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.
Highlights
Velazquez et al [1] presented a structural analysis of the central segment of the “Asuncion Rift,” mainly based on the previous papers related to the Eastern Paraguay magmatism in general, and to the Asuncion-Sapucai-Villarrica graben (ASV) in particular, and based on extensive field data collected earlier on the dyke swarms cropping out in the area
This paper focuses on general aspects of the magmatism from the western margin of the Parana-Angola-Etendeka system (PAE), where tholeiitic flows and dykes
Geological and geophysical results show that the MesozoicTertiary block-faulting tectonics in Eastern Paraguay is responsible for NW-trending grabens (ASV and Amambay), fault systems, and fault-controlled basins, for example, Jejui-Aguaray-Guazu, Asuncion-Encarnacion, San Pedro
Summary
Velazquez et al [1] presented a structural analysis of the central segment of the “Asuncion Rift,” mainly based on the previous papers related to the Eastern Paraguay magmatism in general, and to the Asuncion-Sapucai-Villarrica graben (ASV) in particular, and based on extensive field data collected earlier on the dyke swarms cropping out in the area. 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 western margin of the Parana-Angola-Etendeka system (PAE), where tholeiitic flows and dykes (Early Cretaceous, both of high-Ti and low-Ti types; cf Figure 1(a) and [3]) are associated in time and space with a wide variety of alkaline rock-types (both potassic and sodic) and carbonatites. The investigated alkaline and tholeiitic rocks from Eastern Paraguay span in age mainly from Early Cretaceous to Paleogene times They are germane to the magmatic and tectonic evolution of the PAE and of the Atlantic Ocean (cf Figure 1(b) and [4, 5]). (ASV) graben; (3) petrography and petrochemistry of the magmatic rock-types (and the associated mantle xenoliths) from ASV; (4) the most important geochemical and Sr-Nd isotopic features of the magmatism; (5) the petrogenesis and geodynamic implications
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