Multiple stages of migmatite generation during the Archean to Proterozoic crustal evolution in the Borborema Province, Northeast Brazil

Abstract

Multiple partial melting events are documented for Archean to Neoproterozoic migmatites in the Campo Grande granitoid terrain of the Borborema Province of NE Brazil. The migmatites bear evidence of a complex history with different melt generations evidenced by 2.9 Ga tonalite, 2.65 Ga granodiorite, 1.95 Ga in-situ granite leucosomes, and c. 570 Ma injected alkali-feldspar granite leucosomes. Pb-Hf-Nd isotopes reveal c. 2.9 Ga juvenile and 3.25 Ga reworked sources for the 2.9 Ga tonalite and 2.65 Ga granodiorite residue. The 1.95 Ga Paleoproterozoic in-situ granite leucosomes show strong negative to weakly positive εHf(t) and εNd(t) values, with TDM(Hf and Nd) model ages between 2.4 and 2.9 Ga. In contrast, the c. 570 Ma Neoproterozoic injected alkali-feldspar granite leucosomes have more negative εHf (t) and εNd(t) values, with younger TDM(Hf and Nd) of 2.1–2.3 Ga. However, all migmatite components show a progressive increase of LILE and HREE elements from 2.9 Ga tonalite to c. 570 Ma alkaline granite phases, which indicates differentiation of continental crust in this region. The partial melting processes could have been the result of magmatic heating and release of H2O-rich fluids due to 1.95 Ga and c. 570 Ma post-collisional magmatism. Thus, Archean tonalitic and granodioritic protoliths went through multiple Proterozoic orthoderived leucosome generations within the continental crust, suggesting that crustal reworking by anatexis was a crucial factor in the complex evolution of this migmatite terrain.