Geodynamics of rift–plume interaction in Iceland as constrained by new 40Ar/ 39Ar and in situ U–Pb zircon ages

• Published in: Earth and planetary science letters Vol. 311; no. 1; pp. 28 - 38
• Main Authors: Martin, E., Paquette, J.L., Bosse, V., Ruffet, G., Tiepolo, M., Sigmarsson, O.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-11-2011; Elsevier
• Subjects: Earth Sciences; geochronology; geodynamic evolution; Geology; Iceland; Mantle; mantle plume–ridge interaction; Marine; Plumes; Radioactive age determination; Relocation; Ridges; rift propagation; Sciences of the Universe; Spreading; spreading rate; Zircon; AN, North Atlantic; ANE, Atlantic, Iceland; ANE, Atlantic, Kolbeinsey Ridge; A, Mid-Atlantic Ridge; geochronology; geodynamic evolution; rift propagation; Iceland; mantle plume–ridge interaction; spreading rate
• ISSN: 0012-821X; 1385-013X
• DOI: 10.1016/j.epsl.2011.08.036

The interaction between a rift zone and a mantle plume leads to exceptional situations in Iceland where the island is 1.5 wider than expected, given the North-Atlantic spreading rate. In order to give a better idea of the timeframe of this evolution, we present 32 new
40Ar/
39Ar and in-situ U–Pb dating on zircon from 16 volcanic systems located from the west to east coasts of Iceland. The North Iceland Rift Zone (NIRZ) was initiated at least 12
Ma ago. Furthermore, during these last 12
Ma, the NIRZ half spreading rate was between 0.7 and 1.2
cm/yr and it propagated to the south at a rate of 1.0–1.2
cm/yr. The excess width of Iceland can thus not be explained by faster spreading rate in the past. Here we discuss a model that explains the ~
200
km ‘excess’ of crust, taking into account the eastward relocation of the rift zone and corresponding older crustal capture over the course of Iceland's geological history. The most recent rift relocation is dated at approximately 6
Ma at Snæfellsnes Peninsula in the west, whereas the oldest volcanic systems (15–13
Ma) from the extreme north east of Iceland were most likely generated at the Kolbeinsey ridge north of Iceland rather than in the NIRZ itself.
The need for rift relocations and crustal capture to explain the width of Iceland strongly suggests that during rift–plume interaction the mantle plume plays an active role. It forces the active rift zone to be frequently relocated by rift jumps above its center leaving inactive rift zones as older synclines in the geological record. This result in an eastward position of the rift zone in Iceland relative to the North Atlantic ridge, and it can be predicted that in a few tens of millions of years the Mid-Atlantic ridge and the Icelandic plume may become decoupled.
►
40Ar/
39Ar and in-situ U-Pb zircon ages up to 15Ma measured in the NE of Iceland. ► Geodynamic evolution of the rift-plume interaction, from which results Iceland. ► NIRZ spreading rate over the last 12Ma : 0.7-1.1 cm/yr. ► NIRZ propagation rate to the South over the last 12Ma: 1.0-1.1 cm/yr. ► The future of Iceland is an intra-plate context.