Detecting the elevated crust to mantle section in the Kohistan-Ladakh Arc, Himalaya, from GOCE observations

The Kohistan Ladakh area in northeastern Pakistan is an exposed top to bottom crustal section, implying that high density rocks of the lower crust are at the surface. The new GOCE satellite observations improve the gravity field in this remote area, giving a new dataset for geophysical interpretation. We use the new data to determine the crustal thickness variations and to define the geometry of the overturned crustal columns constituting the base of the former island arc. For the first time the entire extension of the arc is traced with the help of the gravity field observed by GOCE. The entire arc generates a positive gravity signal up to 180 mGal, limited by two geological boundaries, the Main Karakorum Thrust at north, and the Main Mantle Thrust at south. The Main Karakorum thrustmarks the transition from the Indian to the Eurasian plate. The crustal thickness varies here between 40 and 70 km. The three geologic units that define the Kohistan arc, the South Plutonic Complex, the Chilas and Gilgit Complexes, occupy the upper crust, with depths increasing northwards between 14 and 44 km. There are not enough constraints to model the eastern part of the arc, the Ladakh, but the similarity of the gravity signal suggests that the thickness of the upper dense crustal units is similar.