The Asunci ́on-Sapucai-Villarrica graben (ASV) in Eastern Paraguay at the westernmost part of the Paran ́a 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.Thestructural 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
tholeiiticmagmas. It seems, therefore, that the genesis of the ASVmagmatism is dominated by a lithosphericmantle, characterized
by small-scale heterogeneity.
1. Introduction
Vel ́azquez et al. [1] presented a structural analysis of the
central segment of the “Asunci ́on Rift,” mainly based on the
previous papers related to the Eastern Paraguay magmatism
in general, and to the Asunci ́on-Sapucai-Villarrica graben
(ASV) in particular, and also based on extensive field data
collected earlier on the dyke swarms cropping out in the area.
However, some aspects as, for example, the close association
in space of potassic and sodic alkaline rock-types with
tholeiitic dykes and flows (both of high- and low-Ti types; cf.
[2]), have not been discussed in detail by the above authors.
This paper focuses on general aspects of the magmatism
from the
