Em comemoração do 20º Aniversário do Centro de Geofísica

Por: Dr. Anne Briais

Bureau Gravimetrique International, Obs. Midi-Pyrenees, Toulouse, France

Data: 27 de Junho

Hora: 14:30
Local: Anfiteatro 1 - CLAV

Abstract:

The high-resolution gravity maps derived from ERS-1 and Geosatsatellite geodetic missions reveal a set of small-scale lineations onthe flanks of slow to intermediate spreading mid- ocean ridges.Assuming that these lineations reflect the variations in crustalstructure induced by mid-ocean ridge axial discontinuities, we usethem to investigate how the discontinuities, and the segments theybound, appear, migrate, and disappear, on the flanks of theMid-Atlantic, Indian, and Pacific-Antarctic Ridges. The patterns ofthe gravity lineations appear to be very homogeneous over 500- to1000-km-large corridors bounded by large fracture zones. Close to hotspots, segments tend to migrate along axis away from hot spots, ortoward cold spots. Also, asymmetric spreading tends to keep sectionsof ridges closer to hot spots than normal spreading would. Theseobservations support the hypothesis that ridge segmentation and itsevolution are controlled by mantle dynamics. The results ofthree-dimensional numerical models of convection within the partiallymolten mantle beneath the ridge axis account for these observations.During the experiments the record of the ridge axis positions andcrustal production is used to compute synthetic maps of the isochronsand oceanic crustal thickness. Close to the ridge axis, the ascendingconvective flow consists of 80- to 100-km-long hot sheets orientedeither roughly parallel or orthogonal to spreading. Most ridgesegments fit with the top of hot upwelling sheets, while transienttransform faults coincide with the top of cold downwelling flows.Using the relationships between crustal lineations and convective flowin the models, we interpret the lineations described in thesatellite-derived gravity maps on the flanks of the Atlantic, Indian,and South Pacific plate boundaries.