The Davis Strait BLIP: Tenuous relationships to deep mantle plume activity and NAIP

Category Petrology
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Clarke, D. Barrie
Holding Date 20 September 2008

Prior to the initiation of sea-floor spreading in latest Mesozoic to earliest Cenozoic times, the Labrador Sea axis had been an intermittent, but long-lived (>150 My), locus of alkaline magmatism. Within a short time span of 1-2 My in the Paleocene, and coeval with the onset of sea-floor spreading in the Labrador Sea, massive outpourings of uniquely depleted picritic tholeiites occurred in the vicinity of Davis Strait, and the axis of sea-floor spreading in the Labrador Sea may have extended beyond Davis Strait into Baffin Bay. The chemical characteristics of the Davis Strait picrites (MgO = 18-21 wt. %; K2O = 0.01-0.20 wt. %; 87Sr/86Sri ≈ 0.7030; εNdi ≈ +5.2-8.6; 3He/4He < 49.5RA) are inconsistent with derivation from a fertile mantle plume, and more in keeping with derivation by extensive melting of highly depleted asthenospheric mantle. Thus, picritic volcanic activity in Davis Strait was a temporally brief, volumetrically excessive, chemically anomalous, and genetically unique BLIP (Baby Large Igneous Province) on the otherwise unremarkable Labrador Sea spreading centre. The Davis Strait BLIP is at least spatially, if not also causally, related to the long Ungava Fault Zone (leaky transform fault) that facilitated ascent of the primary picritic magmas to the surface. Furthermore, the spatial, temporal, and compositional mirror planes of symmetry through Iceland for East Greenland — Scotland, and through Davis Strait for Baffin Island — West Greenland, are distinctly different and do not easily fit a single comprehensive genetic model for NAIP volcanism.