 lithosphere that decreased the slab pull and increased the mean compressive stress within the 17 Indian plate, whereas the plate motion remained constant. The most important implication of our 18 work is that the associated isostatic rebound could increase the Himalayan elevation prior 15 Ma. 19