Post-rift tectonic activity revealed by dyke intrusion in an Aptian granite emplaced in the coastal zone of the marginal Pernambuco Basin (NE Brazil)

Understanding magmatic dyke emplacement requires examining the physical conditions that allow magma to propagate through the crust, specifically magma behavior, stress fields, and structural inheritance. This study focuses on the Cabo de Santo Agostinho Granite in the Pernambuco Basin, NE Brazil. As part of the Early Cretaceous Ipojuca Magmatic Suite, this granite hosts rhyolitic dykes and pseudotachylyte veins, providing a record of shallow-crustal interactions during the final stages of the South Atlantic opening. By integrating facies analysis, structural characterization, and tension estimates, we investigated whether these intrusions were linked to the final rift stages. Nine lithofacies were identified within a monzonitic batch, including dykes, injection veins, and enclaves. Structural relationships indicate that dykes propagated along pre-existing fractures independent of the stress fields associated with Cretaceous rifting. The sequence began with larger dykes followed by minor rotated intrusions. Magmatic overpressure estimates suggest a source reservoir at approximately 5-7 km depth. The pseudotachylytes likely resulted from seismic fault reactivation, where hydrous minerals like amphibole and biotite favored localized melting. Our data suggest these dykes represent the final magmatic pulses of a shallow reservoir during the plutonic evolution of the granite. Ultimately, deformation analysis confirms the intrusions occurred during the post-rift stage and were governed by local stress regimes. • Dikes controlled by local stress fields rather than regional stress fields. • Shallow magma chamber rupture triggering dike initiation. • Anomalous pseudotachylyte generation due to fault activity in amphibole-rich monzonite. • Magma pulses sourced from mantle and crustal reservoirs.