Geophysical data acquisition - OGS

Structure and Cenozoic evolution of the South America –
Scotia plate boundary in the Tierra del Fuego region
E. LODOLO
R. GELETTI
Onshore field geological and geophysical studies, and a multichannel seismic
survey have been conducted in the last two years in the Tierra del Fuego region, in
the frame of an Argentinean-Italian scientific research. The main aim of this
project was to analyse the regional geological setting of the Island and reconstruct
the Cenozoic geodynamic evolution of an important segment of the South
America-Scotia plate boundary, called Magallanes-Fagnano fault system. This is a
mainly wrench lineament which cuts across the Island and runs from the Pacific
entrance of the Magallanes Strait to the Atlantic coast of the Island. The Lago
Fagnano, located in the central part of the Tierra del Fuego, is an E-W-trending
major depression which hides part of the fault, as revealed by the bathymetric map,
which shows the presence of significant and steep scarps in correspondence of the
onshore prosecution of the lineament. In cross-section, this tectonic lineament is
represented by sub-vertical faults and associated asymmetric basins, generated by
simultaneous strike-slip motion and transform-normal extension, as imaged by
the seismic profiles acquired off the Atlantic coast of the Island and in the central
and western Magallanes Strait.
Data analyses support the interpretation that the Magallanes-Fagnano fault system
is remarkably transtensive in nature, and is structurally and temporally
superposed on the older tectonic framework of the Tierra del Fuego (i.e., the
contractional system of the Magallanes fold and thrust belt), even if the
displacement history of this fault system is unclear. The near parallelism among
the younger and older lineaments suggests that the development of the
transtensional structures may have reactivated pre-existing weakened zones
formed by the Cretaceous-Tertiary shortening.
Mapping the BSR on the South Shetland Margin
(Antarctica) and assessing gas hydrate and free gas
quantities
E. LODOLO
A. CAMERLENGHI
G. MADRUSSANI
G. ROSSI
U. TINIVELLA
Bottom Simulating Reflectors (BSRs) along the South Shetland continental
margin have been first identified by OGS researchers on two multichannel seismic
profiles acquired by the R/V OGS-Explora (1990 Antarctic Campaign). A dedicated
survey was conducted on 1997 to purposely map the extent of the BSR on this
margin, and study the relationships between geological structure and gas hydrate
and free gas distribution. Processing and interpretation of the collected grid of
high-resolution multichannel seismic reflection profiles have been completed
(about 700 km of data), and have allowed us to map the lateral extent of the BSRs.
The South Shetland continental margin, an accretionary wedge located off the
northern tip of the Antarctic Peninsula, consists of two distinct and superimposed
tectonic regimes: an older regime is related to Mesozoic - Middle Cenozoic
subduction-related tectonism; a younger one is associated with a mainly
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