Gravity anomalies, crustal structure and thermo-mechanical support of the Himalaya of Central Nepal

摘要: SUMMARY We use two gravity profiles that we measured across Central Nepal, in conjunction with existing data, to constrain the mechanical behaviour and petrological structure of lithosphere Himalayan collision zone. The data show (1) overcompensation foreland undercompensation Higher Himalaya, as expected from flexural support range; (2) a steep gradient order 1.3 mgal km x1 beneath suggesting locally steeper Moho; (3) 10 wide hinge southern Tibet. compare these 2-D model which Indian is flexed down by advancing front range sedimentation foreland. assumes brittle Coulomb failure nonlinear ductile flow depends on local temperature, computed steadystate thermal model. Moho fits seismological constraints consistent main trends observed Bouguer anomaly. It predicts an equivalent elastic thickness 40‐50 rigidity decreases northwards due weakening, resulting dip high range. Residuals at short wavelengths (over distances 20‐30 km) are interpreted terms sediment compaction (Dr=150 kg m x3 between Lower Middle Siwaliks); contact Tertiary molasse meta-sediments Lesser Himalaya MBT (Dr=220 ); Palung granite intrusion (Dr=80 ). Finally, if transformations (P, T) assumed, signature 250 predicted north essentially eclogitization lower crust, inconsistent data. conclude crust does not take place steady-state equilibrium assumption. show, however, might actually occur Tibet, where it could explain suspect eclogites subducted lithosphere.