Table of Contents
Journal of Geological Research
Volume 2013, Article ID 590835, 22 pages
http://dx.doi.org/10.1155/2013/590835
Research Article

Magmatism in the Asunción-Sapucai-Villarrica Graben (Eastern Paraguay) Revisited: Petrological, Geophysical, Geochemical, and Geodynamic Inferences

1Mathematics and Geosciences Department, Trieste University, Via Weiss 8, 34127 Trieste, Italy
2Geotrack International, 37 Melville Road, Brunswick West, Melbourne, VIC 3055, Australia
3Geosciences Institute, University of São Paulo, Cidade Universitária, Rua do Lago 562, 05508-900 São Paulo, SP, Brazil
4Astronomical and Geophysical Institute (IAG) of the São Paulo University, Rua do Matão 1226, 05508-090 São Paulo, SP, Brazil

Received 12 November 2012; Revised 25 March 2013; Accepted 8 April 2013

Academic Editor: David T. A. Symons

Copyright © 2013 Piero Comin-Chiaramonti et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The Asunción-Sapucai-Villarrica graben (ASV) in Eastern Paraguay at the westernmost part of the Paraná Basin was the site of intense magmatic activity in Mesozoic and Tertiary times. Geological, petrological, mineralogical, and geochemical results indicate that the following magmatic events are dominant in the area: (1) tholeiitic basalt and basaltic andesites, flows and sills of low- and high-titanium types; (2) K-alkaline magmatism, where two suites are distinguished, that is, basanite to phonolite and alkali basalt to trachyte and their intrusive analogues; (3) ankaratrite to phonolite with strong Na-alkaline affinity, where mantle xenoliths in ultramafic rocks are high- and low-potassium suites, respectively. The structural and geophysical data show extensional characteristics for ASV. On the whole, the geochemical features imply different mantle sources, consistently with Sr-Nd isotopes that are Rb-Nd enriched and depleted for the potassic and sodic rocks, respectively. Nd model ages suggest that some notional distinct “metasomatic events” may have occurred during Paleoproterozoic to Neoproterozoic times as precursor to the alkaline and tholeiitic magmas. It seems, therefore, that the genesis of the ASV magmatism is dominated by a lithospheric mantle, characterized by small-scale heterogeneity.