Adejardo Francisco da Silva Filho

Nd and Sr-Isotopic and U-Pb Geochronologic Constraints for Evolution of the Shoshonitic Brasiliano Bom Jardim and Toritama Complexes: Evidence for a Transamazonian Enriched Mantle Under Borborema Tectonic Province, Brazil

The Bom Jardim and Toritama complexes form elongated bodies between the Pernambuco-Alagoas massif and Pajeu-Paraiba fold belt and comprise multiphase intrusions of monzonitic and syenitic compositions. Low-angle foliation recorded in both complexes, indicated by alignment of euhedral minerals, runs parallel to the main thrust faults within the region. This suggests that emplacement of the complexes could be related to the thrust faults. The whole-rock geochemistry of major and trace elements, and the associated mineral chemistry, have established a shoshonitic affinity for these complexes. The mineral chemistry of the essential minerals within both complexes, the presence of magnetite, and the constant Fe/Fe + Mg ratios in biotites and amphiboles with increasing differentiation indicate trends compatible with a fractionating magma under high f(O2) conditions. The general overlap and similarities in mineral chemistry between the mafic minor facies and the less-evolved members of the major facies indicate t...

Intralithospheric differentiation and crustal growth: Evidence from the Borborema province, northeastern Brazil

Thousands of cubic kilometers of high-K calc-alkalic magmas intruded the Borborema Province (northeastern Brazil) during the Neoproterozoic Brasiliano orogeny. They make up large batholiths in which mantle-derived mafic to intermediate rocks coexist with a larger amount of granitoids. The relatively low silica contents (61‐70 wt% SiO 2 ) and moderate to high compatible element concentrations (0.3‐3.5 wt% MgO, 1.5‐3.8 wt% CaO, as much as 150 ppm of Cr) of the granitoids indicate that they contain an appreciable mantle component. The similar trace element geochemical (high contents of incompatible trace elements) and isotopic (strongly negative eNd values) signatures of mafic and felsic rocks combined with geochemical modeling suggest that (1) the mafic and felsic rocks are genetically linked, (2) the granitic magmas were produced by 20%‐30% partial melting from a source having geochemical characteristics similar to the mafic rocks, and (3) mingling and mixing of felsic magmas with subsequent batches of mafic magmas yielded the silica-poor granitoids. Isotopic data preclude involvement of the asthenosphere in the genesis of the mafic melts and instead indicate their derivation from an old, enriched lithospheric mantle. Therefore, addition of mantle material to the crust occurred through internal lithospheric differentiation, in contrast with conventional crustal-growth models.

A-Type Post-Collisional Granites in the Borborema Province - NE Brazil: The Queimadas Pluton

Abstract The Queimadas Pluton constitutes an E-W elongated tabular intrusion, exposed over an area of 50 km 2 . It is intruded in Paleoproterozoic gneiss-migmatite of the Alto Pajeu Terrane in the Central Tectonic Domain of the Borborema Province, and has a zircon U-Pb age of 570±20 Ma. It is cut by later shear zones with NNE direction, which provoked necking and disruption in the body. A suite of biotite±amphibole monzogranites, associated with quartz diorite and later leucogranite and diabase, dominates in these alkaline granites that are metaluminous to slightly peraluminous and show high FeOt/(FeOt + MgO) and K 2 O/Na 2 O ratios. Their REE patterns are moderately fractionated, with (Ce/Yb) N ratios of 10-16 and significant negative Eu anomalies (Eu* = 0.40-0.67). Geochemical and Nd isotopic data indicate that the Queimadas Pluton magma originated by partial melting of a crustal fertile granodioritic rocks. The studied granites crystallized under relatively low f O 2 and are A-type post-collisional granitoids.

Long-lived Neoproterozoic high-K magmatism in the Pernambuco–Alagoas Domain, Borborema Province, northeast Brazil

The Pernambuco–Alagoas (PE–AL) Domain contains major granitic batholiths typified by a wide range of TDM model ages (Archaean to Neoproterozoic), reflecting the important role of quartzofeldspathic plutons attending the Brasiliano (Pan-African) Orogeny. U/Pb zircon data for eight syn- to post-collision to syn-transcurrent granitic intrusions of the PE–AL Domain allow the studied plutons to be divided into two groups: (1) granitoids with crystallization ages older than 600 Ma (Água Branca, Serra do Catú, Serra da Caiçara, and Mata Grande plutons) and (2) granitoids with ages of ca. 590 Ma (Correntes, Águas Belas, Viçosa, and Cachoeirinha plutons). The intrusions of group 1, except for the Mata Grande Pluton, all show Nd TDM model ages ranging from 1.5 to 1.2 Ga, whereas the granitoids from group 2 and the Mata Grande Pluton have Nd TDM model ages ranging from 2.2 to 1.7 Ga. The studied granitoids are in part high-K, calc-alkaline, shoshonitic, and in part transitional high-K calc-alkaline to alkaline in terms of their bulk chemistry. Volcanic arc signatures associated with the Palaeoproterozoic TDM model ages are interpreted as inherited from the source rocks. The oldest ages and higher Nd TDM model ages recorded in the granitoids intruded in the southwestern part of the PE–AL Domain suggest that these intrusions are associated with slab-tearing during convergence between the PE–AL and Sergipano domains. The investigated plutons are coeval with high-K granitoids intruded within the Transversal Zone Domain of Borborema Province and calc-alkaline granitoids of the Sergipano Domain. This suggests that these geologic realms belonged to the same crustal block during the Brasiliano Orogeny. However, such large volumes of high-K granitoids with crystallization ages older than 600 Ma are not recorded in the Sergipano and Transversal Zone domains, suggesting differences in the crustal evolution of these three areas.