[en] Four groups of granitoids are present within the Cachoeirinha belt and in the adjacent migmatitic basement, between 37⁰ and 40⁰ W long. and 7⁰ and 8⁰15' S lat., States of Pernambuco and Paraiba: a) K₂O - enriched, very porphyritic; b) a calc-alkalic slightly porphyritic group; c) group with trondjemitic affinities; and d) peralkalic group. Petrology and oxygen isotope geochemistry for over 100 samples from these groups were studied. Almost all plutons for which 5 or more samples were analyzed, exhibit a total range of gamma ¹⁸O less than 2% o. A broad range of mean oxygen isotope composition is observed, varying from 6.93 to 12.79% o. There is a systematic regional trend in which the calc-alkalic granitoids (conceicao-type) found within the Cachoeirinha space are the most ¹⁸O - enriched rocks (10.6 to 12.9% o) while the lowest mean gamma ¹⁸O values (4.5 to 9.7% o) are found in the K₂O - enriched granitoids (Itaporanga-type). Intermediate gamma ¹⁸O values were recorded in the bodies with trondhjemitic affinities (8.9 to 9.8% o) which intruded metasediments of the Salgueiro Group and in the peralkalic granitoids of Catingueira (8.1 to 9.8% o) which intruded Cachoeirinha metamorphics. Among the potassic granitoids, mean gamma ¹⁸O increases from Bodoco to Itaporanga (from west to east). As a whole, the W.R. gamma ¹⁸O of these plutons correlate with the type of grade of metamorphism of the host rocks and, therefore, with the tectonic framework, increasing from those which intruded the gneiss-migmatites to those which intruded the low-grade metamorphics of the Cachoeirinha Group. The possible origin of each rock group is discussed in light of the oxygen isotope geochemistry. (Author)