Emplacement mechanisms of the Córrego Seco post-collisional mafic pluton revealed by AMS and gravity data, Brasília orogenic belt

Abstract

The Corrego ́ Seco (CS) pluton, located in the southern Brasília Orogenic Belt (BOB), central Brazil, represents a key expression of post-collisional mafic magmatism emplaced during the late Ediacaran (~630–610 Ma). The intrusion exhibits inverse zoning, with a gabbroic core surrounded by dioritic margins, and abundant mingling and hybridization textures that point to incremental construction by multiple magma pulses. To constrain its emplacement mechanisms, we integrate anisotropy of magnetic susceptibility (AMS), anisotropy of anhysteretic remanent magnetization (AARM), petrographic analyses, and gravity data. AMS and AARM fabrics reveal a concentric magnetic foliation pattern around the gabbroic core within a westward-dipping tabular pluton, reflecting magma flow and late-stage solid-state overprints. Petrographic observations highlight localized crystal- supported deformation along pluton margins and in adjacent country rocks, consistent with reduced melt frac- tions during final crystallization. Gravity modeling based on 73 new stations and 3D inversion demonstrates a westward-dipping geometry with thickened roots toward the west. These structural and geophysical features indicate that pluton emplacement was controlled by crustal-scale discontinuities and shear zones, with the asymmetric westward-dipping geometry being inconsistent with simple diapiric ballooning models. Integration of magnetic, petrographic, and gravimetric evidence supports a model of stepwise pluton assembly, where magma ascent was strongly controlled by inherited suture at the boundary between the Arenopolis ́ Arc and the Anapolis ́ –Itauçu Complex. This interpretation provides a key tectonic constraint, indicating that magmatism postdated the main suturing processes during the terminal stages of Gondwana amalgamation.