Intrusion Emplacement Characteristics of the Passive Continental Margin Basin, Offshore Southern Brazil

The emplacement of intrusions (e.g., sills, dikes, laccoliths) is a key process shaping the structural evolution of passive continental margin basins, and their emplacement characteristics are crucial for understanding magmatism-driven deformation of the basin fillings. This study focuses on the intrusion emplacement characteristics in a passive continental margin basin offshore southern Brazil, aiming to elucidate the spatiotemporal patterns of intrusions and their genetic links with the stratigraphic evolution of the basin.

We integrated 3D seismic data with multi-disciplinary datasets from drilled boreholes, including petrophysical, geochronological, and petrographic information. A comprehensive interpretation approach was adopted, incorporating insights from structural geology, stratigraphy, and volcanology to construct a unified model for intrusion emplacement and its coupling relationship with basin filling evolution.

Seismic interpretation reveals that igneous intrusions (sills, dikes, laccoliths) in the study area exhibit distinct high-amplitude responses on seismic profiles, which facilitates the identification of their geometric shapes and spatial distributions—key characteristics of intrusion emplacement. The emplacement of these intrusions induced significant uplift and arching of pre-eruptive strata in the sub-volcanic zone. By analyzing the spatiotemporal patterns of sedimentary filling, variations in sedimentary thickness, the spatial location of volcanic craters, and the relationship between sedimentary rocks and intrusions beneath volcanic cones, we successfully constrained the emplacement period of intrusions, the process of basin subsidence, and the active period of magmatism. Additionally, multiple types of sediment-magma interactions were identified, which further reflect the response of sedimentary systems to intrusion emplacement and provide supplementary evidence for understanding emplacement characteristics.

This study systematically clarifies the intrusion emplacement characteristics of the passive continental margin basin in offshore southern Brazil, providing critical insights into the mechanisms of intrusion emplacement in similar geological settings. It also offers a valuable reference for understanding magmatism-driven basin filling evolution in global passive continental margin basins.