GRAVITY SURVEY AND STUDIES IN XIZANG PLATEAU REGION

An analysis of observed data of Bouguer gravity anomaly and free-air anomaly shows that there are anomalous gravity gradient zone, steeply varing zone of crustal thickness and a series of deep great fracture zones around Qinghai-Xizang plateau.Thus Qinghai-Xizang plateau can be deduced as a fault-block plateau.The recent collision-compressive zone of Eurasian plate with Indian plate is on the intermediate zone between the Himalayas and the Yarlung Zangbo river rather than the Yarlung Zangbo river fracture zone.The analytic results of repeated measuring data of gravity show that sensitive points of giavity field variation in Xizang region are on the Yarlung Zangbo river and its south, as well as on the deep-great fracture zone with north east strike in this region.The crustal movements, specially crustal activities since Cenozoic Era, in Xizang have been embodied mainly in the deep great fracture zone and its vicinity.