Geometrical Modelling of Igneous Intrusions: Constraints from Emplacement Mechanisms

@inproceedings{ALVARADO_RM2021,
 abstract = { Three-dimensional geological models have been widely used to assess the structure and geometry of rock units in the three dimensions (3D). Over the last few decades, significant improvements have been made in 3D modelling of folds and faults, incorporating geological knowledge into the modelling approach. Currently, igneous intrusions modelling is strongly controlled by limited available data, a do not considers any conceptual model of how intrusions are emplaced. Thus, their 3D models may not necessarily honour the geometries observed in the field. In this contribution, we present a method for stochastic simulation of igneous intrusions based on the object-distance simulation method. Our method considers conceptual knowledge of emplacement mechanisms and the use of constraints from field observations, which allow us to reproduce realistic 3D intrusive bodies. The method has two main steps. We first simulate the intrusion network object, which represents the roof or floor contacts of the body. This object is simulated using a geological model of the area, including host rock anisotropies and field observations of the intrusion contact. The second step consists of modelling the intrusion body's extent using a structural frame that provides a curvilinear coordinate system for each intrusion sheet or pluton. This structural frame has two coordinates based on the growth and propagation directions of the magma, and a third direction perpendicular to the long axis of the intrusion. We use a structural frame and a empirical geometric scaling relationships of intrusion dimensions to define a volume of uncertainty below or above the intrusion network. Within this volume of uncertainty, we compute a distance field D and a spatially correlated random field ϕ that accounts for thickness variation along the intrusion. The boundary of the intrusion is given by the isovalue 0 of the field D – ϕ. We demonstrate the potential of this method using synthetic case studies representing a sill complex and a plutonic complex. The results show that the method realistically reproduces the geometry of intrusions observed in these systems, including steps, splitting of segments, thickness changes in sills, and tabular to wedge shapes for plutons. Further work will include tests of the method using natural cases studies. },
 author = { Alvarado, Fernanda AND Ailleres, Laurent AND Grose, Lachlan AND Cruden, Sandy AND Armit, Robin },
 booktitle = { 2021 RING Meeting },
 publisher = { ASGA },
 title = { Geometrical Modelling of Igneous Intrusions: Constraints from Emplacement Mechanisms },
 year = { 2021 }
}