| Abstract: | With an objective of better understanding the nature of India|Eurasia collision process, as manifest in the NW part of the Himalaya, gravity and GPS aided geodetic studies were carried out during the summers of 1994 through 1996. The area covered includes the Ladakh Himalaya, Indus suture zone (ISZ) and entire NW Himalaya between 74°～80° longitude and 30°～37° latitude. Gravity survey was carried out at 1～2km interval along Kiratpur—Leh—Panamik transect. Four different profiles viz., Kargil—Panikhar; Karu—Tangtse; Mahe—Sumdo and Nyoma—Kyon Tso were also taken. GPS was used, in fast|static mode for 3|d position determination of the gravity stations. The collected data were reduced to mean sea level using a new technique of terrain correction (Banerjee, 1998). The collected data was further combined with the published gravity data of SOI (Gulatee, 1956, Chug, 1978); ONGC (Raiverman et al., 1994) and Jin et al., 1994 to produce a new BA map for the NW Himalaya at 10mGal interval. Isostatic anomaly map of the region was also prepared using the BA map and ETOPO|5 global elevation data set. On the IA map, an isostatic high of about 80mGal is evident over the entire course of the higher Himalaya. This elongated pattern of the gravity high aligns itself over the exposed rocks of central crystallines where the average elevation is 4500m. This 80mGal isostatic high may have been caused due to the fact that isostasy does not strictly prevail in the higher Himalaya and these are in a state of under|compensation. This IA high has been interpreted in terms of upwarping in the Moho beneath the higher Himalaya. The IA analysis has also led to the depth of Moho to be 36～37km under the foothills, 60～65km under the higher Himalaya and 70～75km under the ISZ and beyond. Doubling of the crustal thickness is evident from the IA analysis and they are in general, in agreement with the DSS results of the Kashmir Himalaya. |
