Abstract The Fellingsbro granite sensu stricto is a porphyritic coarse-grained rock characterized by red angular microcline megacrysts. A total of 52 samples of the Fellingsbro granite and the Lisjo granite (of the same type and situated 20 km to the northeast) have been analysed for major elements and Ba, Rb, Sr, Cu, Zn, Pb, Ga, Y, Zr, Nb, Mo, Th and U. Ten samples were analysed for REE, Ta, Hf, Cs and Sc. Both intrusions belong to a belt of ca. 1.78 Ga old granites which coincides with a major negative gravity anomaly, the so-called Central Swedish Gravity Low, We have carried out gravity measurements and obtained a fairly dense regional gravity network from the Fellingsbro area to Vasteras. In addition, an approx. 60 km long profile with gravity stations ca. 200 m apart was measured across the Lisjo granite. The porphyritic Fellingsbro and Lisjo granites were generated in a tensional environment. They rose from a huge granite ridge through structurally controlled root zones, flowed out and formed mushr...