Sedimentary rock deformations induced by magmatic intrusions: intrusion classification and mechanisms

Abstract

Structural geology has been adapted to the modem concept af global tectonics, in as much as a given ser af structural styles distinguishes a specific tectonic habitat within a lithospheric plate. The purpose of this paper is to define and classify the structural styles relatedta magmatic intrusians in the extensional basin setting. During the emplacement and growth of some igneous bodies, the original stress field may be locally modified to generate a new stress field that is able to deform lhe sedimenlary host rocks. These deformations were studied and classified based on geometrical fetltures of magmatic bodies and the associated structural components in the wall rocks. The study area included Brazifian sedimentary basins of Paleozoic age, namely, Solimões, Amazonas, Maranhão, and Paraná. Field work was restricted to lhe last two. Fourteen structural styles were defined in these basins, related to dykes, sills, laccoliths, bysmaliths, wedges, and magmatic apophyses. Recognition of the seismic expression of structural styles associated with igneous intrusions was performed bycomparing outcrop data with 
geophysical profiles. Computer simufation was used as an aid in this phase ofthe research. A goodcorrelation between outcrop 
and seismic data was obtained in most of lhe structural styles, According to the model offield stress changes and structuration of host rocks proposed here, some deformations take place under plastic flow conditions, while others present brittle behavior, depending on the spatial relationship between host rocks and igneous bodies. The repeatability of structural styles across time 
and space lends the model a predictive character lhat can be useful in lhe exploration of hydrocarbon deposits. Some structural 
styles associated to the emplacement of magmatic bodies are able to trap oil, mainly in tectonically quiet sedimentary basins. The term "intrusive tectonics" is proposed to characterize the environment of deformatian related to the emplacement of igneous intrusions,