Magnetotelluric characterization through the Ambargasta-Sumampa Range: The connection between the northern and southern trace of the Río de La Plata Craton e Pampean Terrane tectonic boundary

GISEL PERI; HERNAN BARCELONA; C. POMPOSIELLO; A. FAVETTO

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2015 vol. 59 p. 1 - 12

0895-9811

The South American Platform was part of the Western Gondwana, a collage of plates of different agesassembled in late Neoproterozoic to Cambrian times. The Transbrasiliano Lineament, a continental shearbelt that transversely intersects this platform from NE to SW, has its southern expression in the tectonicboundary between the Río de La Plata Craton and the Pampean Terrane. Magnetotelluric long-perioddata in a WeE profile (29300 S) that crosses the Ambargasta-Sumampa Range and the Chaco-Pampean Plain were obtained to connect information of this mostly inferred tectonic boundary. A 2-Dinversion model shows the Chacoparanense basin, Río Dulce lineament, Ambargasta-Sumampa Rangeand Salina de Ambargasta in the upper crust. At mid-to-lower crust and 40 km to the east of theAmbargasta-Sumampa Range, a discontinuity (500e2000 U m) of 20-km-wide separates two highlyresistive blocks, the Río de La Plata Craton (6000e20,000 U m) in the east, and the Pampean Terrane(5000e20,000 U m) in the west. This discontinuity represents the tectonic boundary between bothcratons and could be explained by the presence of graphite. The geometry of the Pampean Terranesuggests an east-dipping paleo-subduction. Our results are consistent with gravimetric and seismicitydata of the study area. A more conductive feature beneath the range and the tectonic boundary wasassociated with the NEeSW dextral transpressive system evidenced by the mylonitic belts exposed in theEastern Pampean Ranges. This belt represents a conjugate of the mega-shear Transbrasiliano Lineamentand could be explained by fluiderock interaction by shearing during hundreds of years. The easternborder of the Ambargasta-Sumampa Range extends the trace of the Transbrasiliano Lineament.The electrical Moho depth (40 km to the west and 35 km to the east) was identified by a high electricalcontrast between the crust and upper mantle. The upper mantle shows a resistive structure beneath theRío de La Plata Craton that could have been originated by stationary delamination by the presence ofhydrated lithosphere.