Abstract One of the main characteristics of the Borborema Province in northeastern Brazil is the abundance of granitic domains. The Lagoa das Pedras plutonic-volcanic Complex record remnants of early to late Neoproterozoic primitive to highly evolved magmas. U-Pb SHRIMP determinations and whole-rock geochemistry on the granitic to granodioritic Riacho do Icó Stock, which is the largest plutonic body of this complex, were conducted. Zircon dating reveals that this body was intruded in the crust at 607 ± 3 Ma, whereas metamorphic overgrowths are coeval within uncertainty (600 ± 8 Ma). Geochemical characteristics of this stock suggest that it corresponds to Cordilleran-type magmas injected in the lithosphere above a subduction zone. Sr and Y contents in addition to MgO and SiO2 values are compatible with high-silica adakite-like magmas, interpreted as the result of slab melting in deep-seated regions. Based on the integration of this study and literature data, we suggest that the Riacho do Icó intrusion might be a dismembered part of a major continental magmatic arc described in the Central Subprovince of the Borborema Province, marking the onset of the accretionary stage of the Brasiliano orogeny.

Abstract The Vieirópolis pegmatite field is characterized by amazonite pegmatites inserted in the Borborema Province. The Serra Branca pegmatite is hosted by the Serra Branca granites, which intruded partially the Serra Negra granites, and stands out by its amazonite mineralization. To comprehend the crystallization conditions and the source of this pegmatite and associated Serra Branca and Serra Negra granites, petrographic, mineral chemistry, geochronological and whole-rock geochemical data were used. The Serra Branca pegmatite is Cs-, Rb-, Pb-, Nb-, and Ta-rich. The Serra Branca granites (563 ± 2 Ma) are metaluminous to weakly peraluminous, crystallized under high fO2 conditions, pressure of 2.68-2.80 kbar and temperatures ranging from 667-670°C, with many zircon grains showing inherited cores of Paleoproterozoic ages. The Serra Negra granites (594 ± 4 Ma) comprises metaluminous granites crystallized under high fO2 conditions, temperatures within 711-751°C, pressure varying from 4.72 to 5.42 kbar. Both granites resulted from distinct partial melting degrees of a source similar to the Caicó Complex orthogneisses. The Serra Branca pegmatite geochemical data suggests that it was originated by extreme fractionation of the Serra Branca granites magma. The Serra Branca amazonite pegmatite is the first pegmatite mineralogically and geochemically characterized as Nb-Y-F (NYF)-type from the gadolinite subtype in the Borborema Province.

Abstract Ferroan granites (585-530 Ma) in the Transversal subprovince of the Borborema Province (BP) comprise two groups: G1) slightly peraluminous to metaluminous, alkali-calcic rocks (Aroeiras Complex and Serra Branca - Coxixola dike swarms (SBCDS)); G2) metaluminous to slightly peraluminous, alkalic to alkali-calcic rocks (Queimadas and Prata intrusions). G1 are transitional from collision to transcurrence (ca. 585 Ma), or transcurrence to transtension (ca. 545 Ma). G2 represents the granitoids intruded during post-collisional crustal thinning (ca. 550 Ma), or coeval with deposition of intracratonic basins (ca. 530 Ma). The large-ion lithophile elements (LILE) and high field strength elements (HFSE) enriched geochemical signature of these granitoids are recognizable in gamma spectrometric maps of regional scale, highest values of K(%), eTh(ppm), and eU(ppm) contrast significantly with country rocks and magnesian granites. This study shows that gamma-ray spectrometric regional maps reflect the geochemical characteristics of the ferroan intrusions. Moreover, in the local maps for each intrusion, it is possible to identify internal heterogeneities in these plutons, which correlate to geological processes, geochemistry, and petrography. Diorites and gabbros show low to medium values of K (1-3%), eTh (5-20 ppm) and eU (0.2-2 ppm), contrasting with the high values of regions with a dominance of ferroan granitoids (K, 3-6%; eTh, 15-60 ppm; eU, 2-4 ppm).