Under rekonstruktion

Åsbydiabas findes i et stort antal gange i det nordlige Dalarna. Gangene forløber overvejende NNV/SSØ og skærer igennem sandstensområderne, hvorfor de benævnes som postjotniske. Det er en isotropisk bjergart bestående overvejende af augit og plagioklas, men olivin og magnetit indgår også. Teksturen er egentlig intergranulær, men kaldes oftest ofitisk, idet denne betegnelse tit benyttes i en udvidet betydning i forhold til den oprindelige. Åsbydiabas er som regel mellemkornet, så de enkelte plagioklaslister kan tydeligt ses med det blotte øje, mens olivinindholdet ofte forårsager, at områderne mellem plagioklasen forvitrer og efterlader små fordybninger.

Hovedforekomsten er en ca. 80 km lang stedvist afbrudt gang, der strækker sig fra området omkring Venjan i syd til Mossiberg i nord. Gangens bredde varierer fra få hundrede meter til ca. 4 km.

Åsbydiabas er opstået ca. 1.27 Ga i et intracratonisk riftmiljø, som herskede på denne tid, før Rodinia begyndte at samle sig. Også andre steder i Baltica var der extensionsmiljø, som førte til magmatisme, fx Vaggerydsyenit i Småland og bimodal magmatisme i Telemark.

Det er ikke kun i Dalarna, man finder mafiske gang- og dybbjergarter af samme type som Åsbydiabas. I Ångermanland kendes den som Ulvödiabas. Også i Härjedalen, Jämtland,, Sydvestfinland og Norge findes lignende bjergarter. Følgelig er bjergartens værdi som ledeblok begrænset. Samlet kaldes forekomsterne med samme alder som Åsby- og Ulvödiabas for "Central Scandinavian Dolerite Group" (CSDG). Särnadiabas er også en del af denne gruppe, men adskiller sig fra mængden ved at være augitporfyrisk.

Åsbydiabas kan forveksles med den norske nefelinsyenit, foyait, fra området nord for Larvik. Imidlertid indeholder den ikke nefelin, og mangler desuden foyaitens typiske ensretning af feldspatkornene. Det er også et godt kendetegn, at Åsbydiabas i modsætning til nefelinsyenit ofte indeholder magnetit og altså er magnetisk. Grove typer vil også kunne forveksles med Osloessexit.

Between 1271 and 1246 Ma, dolerite dykes and sills of the Central Scandinavian Dolerite Group intruded into the Fennoscandian Shield during three distinct magmatic pulses. They are distributed around five large magmatic complexes extending from Sweden to western Finland and record large-scale intracratonic tensional stress. Coeval plutonism is observed in the westernmost terrane of the Sveconorwegian orogen in southern Norway, but differs in the sense of a bimodal character and uncertain Fennoscandian ancestry of the host terrane. We report a U–Pb baddeleyite age of 1269 ± 12 Ma for a gabbronoritic member of an E-trending set of dykes, called the Moslätt Dolerites, near Lake Vättern in southern Sweden, much farther to the south than any previously known Central Scandinavian Dolerite Group rock. A similar age of approximately 1275 Ma is obtained for a meta-dolerite sheet in the Børgefjell basement window in the Scandinavian Caledonides in Mid-Norway. The initial epsilon-Hf values for these two dykes are +3.9 and +10.1, respectively, and correspond to the range of values for other occurrences of the Central Scandinavian Dolerite Group (+4.7 to +10.3). They add to the evidence that the Central Scandinavian Dolerite Group is characterized by more positive epsilon values (depleted source) than other mafic Proterozoic suites in Fennoscandia. These results extend the distribution of c. 1270–1245 Ma mafic magmatism in Fennoscandia, particularly when accounting for significant Caledonian shortening. The Central Scandinavian Dolerite Group and coeval bimodal magmatism in S Norway may represent distal magmatic events related to a Mesoproterozoic subduction along the western margin of Fennoscandia rather than hotspot (mantle plume) activity as previously suggested.

A palaeomagnetic and anisotropy of magnetic susceptibility (AMS) study has been performed on dolerite sills of the Central Scandinavian Dolerite Group (CSDG) in the Fennoscandian Shield. The dolerites occur in four previously known complexes in central Sweden and Finland and from the results of this palaeomagnetic study another complex has been identified in northern Sweden. These complexes cover an area of at least 100 000 km2 and the palaeomagnetic data suggest a small difference in time between the intrusion of the dolerites. The measurements of anisotropy of magnetic susceptibility reveal a magnetic fabric with almost horizontal foliation planes and lineations that indicate fairly uniform ca NW or SE directed magma flows. The dolerites of the CSDG are geochemically rather uniform and have compositions typical of mantle derived melts formed in continental tensional settings. In a palaeomagnetic reconstruction of Baltica versus Laurentia at ca 1.27 Ga the two continents were joined, with NE Greenland attached to NW Baltica. AMS data from a few dolerites and a basalt in NE Greenland indicate magma flow directions that in the tectonic reconstruction are more or less parallel to the flow of the dolerites in Sweden. This may suggest a common magma source located at the reconstructed contact between Baltica and Laurentia. Both the dolerites in Greenland and those in Sweden are of tholeitic composition indicating an intraplate origin, which supports the interpretation of joined continents at that time. The tensional regime, that is reflected by the huge sill complexes, is in our interpretation related to the break up of Baltica from Laurentia at ca 1.27 Ga ago.