A Mantle Plume Origin for the Scandinavian Dyke Complex: A “Piercing Point” for 615 Ma Plate Reconstruction of Baltica?

Abstract

The origin of Large Igneous Provinces (LIPs) associated with continental breakup and the reconstruction of continents older than ca. 320 million years (pre-Pangea) are contentious research problems. Here we study the petrology of a 615-590 Ma dolerite dyke complex that intruded rift basins of the magma-rich margin of Baltica and now is exposed in the Scandinavian Caledonides. These dykes are part of the Central Iapetus Magmatic Province (CIMP), a LIP emplaced in Baltica and Laurentia during opening of the Caledonian Wilson Cycle. The >1,000-km-long dyke complex displays lateral geochemical zonation from enriched to depleted basaltic compositions from south to north. Geochemical modelling of major and trace elements shows these compositions are best explained by melting hot mantle 75-250°C above ambient mantle. Although the trace element modelling solutions are nonunique, the best explanation involves melting a laterally zoned mantle plume with enriched and depleted peridotite lithologies, similar to present-day Iceland and to the North Atlantic Igneous Province. The origin of CIMP appears to have involved several mantle plumes. This is best explained if rifting and breakup magmatism coincided with plume generation zones at the margins of a Large Low Shear-wave Velocity Province (LLSVP) at the core mantle boundary. If the LLSVPs are quasi-stationary back in time as suggested in recent geodynamic models, the CIMP provides a guide for reconstructing the paleogeography of Baltica and Laurentia 615 million years ago to the LLSVP now positioned under the Pacific Ocean. Our results provide a stimulus for using LIPs as piercing points for plate reconstructions.

Timing of Breakup and Thermal Evolution of a Pre‐Caledonian Neoproterozoic Exhumed Magma‐Rich Rifted Margin

“…The new age for the Corrovarre dolerites as well as similarities in geochemistry (Roberts, ) documents that they are part of the SDC and can be correlated with the rest of the SDC in the southern segment. Tegner et al () have shown that, like the NALIP, the SDC was triggered by elevated upper mantle temperatures.…”

“…(a) Suggested paleogeographic reconstruction of Baltica and Laurentia at approximately 620 Ma, based on Tegner et al, . Red stars show the locations of LRD and ED.…”

“…During the breakup event, the SDC was emplaced along approximately 1,600 km of Baltican continental margin (e.g., Andréasson et al, , ; Tegner et al, ). During this event the sediments were metamorphosed (for convenience the prefix “meta” is omitted from the rest of the text).…”

“…The southernmost exposure of the SDC, however, is the 616 ± 3 Ma Egersund dikes, which were emplaced in the autochthonous Baltican basement (Figure ; Bingen et al, ). A recent compilation of the geochemistry of the SDC reveals a systematic zonation in trace element compositions with a geographically progressive δ‐Nb and La/Sm enrichment (E‐MORB) relative to mid‐ocean ridge basalt, implying that the formation of the magma was associated with elevated temperatures at the lithosphere‐asthenosphere boundary (Tegner et al, ).…”

Pannotia to Pangaea: Neoproterozoic and Paleozoic Orogenic Cycles in the Circum-Atlantic Region: A celebration of the career of Damian Nance

“…The break-up of Pannotia from c. 615 Ma onwards occurred as Laurentia, Gondwana and Baltica rifted from each other to form the Iapetus Ocean (Tegner et al 2019 and references therein). The ocean widened until the Late Cambrian, and then started to close following the initiation of eastdipping subduction zones (present reference frame) close to the margin of Laurentia (Cocks & Torsvik 2006).…”