Table 3.

Variations in factors influencing sill morphology in three tectonic settings

VariablePost-rift intrusion into post-rift basin (e.g. Ceduna Sub-Basin)Post-rift intrusion into synrift basin (e.g. Kora area, Taranaki Basin)Synrift intrusion into synrift basin (e.g. Wichianburi Sub-basin)
Magma emplacement rateImportantImportantImportant
Magma volumeImportantImportantImportant
Magma physical propertiesImportantImportantImportant
Stratigraphic variationsTypically gradualGradual to abrupt, often structurally controlledGradual to abrupt, often structurally controlled
Degree of lithificationVariable, tending to unlithified to moderately lithifiedModerately to well lithifiedUnlithified to well lithified
Depth of intrusionOften c. 2 km to near surfaceVariable≥7 km to near surface
Presence of major mechanical contrasts in sectionCommonly minor with generally gradual changes in lithology, but some basins can exhibit significant contrasts (e.g. change from post-rift evaporates, to carbonates, to clastic deposits)Present (e.g. synrift–pre-rift unconformity, lateral and vertical changes from lacustrine shales to sand-prone fluvial–alluvial–deltaic facies)Present (e.g. synrift–pre-rift unconformity, lateral unconformity, lateral and vertical changes from lacustrine shales to sand-prone fluvial–alluvial–deltaic facies)
Variable dip of beddingMinor to absent; bedding gently inclined to subhorizontal. Exceptions occur where gravity-driven deformation has occurredImportant; rotation of bedding by major faults in half-grabens (commonly 10–20°, exceptionally up to 40° or higher), more local rotation by fault propagation folds, local strike-slip faults, oblique faults, folding related to variable fault displacementImportant; rotation of bedding by major faults in half-grabens (commonly 10–20°, exceptionally up to 40° or higher), more local rotation by fault propagation folds, local strike-slip faults, oblique faults, folding related to variable fault displacement
Restricted basin shapeNoImportant (e.g. major half-grabens typically 40–70 km long, 20–50 km wide, with internal tilted fault blocks)Important (e.g. major half-grabens typically 40–70 km long, 20–50 km wide, with internal tilted fault blocks)
FaultsMinor to absent (e.g. numerous polygonal faults, but low displacement some tens of metres; other faults tens to hundreds of metres displacement), except where major gravity-driven systems are presentMajor (basin-bounding faults typically >1 km displacement, numerous synrift faults of various types related to crustal extension, formed above dyke swarms, gravity-driven structures)Major (basin-bounding faults typically >1 km displacement, numerous synrift faults of various types related to crustal extension, formed above dyke swarms, gravity-driven structures)
Influence of tectonic stress fieldMinor; typically low amount of fault activityMinor(?); stress field unrelated to riftingMajor; stress field driving lithospheric extension