The Magallanes and Deseado fault zones: Major segments of the South American‐Scotia transform plate boundary in southernmost South America, Tierra del Fuego

Abstract

The 600‐km‐long Magallanes fault zone and the newly discovered 100‐km‐long Deseado fault zone represent large but little understood segments of the South American‐Scotia (SAM‐SCO) transform on the South American continent (∼50–56° S latitude). Kinematic analyses of fault populations near Mount Hope on Tierra del Fuego indicate that these fault zones have accommodated sinistral strike‐slip motion with a probable component of normal slip on vertical‐subvertical faults during Cenozoic time. Regional geological data and overprinting relationships between the strike‐slip/oblique‐slip faults and mid‐Cretaceous to Oligocene contractional structures suggest that sinistral motion in the Mount Hope segments of the two fault zones occurred significantly since ∼60 Ma and dominantly since ∼30 Ma with the most recent episode of activity occurring during the Quaternary. Results from mapping show 20–25 km of cumulative sinistral separation of a thrust contact across a well‐exposed segment of the Magallanes fault zone north and east of Mount Hope. Although the exact amount of displacement accommodated by this segment of the Magallanes fault zone remains uncertain, the 20–25 km of cumulative sinistral separation combined with an estimate of 3 km of vertical separation is consistent with small magnitudes of displacement of the order of tens of kilometers. This result apparently contrasts with predictions based on plate reconstructions that large amounts of strike‐slip displacement (>200 km) have been accommodated internally within southernmost South America since early Cenozoic time. A low magnitude of displacement along the Mount Hope segment of the Magallanes fault zone suggests that (1) strike‐slip motion has been partitioned across the continent since about 30 Ma and/or (2) the Mount Hope segment of the Magallanes fault zone represents a young part of the modern plate boundary that migrated to its present location during the last few million years.

Continental underthrusting and obduction during the Cretaceous closure of the Rocas Verdes rift basin, Cordillera Darwin, Patagonian Andes

“…[9] Beginning in the late Oligocene or early Neogene, convergence in the southernmost Andes declined and sinistral strike-slip faulting dominated [Cunningham, 1993;Klepeis, 1994b;Klepeis and Austin, 1997;Diraison et al, 2000;Ghiglione and Ramos, 2005;Lodolo et al, 2003;Gombosi et al, 2009]. This transition coincides with for-mation of the South American-Scotia transform fault boundary [Rossello, 2005].…”

Shallow architecture of Fuegian Andes lineaments based on Electrical Resistivity Tomography (ERT). Evidences of transverse extensional faulting in the central Beagle Channel area

“…A subsequent strike-slip deformation stage is widely recognized within the Tierra del Fuego Island and the southern archipelago, overprinting earlier contractional folds and faults (Betka et al, 2016;Cunningham, 1993;Klepeis and Austin, 1997;Lodolo et al, 2003;Menichetti et al, 2008;Torres Carbonell et al, 2008b), with reported displacements up to several kilometers (Klepeis, 1994;Rossello, 2005;Torres-Carbonell et al, 2008b). However, there is no agreement about the onset timing and the tectonic regime under which the transcurrent deformation took place.…”

“…The transcurrent regime is characterized by E-W to ESE-WNW left-lateral strike-slip faults arranged in several regional fault systems with strong morphostructural expressions such as the BCFZ, the Andorra valley (Menichetti et al, 2008) and the Magallanes-Fagnano Fault System (MFFS), which comprises the inland segment of the transform plate boundary between South American and Scotia Plates (Fig. 1) (Klepeis, 1994;Lodolo et al, 2003). It extends eastwards, into the offshore, along the North Scotia Ridge (Barker, 2001;Eagles, 2016).…”

Geometría del basamento y espesores sedimentarios del lago Fagnano (Tierra del Fuego).

“…These basins are known along the entire segment for more than 600 km from the Pacific Ocean through the Magallanes Strait, the Seno Almirantazgo, the LF, to the Atlantic off-shore (Fuenzalida, 1972;Dalziel, 1989;Lodolo et al, 2003;Tassone et al, 2011). LF occupies the central segment of the MFS for a length of more than 100 km with a E-W strike (Klepeis, 1994;Lodolo et al, 2002aLodolo et al, , 2003. The structures of the LF area have been affected by two tectonic phases: (I) the Late Cretaceous Andean compressional phase with a prevalent ductile deformation, and (II) the Oligocene-Quaternary strike-slip phase where the deformation is essentially brittle Esteban et al, 2009Esteban et al, , 2011.…”