The Magallanes-Fagnano continental transform system (Tierra del Fuego) and its analogies with other strike-slip environments.

LODOLO, E.; TASSONE, A.; MENICHETTI, M.

Firenze, Italy

Congreso; 31 International Geological Congress.; 2004

IAG

South America-Scotia plate boundary in the Tierra del Fuego region. It runs from the Atlantic offshore to the westernmost arm of the Magallanes Strait, and traverses broadly E-W the entire Isla Grande, the main island of Tierra del Fuego. A significant part of the fault trace is hidden by the Lago Fagnano, a 105-km-long, mostly asymmetric pull-apart basin developed within the principal displacement zone of the fault system. Geological and geophysical data acquired in the last four years along most of the length of the fault have imaged with unprecedented detail the surface and sub-surface structure of the transform system. The Magallanes-Fagnano fault system is composed of distinct tectonic lineaments arranged in an en-echelon geometry and is represented by mostly near-vertical faults. In the Atlantic sector, the fault system seems to be composed by a single master fault, along which a highly asymmetric basin has formed. At around 63°W, the fault terminates by splaying into secondary normal faults. In the central-eastern part of Isla Grande, the fault segments have been principally identified from analyses of remote-sensing images. These segments are located within river valleys and are generally associated with localized gravity minima. Restraining bends and overlapping step-over geometry characterize the central part of the Magallanes Strait. In the Pacific entrance of the Magallanes Strait, asymmetric sedimentary basins have also developed. Surprising morphological, structural and tectonic analogies have been found in other continental transform systems. In eastern Guatemala, the Polochic fault marks a significant part of the North America-Caribbean plate boundary. Among the common characteristics of these systems, we may consider their gently curved trend, the presence of a subduction trench in their westernmost termination, the formation of large and elongated lakes within the principal displacement zone of the faults, the highly asymmetric configuration of their sedimentary fill. This sedimentary architecture, suggests simultaneous strike-slip motion and transform-normal extension. Those analogies may suggest a common tectonic mechanism responsible for the development of those transform systems, and possibly for the entire regions of the Caribbean and Scotia Arcs, whose morphological and geological similitude's have been largely recognized.