Fixity of the Iceland “hotspot” on the Mid-Atlantic Ridge: Observational evidence, mechanisms, and implications for Atlantic volcanic margins

Abstract

The Iceland anomaly has been attributed to a deeply rooted and fixed mantle plume, and Early Tertiary magmatism in the North Atlantic Igneous Province (NAIP) has commonly been interpreted to relate to an ancient expression of the same plume. We challenge these concepts. A major problem with attributing the Iceland anomaly to a fixed plume is the lack of evidence for a hotspot track. Although the GreenlandFaeroe Ridge has been suggested to be the hotspot track, its symmetric and continuous construction instead suggests in situ development on the plate boundary. Magmatism in the NAIP occurred in two phases, distributed in approximately perpendicular belts. The first phase (ca. 62-58 Ma) occurred along a north-west belt through the British Volcanic Province to west Greenland. We relate this phase to a transient and failed rift, intermediate in time and space between seafloor spreading in the Labrador Sea and the northeast Atlantic. The second phase (ca. 56-53 Ma) followed the incipient northeast Atlantic plate boundary. Both magmatic phases can therefore be associated with plate tectonics. Likewise, the north Atlantic-Arctic breakup can be explained as a natural outcome of plate tectonics and lithospheric strength distribution. We follow other recent research in suggesting that the voluminous magmatism during NAIP phase 2 is related to reactivation and opening along the Caledonian orogen. Specifically, we point to a close correspondence between the reactivated orogen and the north Atlantic volcanic passive margins, and suggest that the extreme magmatism could stem from the melting of eclogitic material, either residing in remnants of the CaledonianAppalachian orogenic root or within a delaminated root. Extending this idea, we postulate as a testable hypothesis that volcanic margins are the natural products of the Wilson Cycle (i.e., opening of sutures). We have tested the hypothesis on the north, central, and south Atlantic Ocean and have found a broad correlation between volcanic margin segments and reopened Late Neoproterozoic-Phanerozoic fold belts.

Thermochemical Heterogeneity and Density of Continental and Oceanic Upper Mantle in the European‐North Atlantic Region

“…Positive Reduced RMG anomalies are restricted largely to the East Greenland margin (+40 + 160 mGal) and the Greenland‐Iceland‐Faroe Ridge (GIFR) across the Atlantic Ocean (0 + 50 mGal). The geodynamic origin of the GIFR, which has a ~25‐ to 30‐km‐thick crust remains enigmatic (Lundin & Dore, ; Parkin & White, ). Our results suggest that the deep structure of the GIFR is not fully symmetric: The major high‐density anomaly is along the Greenland margin, where it is apparently associated with the North Atlantic LIP.…”

The North Atlantic Igneous Province: A review of models for its formation

“…Details of the timing, location, structure, and composition of the postulated plume in the Early Paleogene, however, remain controversial. Lundin and Doré (2005) questioned the validity of the idea of pin-pointing the suggested plume locality.…”

“…This evolution of the mantle plume concept has been addressed by several authors (e.g., Anderson and Natland, 2005;Foulger, 2005), and alternative hypotheses on NAIP formation have been formulated over the last 10 years or so. These include moderately elevated mantle temperatures, fertile patches in the upper mantle, and small-scale convection (e.g., Boutillier and Keen, 1999;King and Anderson, 1995;van Wijk et al, 2001;Korenaga, 2004;Anderson and Natland, 2005;Lundin and Doré, 2005; http://www.mantleplumes.org).…”

Treitel Ridge: A unique inside corner hogback on the west flank of extinct Aegir spreading ridge, Norway basin

“…This is consistent with a "rapid death" model for extinct spreading axes: The actual extinction date for e.g., the Mid-Labrador Sea axis and similar dead spreading centers (e.g., Aegir Ridge) are poorly constrained, due to the limits of resolving power of magnetic anomalies recorded at very slowspreading. In any case, we believe the formation of TR had nothing to do with the postulated Iceland mantle hotspot or plume-the TR, as perhaps also other features of the Iceland "hotspot" region (e.g., Foulger, 2002;Foulger et al, 2005;Lundin and Dore, 2005;see Meyer et al, 2007 for in-depth evaluations of plume and non-plume models)-was produced by plate tectonic processes. The excess magmatism in the region has been attributed in some non-plume models to remelting of previously subducted, fertile, Caledonian-aged eclogitic crust.…”

“…Moreover, an OBS survey from Kolbeinsey Ridge to the Jan Mayen Ridge failed to find evidence for an extinct axis (Kodaira et al, 1998). Different "tracks" have been computed for the Iceland hotspot by different investigators (e.g., Lawver and Mueller, 1994), but as pointed out by Lundin and Dore (2005), there is little evidence for the predicted time-transgressive trace that should extend from Iceland across Greenland. When TR was formed ca.…”