<p>The advanced stages of the Neoproterozoic Brasiliano orogeny in western Gondwana led to significant crustal reworking and extensive peraluminous magmatism, with many plutons spatially associated with shear zones. This study applies a multi-methodological approach (airborne magnetic surveys, structural analysis, anisotropy of magnetic susceptibility analyses, and U–Pb zircon dating) to the Parnamirim Pluton (Central Domain of the Borborema Province, northeastern Brazil). The pluton is located between the West Pernambuco (E–W, dextral) and Parnamirim (NE–SW, sinistral) shear zones and consists of three main pulses (PP1, PP2, and CV) of peraluminous syenogranites to monzogranites, with magnetic susceptibility controlled by paramagnetic minerals. The NE–SW-striking magmatic, solid-state and magnetic foliations are steeply dipping to subvertical, reflecting syn- to post-emplacement deformation in response to strain caused by the regional deformation field. Magmatic to high-temperature solid-state microstructures dominate in the eastern PP1 unit, while high-strain and high-temperature solid-state deformation microstructures, characterized primarily by grain boundary migration recrystallization, show increasing strain in the western PP2 unit. Elongate country rock xenoliths indicate that pluton emplacement occurred initially by fracture propagation and evolved into sheet amalgamation. Pluton growth was controlled by NE–SW horizontal extension resulting from the combined motion of the West Pernambuco and Parnamirim shear zones, progressing westward, as constrained by the U–Pb zircon ages of PP1 (569 ± 1&#xa0;Ma) and PP2 (559 ± 2&#xa0;Ma). The age of the Parnamirim Pluton is similar to those of other granitoids in the Borborema Province and the &#xa0;Benino-Nigerian Shield, indicating a large-scale magmatic and tectonic event.</p> Graphical abstract <p>Simplified model of the multi-stage intrusion and deformation of the Parnamirim Pluton. The schematic drawing illustrates: the sheet-like intrusion, consistent with the vertical foliation of the host rock (Salgueiro Complex); the initial intrusion took advantage of the foliation planes of the host rocks, facilitating the initial accommodation of the magmatic sheets which provides space and favorable thermal anisotropy for the advancement of the intrusion through the amalgamation of sheets; and the displacement of younger and hotter sheets to the west, favoring strain partitioning during the deformation of the pluton and allowing magmatic textures to be preserved in the eastern part. Additionally, the growth of the pluton was controlled by NE-SW horizontal extension resulting from the combined opposite motion of the West Pernambuco and Parnamirim shear zones, in response to NNW-SSE regional shortening. White arrows represent the transpressive context</p>

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Multistage emplacement of a composite intrusion: magnetic fabric and zircon U–Pb age of the Parnamirim Pluton, NE Brazil

  • C. H. F. S. Neves,
  • S. P. Neves,
  • V. P. Ferreira,
  • A. N. Sial,
  • B. T. A. Lima,
  • D. H. Ardila,
  • R. Siqueira

摘要

The advanced stages of the Neoproterozoic Brasiliano orogeny in western Gondwana led to significant crustal reworking and extensive peraluminous magmatism, with many plutons spatially associated with shear zones. This study applies a multi-methodological approach (airborne magnetic surveys, structural analysis, anisotropy of magnetic susceptibility analyses, and U–Pb zircon dating) to the Parnamirim Pluton (Central Domain of the Borborema Province, northeastern Brazil). The pluton is located between the West Pernambuco (E–W, dextral) and Parnamirim (NE–SW, sinistral) shear zones and consists of three main pulses (PP1, PP2, and CV) of peraluminous syenogranites to monzogranites, with magnetic susceptibility controlled by paramagnetic minerals. The NE–SW-striking magmatic, solid-state and magnetic foliations are steeply dipping to subvertical, reflecting syn- to post-emplacement deformation in response to strain caused by the regional deformation field. Magmatic to high-temperature solid-state microstructures dominate in the eastern PP1 unit, while high-strain and high-temperature solid-state deformation microstructures, characterized primarily by grain boundary migration recrystallization, show increasing strain in the western PP2 unit. Elongate country rock xenoliths indicate that pluton emplacement occurred initially by fracture propagation and evolved into sheet amalgamation. Pluton growth was controlled by NE–SW horizontal extension resulting from the combined motion of the West Pernambuco and Parnamirim shear zones, progressing westward, as constrained by the U–Pb zircon ages of PP1 (569 ± 1 Ma) and PP2 (559 ± 2 Ma). The age of the Parnamirim Pluton is similar to those of other granitoids in the Borborema Province and the  Benino-Nigerian Shield, indicating a large-scale magmatic and tectonic event.

Graphical abstract

Simplified model of the multi-stage intrusion and deformation of the Parnamirim Pluton. The schematic drawing illustrates: the sheet-like intrusion, consistent with the vertical foliation of the host rock (Salgueiro Complex); the initial intrusion took advantage of the foliation planes of the host rocks, facilitating the initial accommodation of the magmatic sheets which provides space and favorable thermal anisotropy for the advancement of the intrusion through the amalgamation of sheets; and the displacement of younger and hotter sheets to the west, favoring strain partitioning during the deformation of the pluton and allowing magmatic textures to be preserved in the eastern part. Additionally, the growth of the pluton was controlled by NE-SW horizontal extension resulting from the combined opposite motion of the West Pernambuco and Parnamirim shear zones, in response to NNW-SSE regional shortening. White arrows represent the transpressive context