Abstract Doleritic sills, lopoliths and dykes were emplaced into the Paleoproterozoic craton in central Sweden at 1271–1264, 1259–1256 and c. 1247 Ma, a complex temporal zonation occurring in a WSW–ENE direction. The dolerites are subalkaline to alkaline and show predominantly gabbroic, with a trend towards monzogabbroic and quartz monzodioritic, compositions. Positive ɛ Nd and ɛ Hf values suggest a significant depleted mantle component in the source volume of the parental magmas. Dyke orientations indicate extension, at least locally, in a northwesterly direction, consistent with a magma flow direction determined using the anisotropy of magnetic susceptibility values. Intracratonic rifting linked to the break-up of the supercontinent Columbia, back-arc extension above a subduction boundary in a westwards-retreating mode or a mantle plume tail above a continental hotspot have all been proposed for the tectonic setting. Renewed intracratonic rifting at c. 1.14 Ga in the coastal area in northeasternmost Sweden resulted in the emplacement of alkaline ultrabasic dykes, including carbonatites (beforsites), silico-carbonatites and lamprophyres, in a north–south direction along an older shear belt. The broader tectonic setting of this extensional event is not known.

Foliated intrusions of the Early Jurassic Aishihik Plutonic Suite (APS), including the Aishihik Batholith, have been included in Stikinia and interpreted as allochthonous with respect to adjacent terranes, including the Nisling and Yukon-Tanana Terranes. The Nisling Terrane was thought to lack Early Jurassic igneous rocks. However, the Aishihik Batholith, a single plutonic body that crystallized at ca. 187 Ma, forms a west-tapering lopolith or sheet-like body that intrudes deformed strata of the Nisling Terrane. The batholith displays a margin-parallel foliation, defined by primary magmatic grains including feldspar and hornblende, that is considered to be magmatic. A parallel solid-state fabric overprints the magmatic foliation and fabric in wall rocks within 100 m of the batholith along the west (lower) margin of the batholith. This fabric is defined by gneissic banding, annealed mylonite, and by discrete shear bands. Shearing occurred at high temperatures, probably close to the granite solvus, as indicated by the breakdown of hornblende to biotite, the recrystallization of plagioclase feldspar, and by associated migmatite. Shear indicators are consistent with top-to-the-west displacement. The solid-state fabric postdates peak regional deformation of the Nisling Terrane and is inferred to have developed during late stage ballooning of the intrusion. A model of intrusion of the Nisling Terrane by the Aishihik Batholith, with subsequent ballooning of the batholith, is consistent with the lopolithic shape of the batholith, the distribution of solid-state fabrics, the shear sense and near-solvus temperatures during solid-state deformation, the presence of xenoliths similar to that of the Nisling Terrane in the batholith, and the development, in the Nisling Terrane, of a hot-side-up aureole beneath the batholith. Because the Aishihik Batholith intrudes the Nisling Terrane, (1) the APS cannot be considered diagnostic of Stikinia, and (2) the Nisling Terrane cannot be considered as lacking Early Jurassic igneous rocks. The APS may represent part of an igneous overlap assemblage that links together terranes of the Intermontane belt. Alternatively, Early Jurassic intrusions may have developed in response to the subduction of oceanic crust separating some of the Intermontane terranes.

Gilbert (1877) proposed that the level of emplacement of laccoliths is controlled by the density contrast between rising magma and the weighted mean density of the overburden. For felsic laccoliths, his hypothesis is strongly supported by gravity surveys of a number of laccolith groups. Epizonal felsic laccoliths are consistently found to have zero density contrast with the host rocks. Constraining the emplacement level provides a basis for analysis of the growth of laccoliths. Mechanical analysis suggests that the diverse shapes of laccolithic intrusions observed in the field can be represented by a continuous series of intrusion modes between two distinct end members. The simplest end member is an epizonal intrusion formed by a single sill that acts mechanically as a vertical punch. Punched laccoliths are characterized by flat tops, peripheral faults, and steep or vertical sides. The other end member results from the intrusion of multiple sills stacked vertically in a fashion suggestive of a Christmas tree. The multiple-level loading results in plastic deformation of the country rock. Christmas-tree laccoliths lack peripheral faults and have a characteristic rounded dome appearance on the surface. The floor of these laccoliths may, or may not, sag. Gilbert’s (1877) ideal laccolith falls between these two end members. The end members of the laccolith growth series are treated as boundary value problems in continuum mechanics. Geometrically and materially nonlinear finite element analysis is used to solve the boundary value problems. Field observation, a physical model, and the theoretical models provide convergent answers to the mechanical analysis of the growth of laccoliths. As a check on the theoretical models, a gazetteer of the dimensions and locations of approximately 900 laccoliths is included. Of these, approximately 600 are located in the United States. If North America represents a statistically valid sample, then there must be between 5,000 and 10,000 laccoliths around the world.