Abstract

The Latest Oligocene-Pleistocene basic sheet intrusions in the Late Oligocene-Pliocene Wichianburi Sub-basin (onshore Thailand), and Eocene intrusions of the Ceduna Sub-basin (offshore southern Australia) provide examples of igneous intrusion architecture in rift and post-rift basin settings, respectively that have been imaged on 3D seismic reflection data. These examples indicate rift-related intrusions are overall smaller, have a higher aspect ratio, and tend to be more planar or transgressive in a single direction, than the saucer-shaped sills which dominate in the post-rift setting of the Ceduna Sub-basin. The long axis trend and dip-direction of most sills in the rift setting investigated tend to conform with rift structure (i.e. fault strike-directions and bedding dip and strike directions), and give a strong orientation bias, whereas orientations in the post-rift basin are more varied. The few saucer-shaped sills that formed in the Wichianburi Sub-basin are asymmetric and incompletely developed. A third area, the Kora region of the Taranaki Basin is a region where intrusions are related to a volcanic centre. This gives the intrusions a mixture of circumferential and radial intrusions related to magmatic processes (e.g. loading by the volcanic edifice, magma chamber pressure) and rift-related influences. Rift-related sills commonly form stacked arrays. Fundamental factors that affect the morphology of sills include: magma composition, volume, reservoir pressure, and the mechanical stratigraphy of the host rocks. In rifts extra complexities affecting some sills, or parts of sills include: rift structure (faults, rotated, folded bedding), basin size and morphology, stress distribution and sedimentary architecture.

Supplementary material:https://doi.org/10.6084/m9.figshare.c.4620101

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