3-D gravity inversion and rift stretching models are used in the Song Hong basin to determine the general configuration of the upper mantle and the mechanism for its formaton in the region. The basin approximately 200 km wide by 600 km in length, contains up to 14 km of sediments. The Bouguer gravity fiekd over the bvasin is relatively flat varying from 0 to-3t magal, suggesting high density material at the base of the crust. 3-D inversion was implemented converting modified Bouguer gravity anomalies and using cordell-Henderson gravity inversion method. Several rift stretcing modes were calculated using basement depths based on seismic studies and drill holes. The results of gravity modeling suggest that the Song Hong basin is a passive fit in which the failure of lithosphere is due to tension stress which introduces asthensopheric materials to the base of the crust. The tehsion reponsible for the rifiting is most probably linked to the collision between the India and Euroasia lithospheric plate.
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