Petrology of the Paleocene Picrites and Flood Basalts on Disko and Nuussuaq, West Greenland

• Published in: Journal of Petrology
• Main Authors: Larsen, Lotte M., Pedersen, Asger K.
• Format: Text
• Language: English
• Published: Oxford University Press 2009
• Subjects: Original Papers; Baffin Island; Greenland; Nuussuaq; Vaigat; Baffin; Iceland
• Online Access: http://petrology.oxfordjournals.org/cgi/content/short/50/9/1667; https://doi.org/10.1093/petrology/egp048

The c. 62–60 Ma rift-related Paleocene volcanic succession in West Greenland comprises voluminous picrites (the Vaigat Formation) overlain by flood basalts (the Maligât Formation). A detailed stratigraphy for the c. 3 km combined succession on Disko and Nuussuaq has been established that provides evidence of the evolution of the volcanic systems, processes and sources through time. Picrites constitute about one-third of the total erupted volume. The primary magmas for the whole succession were highly magnesian; the weighted average of 16·6 wt % MgO for the uncontaminated Vaigat Formation is a lower limit for the primary magmas. During the emplacement of the Vaigat Formation, the magmas fractionated olivine in the feeder channels before eruption but generally did not stop in magma chambers. Only minor magma batches stopped in high-level magma chambers, where many became crustally contaminated. At the transition to the Maligât Formation magma chambers developed, presumably in the lower crust. From then on, the main eruption products were basalts with compositions buffered by refilling–fractionation–tapping processes. Large-scale cyclicity can be seen, with more and less fractionated steady-state compositions. The upper part of the Maligât Formation is contaminated throughout, except for the three youngest flows. Repeated pulses of new picritic magmas can be seen in both formations. The asthenospheric mantle source was heterogeneous and the dominant component was depleted, mid-ocean ridge basalt (MORB)-like mantle with Nb/La <1. An additional, less depleted mantle component akin to the Iceland source is evident in the upper Vaigat Formation but disappeared again at the transition to the Maligât Formation. A third mantle component similar to the source for the E-type lavas on Baffin Island may be present in the earliest rocks. Melting took place in the garnet peridotite facies because the melting column was curtailed by the 100 km thick lithosphere. The picrites show coupled isotopic and elemental variations even ...