Dispersion of a continental crust component by the Iceland plume Reidar G. Trønnes 1,2 Trond H....
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![Page 1: 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),](https://reader035.fdocuments.in/reader035/viewer/2022062719/56649ee55503460f94bf5861/html5/thumbnails/1.jpg)
Dispersion of a continental crust component by the Iceland plume
Reidar G. Trønnes1,2
Trond H. Torsvik1
1 Centre for Earth Evolution and Dynamics (CEED), Univ. Oslo2 Natural History Museum, Univ. Oslo
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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
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Gibbs FZ
JM FZ
Exceptio
nally th
ick oce
anic
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
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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
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Diachronous V-shaped ridges record plume pulses
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Lateral extent
RR: >1200 km KR: >900 km (diameter: >2000 km)
Periodicity: 5-6 Ma
in phase with uplift of Iceland plateauand rift jumps in Iceland
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Evidence for continental crust under SE Iceland
1. Eastern Flank Zone (EFZ), especially the Öræfajökull central volcano, has a unique isotopic composition:
- high 87Sr/86Sr and 207Pb/204Pb ratios at a given 143Nd/144Nd
- 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)
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Simplified evolution model NE Atlantic
Torsvik et al. (2015)
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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
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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 35-60 km W or WSW of Öræfajökull Shorttle et al. (2010, GGG); Shen et al. (2002, EPSL)
P660s - P410s differential timesIASP91 - observed (Shen et al. 2002, EPSL)
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Central Iceland locus of:
thickest crust minimum VP
minimum VS
P660s - P410s differential timesIASP91 - observed Shen et al. (2002, EPSL)
Torsvik et al. (2015, PNAS)
From:Wolfe et al. (1997, Nature)
High heat flow and volcanic production inthe Grimsvötn-Bárðarbunga-Kverkfjöll centralvolcanoes near the ERZ-NRZ confluence
Crustal thickness model
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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)
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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 206/204Pb
high 206/204Pb
intermediate 206/204Pb
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Sr-Nd-Pb isotopic model for the evolution:
MIB → ERZ → EFZ → CC
ERZ: 0-2 % CC
EFZ: 2-6% CC
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A plume dispersion modelShallow lateral flow towards ERZ (mostly via Grimsvötn and Bárðarbunga central
volcanoes) from the deep plume channel, which must underlie parts of the JMM
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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
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Rift jumps and deep burial of the JMM
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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 areacan be explained by a plume flow and melting anomaly in the ERZ-NRZ-confluence region