The Neoproterozoic Sergipano orogenic belt, NE Brazil: A complete plate tectonic cycle in western Gondwana

Abstract

The Neoproterozoic Sergipano Belt formed by the collision of the Pernambuco-Alagoas Block in the north with the São Francisco Craton in the south, but the timing, duration and mechanics of this amalgamation are poorly understood. The belt is divided into the Canindé, Poço Redondo-Marancó, Macururé, Vaza Barris, and Estância lithostratigraphic domains; the first three are composed of plutonic, volcanic and sedimentary rocks and the last three of sedimentary rocks. Our new field, structural, and geochemical data, and Sm–Nd, Ar–Ar and U–Pb geochronology provide robust constraints for the following evolution. A Mesoproterozoic (∼980–960 Ma) continental arc (Poço Redondo tonalitic gneisses) developed on the margin of the Palaeoproterozoic Pernambuco-Alagoas Block. Extension of this continental block gave rise to (i) A-type crustal granites and associated sedimentary rocks on the stretched, rifted margin of the Poço Redondo-Marancó Domain, (ii) the Canindé rift sequence between the Pernambuco-Alagoas Block and the Poço Redondo/Marancó domain, (iii) a passive margin on the southern boundary of the Pernambuco-Alagoas Block on which sediments were deposited after 900 Ma, (iv) and a second passive margin on the São Francisco Craton. In the Canindé Domain, rifting continued until ca. 640 Ma and led to emplacement of a bimodal association of A-type granite (715 Ma) and continental mafic volcanic rocks, a continental-type layered gabbroic complex (ca. 700 Ma), magma-mingled gabbro/quartz–monzodiorite (688 Ma), and rapakivi granites (684 Ma and 641 Ma). Deformed pillow basalts and interleaved marble lenses are likely ocean floor relicts in the Canindé Domain. Closure of the Canindé oceanic basin began at ca. 630 Ma with the intrusion of arc-type granitic plutons. Convergence of the Pernambuco-Alagoas Block and the São Francisco Craton led to deformation on the passive margins and granite emplacement in the Macururé (628–625 Ma, and 590–570 Ma), Canindé (ca. 621 Ma) and Poço Redondo-Marancó (ca. 625 Ma) domains. A small oceanic basin was most likely subducted beneath the Poço Redondo-Marancó Domain to account for the presence of 602 Ma arc-type volcanic rocks. Shortly after, exhumation of the Pernambuco-Alagoas Block and Canindé, Poço Redondo-Marancó and Macururé domains in the north led to deposition of uppermost clastic sediments in the Estância and Vaza Barris domains in the south, possibly in a foreland basin, and to final thrusting of the continental margin sedimentary rocks onto the São Francisco Craton. Our results indicate that the construction of western Gondwana involved a ca. 300 million years long history of plate breakup and collision.