Paleostress fields in Tierra del Fuego and their relationship with the scotia arc based on brittle mesostructure population analysis

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

Goa

Simposio; XII International Symposium on Antarctic Earth Sciences ISAES 2015; 2015

Scientific Comittee on Antarctic Research (SCAR)

Tierra del Fuego represents the largest emerged part at the northwestern end of the Scotia Arc and isconsidered the continuity of the Antarctic Peninsula. It also comprises the southernmost segment of theAndean Cordillera known as Fuegian Andes with a very complex tectonic history. Its recent history islinked to the Scotia Arc evolution, which promoted the development of geological features that aresignificantly different from the rest of the southern Andes.The main objectives of this research were: (i) characterize the late Jurassic to Quaternary tectonicpalaeostress fields in the Fuegian Andes region and (ii) to establish the relationship between theevolution of major tectonic structures and the orientation of the stress fields.To contribute to the knowledge of the tectonic evolution of the Fuegian Andes region, 1523 brittlemesostructures (1263 faults, 129 joints, 67 tension gashes and 64 clastic dikes) were measured at 86sites in Late Jurassic to Quaternary Metamorphic, igneous and sedimentary rocks. A total of 125 palaeostresstenSørs were obtained. Fault data were analyzed using the Right Dihedra, y-R diagram,Etchecopar's and Search Grid Inversion Palaeo-stress determination methods. Although the tectonicanalysis was primarily based on palaeo-stress reconstructions using fault-slip data, the orientations oftensional joints and gashes and clastic dikes have also been used to establish maximum and minimumhorizontal stress trends, although no quantitative estimation of stress ratios can be made.The whole faults are represented by 619 normal faults, 336 reverse faults and 308 strike-slip faults. Allthem show dips between 10° and vertical. Faults offset range between centimetres and a few metres. Thepopulation of normal faults presents a main N-S direction and two relative maxima striking ENE-WSWand ESE-WNW. The reverse faults show NNW-SSE and EW directions meanwhile the strike-slip faultshave preferentially N-S, NE-SW and NW-SE directions. Joints present a main NE-SW direction and threerelative maxima striking ESE-WNW, NWSE and N-S. Tension gashes data show N-S to NNE-SSW maindirections and several relative maxima striking NE-SW and NW-SE. Finally, clastic dikes show NNE-SSWto NE-SW directions. From the stress axes directions, a dominant NESW horizontal (maximumcompression) direction and NW-SE and N-S secondary horizontal stress directions are observed. The(minimum compression) orientation shows two main modes trending ENE-WSW and NW-SE, and threesecondary horizontal stress directions (NE-SW, E-W and NNW-SSE). The obtained (horizontal maximumcompression) orientation have a main mode trending NE-SW and two secondary modes with NW-SE andN-S directions. The R relationship of the NE-SW stress direction mode mainly indicates an axialcompression to wrench regime. The NW-SE and N-S horizontal main stress directions have an Rrelationship ranging from axial compression to tensional regime.These stress tensors are consistent with, and characterize: i) a N directed contraction that developedduring the late Cretaceous-early Paleogene oroclinal bending of the southernmost South America-Antarctic Peninsula continental bridge, and further movement of the Fuegian backstop toward SouthAmerica until the Miocene; and ii) the major strikeslip faulting in Tierra del Fuego, consistent withevolution of the North Scotia Ridge since ~10 Ma.