Researchers Target a continental transform Fault in Tierra del Fuego.

LODOLO, E.; M. MENICHETTI; A. TASSONE; R. GELETTI; P. STERZAI; H. LIPPAI; J. L. HORMAECHEA

EOS Transactions AGU

American Geophysical Union AGU

Lugar: Washington; Año: 2002 vol. 83 p. 1 - 6

A comprehensive suite of field surveys was carried out by a team of Italian and Argentinean scientists in the Tierra del Fuego region, the southern tip of South America, to investigate the 600-km-long Magallanes-Fagnano fault system (MFS), a transform-type margin developed on continental crust (Figure 1). The identification and analysis of the morphological and structural elements related to the MFS, and the understanding of mechanisms of slip along the fault, are the principal objectives of an ongoing project called TESAC (Tectonic Evolution of the South America-Scotia plate boundary during the Cenozoic), jointly managed by the Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS) of Trieste, and the Dpto. de Geologia, Universidad de Buenos Aires. The MFS, which represents one of the major segments of the South America-Scotia plate boundary, runs from the western arm of the Magallanes Strait to the Atlantic offshore, and substantially splits the Isla Grande, the main island of Tierra del Fuego, in two continental blocks. An integral part of the project is focused on the pull-apart basins, the elongated depocenters which generally form in correspondence of the principal displacement zone of the fault system. The three-dimensional architecture of the pull-apart basins is strongly controlled by the magnitude and type of motion along the principal displacement zone, and by the geometry of the underlying basement-fault systems. The identification of the deep crustal features within a fault zone and the analyses of the sedimentary settings associated with strike-slip motion are thus key elements to reconstruct the geometry and the kinematic development of the transcurrent system. Data gathered during the TESAC project off the Atlantic coast of the Tierra del Fuego, along Lago Fagnano - a major depression which hides a significant part of the MFS - and the central-eastern part of Isla Grande, have imaged the surface and sub-surface structure of the transform fault and its associated basins. The MFS is composed of distinct tectonic lineaments that are segments of the transform system and are represented by mostly near-vertical faults, with polarities that change along the strike of the fault. The sedimentary architecture of the asymmetric basins formed within the principal displacement zone, in which the thick end of the depositional wedge abuts the transform fault, suggest simultaneous strike-slip motion and transform-normal extension, a common feature found in other continental transtensional environments. The Tierra del Fuego is one of the few places on Earth which offers the opportunity to observe the surface and subsurface geological features related to a continental transform plate boundary, but it is one of the least known because its remoteness and the difficulties of access in most of its territory. The presence of large peat zones, widespread lagoons, forestry covers and the absence of paths, have always impeded the collection of geophysical and geological data on a regular basis along the strike of the transform segment.