Abstract
Abstract. There has been little research on volcanological aspects of Paraná continental flood basalts (PCFBs), and all investigations have mainly been concentrated on the internal portions of the lava flows. Thus, this study describes for the first time morphological aspects of lava flows and structural characteristics caused by lava–sediment interaction in the northwestern PCFB province (NW-PCFB). Early Cretaceous (134 to 132 Ma) tholeiitic rocks of the PCFB were emplaced on a large intracratonic Paleozoic sedimentary basin (Paraná Basin), mainly covering dry eolian sandstones (Botucatu Formation). As this sedimentary unit is overlain by the basic lava flows of the PCFB, the interaction of lavas and unconsolidated sediments resulted in the generation of fluidal peperites. This aspect is significant because it shows that restricted wet environments should have existed in the Botucatu desert. The peperite zones of the NW-PCFB are associated with compound pahoehoe-type (P-type) flows and are always related to the first volcanic pulses. These flows have dispersed vesicles and sand-filled cracks in their base and top borders, as well as the presence of interlayered sandstones with irregular contacts and varied thicknesses. It is remarkable that, to the best of current knowledge, only in this area of the whole PCFB did the volcanic activity start with low-Ti basalt flows of Ribeira type (TiO2 < 2.3 wt%), which are scarce in the province.
Highlights
Continental flood basalts (CFBs) are the result of brief igneous events that may last only a few million years or less, producing vast volumes of lavas and intrusive rocks (Coffin and Eldholm, 1994)
The main goal of this study is to describe the morphological aspects of lava flows and the structural characteristics caused by lava–sediment interaction in the northwestern Paraná continental flood basalts (PCFBs) (NW-PCFB; Fig. 1), as well as to discuss the mechanisms involved during the extrusion processes
Thirty-six samples were collected in the northwestern PCFB province (NW-PCFB) and analyzed for major, minor, and some trace elements (Cr, Ni, Sr, Y, Zr, and Nb) by X-ray florescence (XRF), at the Universidade Estadual Paulista (UNESP, Brazil)
Summary
Continental flood basalts (CFBs) are the result of brief igneous events that may last only a few million years or less, producing vast volumes of lavas and intrusive rocks (Coffin and Eldholm, 1994). As emphasized by Self et al (1997) and Skilling et al (2002), the physical volcanology of CFBs has received relatively little attention, since many previous studies have tried to understand their petrological, geophysical, geodynamical, and geochemical features, identifying possible mantle sources, crustal or mantle contaminants, and lowpressure magma evolution of the basalts generated in these magmatic processes. One of the first provinces where this kind of investigation was accomplished is the Columbia River basalts, whose flows are mainly compound pahoehoe (Riedel and Tolan, 1992), presenting peperites as a result of the interaction of lava flows with unconsolidated sedimentary deposits (Riedel, 1998). Regarding the Ferrar volcanic province, Antarctica, the peperites formed by mingling of basalt flows
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