An alkaline rock province linking Europe and North America

Abstract

Lower Paleozoic carbonatites associated with the St. Lawrence graben system are correlated with carbonatites of similar age (565 m.y.) in Greenland and Scandinavia. The correlation is well established in Canada where the intrusions all occur along a continuous rift system. The reconstruction of the whole province is made possible by restoring the continents to the positions they occupied prior to their separation.The combination of unique petrologic character, age, and structural setting shows that these rocks belong to a single alkaline rock province, defined by a rift system extending at least from central Canada to eastern Sweden that was active throughout its length about 565 m.y. ago.Periodic intrusion of alkaline rocks has occurred later, on both continents, associated with the components of the fracture system. In eastern Canada, alkaline rocks occur locally with ages of 520, 450, 300, and 110 m.y. in addition to the widespread 565 m.y. event.

Between carbonatite and lamproite—Diamondiferous Torngat ultramafic lamprophyres formed by carbonate-fluxed melting of cratonic MARID-type metasomes

“…610 to 550 Ma; Larsen and Rex, 1992;Heaman, 2005) at the southern and northern NAC margins, respectively. In the greater North Atlantic region, Late Neoproterozoic UML/carbonatite occurrences are known from the St. Lawrence Valley Rift system (e.g., Doig and Barton, 1968;Gittins et al, 1975) and the Scandinavian Peninsula (e.g., Doig, 1970;Brueckner and Rex, 1980;Dahlgren, 1994).…”

“…610 and 550 Ma (Doig, 1970;Torsvik et al, 1996). Numerous carbonatite intrusions, many of which are associated with carbonate-rich UML magmas, were emplaced through zones of persistent lithospheric weakness such as the present-day St. Lawrence Valley and Labrador Sea rift systems (Doig and Barton, 1968;Larsen and Rex, 1992;Tappe et al, 2007).…”

Stratigraphical section through Lower Cambrian at Söderfjärden, Vaasa, western Finland

“…The Fen alkaline intrusion in southern Norway has also been dated at 585 Ma (Oftedahl 1980). Iivaara, c. 500 km NE of Söderfjärden, is 430 Ma old (Doig 1970).…”

Palaeopangaea in Meso-Neoproterozoic times: The palaeomagnetic evidence and implications to continental integrity, supercontinent form and Eocambrian break-up

“…A key indicator is the initiation of continental rifting and passive margin formation which is recognised as a worldwide event beginning at ∼0.62 Ga (Bond et al, 1984). This is temporally linked to widespread alkaline igneous activity beginning at ∼0.6 Ga, magmatism which is presumably a signature of the subcrustal heat accumulation (and possibly mantle plume up-rise); the spatial focus of the activity close to the subsequent rifting indicates that it contributed to weakening and subsequent rifting of the lithosphere (Doig, 1970;Piper, 1987). Formation of hot and buoyant spreading ridges with stretching and attenuation of new continental margins combined to cause the flooding of marine shelves into Early Cambrian times.…”