| Abstract: | Seafloor at the Galapagos 95.5°W propagating rift (PR) has a varied morphological expression that can be spatially correlated with the predicted kinematic history of the PR. A median valley-like depression occurs near the tip of the growing ridge axis. To test if this bathymetry is a dynamic feature supported by mantle or lithosphere strength or if it is due to isostatically compensated crustal thickness variations, we use three-dimensional gravity modelling to constrain the crustal structure in this region, from data collected by Hey in 1979 and 1982. The gravity anomaly at the PR tip depression suggests that the tip depression is not caused by crustal thinning. The data are consistent with a stress-supported PR tip depression caused by asthenospheric along-axis flow into the growing ridge axis (Phipps Morgan and Parmentier 1]). In contrast to the tip depression, seafloor in the sheared zone of material transferred through transform migration from the Cocos to Nazca plate is anomalously shallow and has a pronounced regional 300–400 m tilt towards the growing ridge axis over the 20 km width of the sheared zone. The gravity data also suggest that the sheared zone is not compensated by crustal thickening. |
