SOBRE 0 COMPORTAMENTO ESPACIAL DO TRAPP BASÁLTICO DA BACIA DO PARANÁ

This paper deals with aspects of the great lava flows that occupy large areas of Couthern Brazil, Northern Uruguay and Argentina and a small part of Eastern Paraguay. Data obtained from oil drillings of Petrobras and the A.N.C.A,P., reveal great thicknesses of the basaltic rocks in the region of Parana basin. The isopach map of the trapp, designed with basis on these data, suggests a bulk of lavas of the order of at least 650.000 km 3 . The greatest thicknesses, almost reaching 1.800 m are observed in the zone of Presidente Epitacio to the south, partly coincident with the central region of the basin. The eletrical log of the Presidente Epitacio well, indicates the existence of 32 lava flows, with individual thicknesses averaging 50m. In the region of the Br-2 highway situated between the Pelotas and Cai rivers (Rio Grande do Sul), the behavor of structures such as joints, vesicles, "vulcanic" breccias, etc., has been observed. The features of these breccias induced us to consider them as aglomeratic lavas, ocurring at the top of some flows. It has been also verified, through the evaluation of properties as density, refraction index and percentage of glasses, that the lavas are quite heterogenious, opposingly to what is generally supposed. The mean refraction index values of 1,54 to 1,59 for the glasses of the "Lauro Muller - Sao Joaquim" section, seem to indicate a strongly basaltic composition, while in the "Tainhas - Faxinal" section, these values decrease to 1,51 - 1,52 , indicating a reasonably acid composition. There is also a general tendence of the lavas with high densities to occupy lower stratigrafic positions than those with smaller weight. In the "Rio Turvo" section, it can be distinguished a neat relation between density of the lavas and their glass content, i. e., to an increase of the glass content, corresponds a diminution of density values.