Three-dimensional gravity inversion model of the deep crustal structure of the central drake passage (Shackleton Fracture Zone and West Scotia Ridge, Antarctica)

Abstract

[1] Gravity and bathymetric data collected by the Spanish R/V Hesperides over the Shackleton Fracture Zone (SFZ) and the West Scotia Ridge (WSR) were used to invert for the three-dimensional (3-D) structure of the deep crust. Data from the Global Gravity Grid and Global Seafloor Topography (GGSFT) were also employed to enlarge the cruise area. The merged data were analyzed to determine the 3-D deep structure by numerical inversion. Water layer contribution to the gravity anomaly was eliminated, taking into account the bathymetry. Spectral analysis of the reduced data yielded mean crust-mantle interface (CMI) depths of 10.5 +/- 1.2 km. Inversion of the regional anomaly gave a 3-D detailed geometry of the CMI, which generally agrees with the 2-D models established along profiles where gravity data and multichannel seismic lines are available. The WSR shows an asymmetrical structure with a reverse fault located southeastward to the central valley. This fault was developed, probably, as a consequence of the NW-SE compressive deformations, which occurred following the spreading. The 3-D view shows that the SW end of the spreading axis was affected more intensely by the compression. The SFZ represents an active sinistral transpressive fault zone of the Scotia-Antarctica plate boundary and shows crustal thickening related to bathymetric highs. The crustal thinning detected at the intersection with the inactive WSR suggests a complex interaction between these two structures.