Geology
The geology of the archipelago is characterized by the effects of the Andean orogeny and the repeated Pleistocene glaciations. The geology of the island can be divided into large east-west oriented units. The southwestern islands of the archipelago, including Cape Horn, are part of the Patagonian Batholith, while Cordillera Darwin and the area around Beagle Channel forms the principal codillera hosting the highest mountains. The Magallanes fold and thrust belt extends north of Almirantazgo Fjord and Fagnano Lake, and north of this lies the Magallanes foreland; an old sedimentary basin that hosts hydrocarbon reserves. Orthogneiss dated at 525 million years of age is known to underlie some of the oil wells in northern Tierra del Fuego.
The Magallanes-Fagnano Fault, a dextral strike slip fault crosses the southern part of the main island from west to east. It is an active seismic fault, located in inside and parallel to the Fuegian fold and thrust belt marks the boundary between a southern belt of Paleozoic meta sediments and northern Mesozoic belts sedimentary sequences. The Fagnano Lake occupies an glacier-carved depression in a pull-apart basin developed along the Magallanes-Fagnano Fault zone.
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