The Campo de Dalias GNSS Network Unveils the Interaction between Roll-Back and Indentation Tectonics in the Gibraltar Arc.

The Gibraltar Arc includes the Betic and Rif Cordilleras surrounding the Alboran Sea; it is formed at the northwest-southeast Eurasia-Nubia convergent plate boundary in the westernmost Mediterranean. Since 2006, the Campo de Dalias GNSS network has monitored active tectonic deformation of the most seismically active area on the north coast of the Alboran Sea. Our results show that the residual deformation rates with respect to Eurasia range from 1.7 to 3.0 mm/year; roughly homogenous west-southwestward displacements of the northern sites occur, while the southern sites evidence irregular displacements towards the west and northwest. This deformation pattern supports simultaneous east-northeast-west-southwest extension, accommodated by normal and oblique faults, and north-northwest-south-southeast shortening that develops east-northeast-west-southwest folds. Moreover, the GNSS results point to dextral creep of the main northwest-southeast Balanegra Fault. These GNNS results thus reveal, for the first time, present-day interaction of the roll-back tectonics of the Rif-Gibraltar-Betic slab in the western part of the Gibraltar Arc with the indentation tectonics affecting the eastern and southern areas, providing new insights for improving tectonic models of arcuate orogens.

Mantle flow and deep electrical anisotropy in a main gateway: MT study in Tierra del Fuego.

Asthenospheric mantle flow drives lithospheric plate motion and constitutes a relevant feature of Earth gateways. It most likely influences the spatial pattern of seismic velocity and deep electrical anisotropies. The Drake Passage is a main gateway in the global pattern of mantle flow. The separation of the South American and Antarctic plates since the Oligocene produced this oceanic and mantle gateway connecting the Pacific and Atlantic oceans. Here we analyze the deep crustal and upper mantle electrical anisotropy of its northern margin using long period magnetotelluric data from Tierra del Fuego (Argentina). The influence of the surrounding oceans was taken into account to constrain the mantle electrical conductivity features. 3D electrical models were calculated to fit 18 sites responses in this area. The phase tensor pattern for the longest periods reveals the existence of a well-defined NW-SE electrical conductivity anisotropy in the upper mantle. This anisotropy would result from the mantle flow related to the 30 to 6 Ma West Scotia spreading, constricted by the subducted slab orientation of the Pacific plate, rather than the later eastward mantle flow across the Drake Passage. Deep electrical anisotropy proves to be a key tool for a better understanding of mantle flow.