Mississippian lamprophyre dikes in western Sierras Pampeanas, Argentina: Evidence of transtensional tectonics along the SW margin of Gondwana

MARTINA, FEDERICO; CANELO, HORACIO N.; DÁVILA, FEDERICO M.; DE HOLLANDA, MARÍA HELENA M.; TEIXEIRA, WILSON

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2018 vol. 83 p. 68 - 80

0895-9811

In the Famatina range, Sierras Pampeanas of Argentina (SW Gondwana), subvertical calc-alkaline lamprophyricdike swarms crop out through >300 km. The dikes cut Ordovician units with a prominent NW-SEtrending and are covered by continental sedimentary successions of Pennsylvanian to Permian age. Thedikes show a strong structural control associated with Riedel fault systems. Detailed field analysis suggesteda ~N-S opening direction oblique to the attitude of dike walls and a left-lateral transtensional tectonicsduring the emplacement. 40Ar/39Ar geochronology of a lamprophyric sample defined a crystallizationage (plateau; whole rock) of 357.1 ± 7.1 Ma (MSWD¼ 2.3). Coetaneous ductile zones with dominant strikeslipmotion, documented along western Argentina for >600 km, suggest a regional event in SWGondwanaduring the Mississippian. We propose that this deformation was the result of the counterclockwise fastrotation of Gondwana between 365 and 345 Ma, when the Famatina range and western Argentina occupieda sub-polar position. A transform margin along SW Gondwana better explains our (and others) data ratherthan a subduction margin. This scenario is also consistent with the occurrence of A-type granites andnormal-fault basins within the foreland as well as bimodal volcanics.