Paleoarchean to Neoproterozoic crust formation and migmatization events in the Borborema Province, NE Brazil: Implications for the growth and reworking of the continental crust

Abstract

The Patos Shear System (PSS) is a 20–40 km wide domain of anastomosing shear zones intercalated with non-mylonitic segments at the core of the Borborema Province, a transpressive Neoproterozoic orogen in NE Brazil, part of the reworked São Francisco Craton. We provide new U-Pb, Lu-Hf and Sm-Nd analyses for non-mylonitic basement migmatitic orthogneisses. Four magmatic events (∼3.40, 3.26, 2.68–2.64 and 2.18 Ga), as well as three metamorphic/migmatization ones (∼3.0, 2.1–2.0 Ga and 570–575 Ma) were evidenced. Metamorphism and leucosome injection at ∼570–575 Ma attest the PSS was subjected to high heat from medium- to high-temperature dextral shearing. A distinct Paleoproterozoic (∼2.1–2.0 Ga) migmatization event is probably related to the amalgamation of Neo-Paleoarchean blocks and an older ∼3.0 Ga metamorphic event may represent crustal thickening induced by the collision between small Paleoarchean landmasses. Paleoarchean magmatic protoliths obtained here were emplaced concomitant with TTGs and high-K rocks regionally, and our Hf data from these rocks, after filtering for isotopic disequilibrium during anatexis, combined with a large compilation, point to an apparent mixing of magma derived from a CHUR-like reservoir with older crust, better reconciled, although not conclusively, with a stagnant-lid scenario dominated by plume activity. Hf data from 2.68 to 2.64 Ga old migmatites plot along a conspicuous Meso-Neoproterozoic “reworking array” and our preferred model is that magmatism between 2.9 and 2.6 Ga took place in an accretionary/collisional continental setting, following renewed juvenile additions between ∼3.2 and 2.9 Ga. At last, the crystallization age of ∼2.18 Ga of an orthogneiss is related to another Wilson Cycle. Our data point to reworking of Archean lithologies during the Paleoproterozoic, as evidenced by inherited Archean zircon grains, but ƐHf and ƐNd close to CHUR suggest involvement of more juvenile material as well, consistent with regional data, and the preferred scenario is that of subduction followed by collision.