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The northwestern portion of the Gondwanian Paraná Basin, Brazil, lies on a gneissic-granitic terrane with characteristics of its own that discriminate it from the rest of the basement rocks. Such special geologic and geophysical characteristics led us to indicate the existence of a special continental lithosphere segment, the "Paranapanema Block". A few direct geologic data obtained from deep drill holes show that it has a pre-Brasiliano origin. From the geotectonic point of view, this continental lithospheric segment first acted as an upper plate during subduction processes and subsequently as a backland, during the interaction with neighboring plates. Zones of plate interaction mark the external limits of this portion of the basin (west, north-northeast and east), with the generation of continental magmatic arcs and post-collisional structures.
The gravimetric configuration of the basement for the Paraná Basin corroborates the mentioned geological observations. The marked gradients define the boundary of such nucleus, and the distribution of extensional stresses, parallel to the western gradient, delineates a system of possibly reactivated faults that may have acted in the transport of the CFB magmas, the Serra Geral Formation. The main stresses are parallel to the South American coast, site of continental rupture for that latitude and east to that lithosphere segment. The presence of the block and the location of its northern portion were also confirmed by a MT survey.
The anomalous seismic velocities recordered in the northern portion of the lithosphere underlying the basin were interpreted as a "fossil plume", and small differences in velocity were associated with the presence of a cratonic block under the basin.
Regarding the CFB geochemistry and Sr and Pb isotopy, at least two major sources exist that geographically divide the area in a northern (associated with the Paranapanema Block) and a southern segment. The lithospheric nature of the magma sources is already accepted by many authors. Some of the recent works associate the CFB composition with "delamination" processes in the lower crust. In this context, the recent studies point to the existence of two lithospheric blocks, one of which is the Paranapanema.
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