Dispersion of a continental crust component by the Iceland plume Reidar G. Trønnes 1,2 Trond H. Torsvik 1 1 Centre for Earth Evolution and Dynamics (CEED), Univ. Oslo 2 Natural History Museum, Univ. Oslo

Iceland plume - interacts with the MAR-system  makes it difficult to estimate plume flux - Earth’s largest plume, 5-10 times the flux of the Hawaii plume (Jones et al. 2014, EPSL), based on the size and crustal thickness of the Iceland plateau and distribution of V-shaped ridges

Gibbs FZ JM FZ Exceptionally thick oceanic crust Melting and volcanic productivity is modulated by: - Episodic plume flux, resulting in V-shaped ridges - Glacio-isotatic cycles decompression melting under Iceland is sensitive to incremental pressure variations caused by glacial cycles

Evidence for laterally deflected and episodic plume flow from Iceland Jones et al. (2002, GGG) Breivik et al. (2006, JGR) V-shaped ridges: extending radially for about 1000 km

Diachronous V-shaped ridges record plume pulses

Lateral extent RR: >1200 km KR: >900 km (diameter: >2000 km) Periodicity: 5-6 Ma in phase with uplift of Iceland plateau and rift jumps in Iceland

Evidence for continental crust under SE Iceland 1. Eastern Flank Zone (EFZ), especially the Öræfajökull central volcano, has a unique isotopic composition: - high 87 Sr/ 86 Sr and 207 Pb/ 204 Pb ratios at a given 143 Nd/ 144 Nd - EM2-like signature (EM2: recycled terrigenous sediments) 2. The possible extension of the JMM under Iceland, based on plate reconstructions 3. Thick crust under SE Iceland Torsvik et al. (2015, PNAS)

Simplified evolution model NE Atlantic Torsvik et al. (2015)

Iceland: rift jumps - plume position - Eastwards rift jumps at 15, 7 and 2 Ma the NE Atlantic plate boundary moves towards NW relative to plume position

Iceland: rift jumps - plume position - Eastwards rift jumps at 15, 7 and 2 Ma the NE Atlantic plate boundary moves towards NW relative to plume position - Likely plume position km W or WSW of Öræfajökull Shorttle et al. (2010, GGG); Shen et al. (2002, EPSL) P660s  P410s differential times IASP91  observed (Shen et al. 2002, EPSL)

Central Iceland locus of: thickest crust minimum V P minimum V S P660s  P410s differential times IASP91  observed Shen et al. (2002, EPSL) Torsvik et al. (2015, PNAS) From: Wolfe et al. (1997, Nature) High heat flow and volcanic production in the Grimsvötn-Bárðarbunga-Kverkfjöll central volcanoes near the ERZ-NRZ confluence Crustal thickness model

The Eastern Flank Zone (Öræfajökull) geochemical anomaly - Homogeneous isotopic comp. throughout the basalt to rhyolite compositional range - If caused by CC-contamination: must occur in primitive parental melt - deep, near Moho - Evolved rocks derived mainly by crystal fractionation (e.g. Selbekk and Trønnes, 2007; Martin and Sigmarsson, 2010)

Sr-Nd-Pb isotope characteristics Mixing array: MIB → ERZ → EFZ (in the EM2 direction) The array cross-cuts other NE-Atlantic mixing arrays : purple, blue, light blue trend lines and points in distinct Pb-isotopic directions: towards: low 206/204 Pb high 206/204 Pb intermediate 206/204 Pb

Sr-Nd-Pb isotopic model for the evolution: MIB → ERZ → EFZ → CC ERZ: 0-2 % CC EFZ: 2-6% CC

A plume dispersion model Shallow lateral flow towards ERZ (mostly via Grimsvötn and Bárðarbunga central volcanoes) from the deep plume channel, which must underlie parts of the JMM

Rift jumps and deep burial of the JMM Model hypothesis: Shallow plume flow directed to the NW-side of the JMM-E since the JMM initiaion (30 Ma to present) - Asymmetric plume flow, directed towards dying rift zone - Repeated opening of new rift zones at the NW-side of the original flank zone and JMM-E during

Rift jumps and deep burial of the JMM

Conclusions Geochemical evidence for deeply buried JMM under SE Iceland The JMM obtained a flank zone position at the eastern margin of the new rift zones at the time of rift zone jumps at 24, 15, 7 and 2 Ma (plate spreading removes the JMM from the rift zone margin at 10 km/Ma) Previously estimated Iceland plume position in the Grimsvötn-Bárðarbunga-Kverkfjöll area can be explained by a plume flow and melting anomaly in the ERZ-NRZ-confluence region