GRANITOIDS MARKING THE END OF THE BRASILIANO (PAN - AFRICAN) OROGENY WITHIN THE CENTRAL TECTONIC DOMAIN OF THE BORBOREMA PROVINCE

Resumo

The studied syenogranite and granodiorite intrusions have a similar U-Pb zircon age (ca 570 Ma). They are intruded in the Central Tectonic Domain of the Borborema Province, forming an S-type belt in relation to the Patos and Pernambuco Lineaments. The studied granitoids are clinopyroxene biotite leuco-syenogranites of the Solidão Pluton; amphibole biotite sienogranites from the Queimadas Pluton; biotite granodiorite and amphibole biotite granodiorite, which occur as dikes cutting the Itapetim Complex and leuco-syenogranites from the Serra Branca Pluton. They show geochemical data transitional between shoshonitic and alkaline series. Deep troughs at Nb, Sr, P and Ti and high LILE/HFSE ratios characterize the spiderdiagram patterns. The ÎNd (0.6 Ga) values are extremely negative (- 11 to -16; except for the Itapetim dykes ~-3) and Nd model ages (T_DM) range from 2.0 Ga to 2.5 Ga (the Itapetim dykes ~1.4Ga). Biotites of the studied granitoids are Fe-rich with Fe/(Fe+Mg) ratios in the 0.62 to 0.84 range. Biotites from older granitoids (640 Ma -580 Ma) of the Pajeú - Paraíba Terrane, have Fe/(Fe+Mg) ratios < 0.60. The isotopic and geochemical data suggest that the studied granitoids correspond to a trans-alkaline, ferro-potassic plutonism, originated by partial melting of Paleoproterozoic and Mesoproterozoic crusts, emplaced during the final stage of the Brasiliano Orogeny in the Central Tectonic Domain of the Borborema Province.