Cenozoic geodynamic evolution of Tierra del Fuego (Northwestern Scotia Arc) from fracture population analysis

MAESTRO, ADOLFO; RUANO, PATRICIA; TORRES CARBONELL, PABLO; BOHOYO, FERNANDO; GALINDO-ZALDÍVAR, JESÚS; PEDRERA, ANTONIO; RUIZ-CONSTÁN, ANA; GONZÁLEZ-CASTILLO, LOURDES; IBARRA, P.; LÓPEZ-MARTÍNEZ, J.

Kuala Lumpur

Conferencia; XXXIV SCAR: Biennial Meetigs & Open Science Conference 2016. Antarctica in the Global Earth System: From the Poles to the Tropics.; 2016

SCAR - Ministry of Science, Technology and Innovation, Malasia

Tierra del Fuego represents the northwestern branch of the Scotia Arc and its largest emerged sector. Itcomprises the southernmost segment of the Andean Cordillera that forms a regional orogenic reentrant arcwith a NW-SE to E-W trend commonly referred to as the Patagonian orocline. The main objectives of thisresearch are: (i) Characterizing the different Cenozoic palaeostress fields in Tierra del Fuego region and (ii)Establishing the relationship between the evolution of major tectonic structures and the orientation of thestress fields. To do that, 1496 faults, joints, tension gashes and clastic dikes were measured at 87 siteslocated in Upper Jurassic to Quaternary rocks. A total of 124 palaeostress tensors were obtained using theRight Dihedra, the y-R diagram, the Etchecopar´s and the Search Grid Inversion Palaeostress determinationmethods. Although the tectonic analysis was primarily based on palaeostress reconstructions using fault-slipdata, the orientation of tensional joints, gashes and clastic dikes have also been used to establish maximumand minimum horizontal stress trends.From the stress axes directions, a dominant NE-SW ζ1 (maximum compression) direction as well as NW-SEand N-S secondary ζ1 stress directions are observed. The ζ3 (minimum compression) orientation shows twomain modes trending ENE-WSW and NW-SE, and three secondary ζ3 stress directions (NE-SW, E-W andNNW-SSE). The R relationship of the NE-SW ζ1 mainly indicates an axial compression to wrench regime.The NW-SE and N-S horizontal main stress directions have an R relationship ranging from axial compressionto tensional regimeObtained stress evolution is consistent with the regional NE-SW compressive stress field active in the areasince Lower Cretaceous.The NE-SW subduction of the Phoenix Plate under Antarctica and South America plates at the end of theLower Cretaceous is related with a major episode of crustal shortening, which led a widespread folding afaulting to the Tierra de Fuego basement with a structural trend N-S to NW-SE. During the Upper Cretaceousstarted the closure of the Rocas Verdes back arc basin, developed in the Middle-Upper Jurassic inrelationship with the Gondwana fragmentation, linked to the progression of the contractional deformation withNE-SW direction. This closure could have produced a maximum regional counterclockwise rotation of 30°that developed the Patagonian orocline, and arranged the NW-SE structures to an E-W direction. The finalstructural curvature may have been acquired due to the interaction of the orogenic wedge with the Río Chicopromontory during Upper Cretaceous-Oligocene. The promontory indentation caused a variation in the trendof the compressive stress axis along the Tierra del Fuego, showing NE-SW direction in the western part andN-S to NW-SE in the eastern sector. Finally, since late Miocene, the activity of the North Scotia Ridgeprovokes strike-slip faulting in Tierra del Fuego that deflects the NE-SW stress trajectories changing to E-Wdirection near of the major Magallanes-Fagnano Fault System.