A Mantle Domain With a Helium Isotope Ratio of 11Ra at the Margins of the North Atlantic Igneous Province

Details A Mantle Domain With a Helium Isotope Ratio of 11Ra at the Margins of the North Atlantic Igneous Province A Mantle Domain With a Helium Isotope Ratio of 11Ra at the Margins of the North Atlantic Igneous Province

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.v13c0562m&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #V13C-0562

Physics

1032 Mid-Oceanic Ridge Processes (3614, 8416), 1038 Mantle Processes (3621), 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 8137 Hotspots, Large Igneous Provinces, And Flood Basalt Volcanism, 9325 Atlantic Ocean

Scientific paper

New data for basaltic glasses from Kolbeinsey Ridge demonstrate that for 600km north of Iceland the Mid-Atlantic Ridge samples mantle with 3He/4He of ~11 Ra (Macpherson et al., 2005). Further from Iceland, north of the Jan Mayen Fracture Zone, 3He/4He values are more typical of N-MORB. A mantle component with 11 Ra has previously been proposed to exist at around 58°N at the southern end of the Reykjanes Ridge (Hilton et al., 2000). Comparison with previous work suggests that mantle with 11 Ra may extend a further 400km south of 58°N to the Charlie Gibbs Fracture Zone, south of which 3He/4He values resemble N-MORB. The similarity in 3He/4He is mirrored in radiogenic isotope ratios suggesting that Kolbeinsey Ridge and the Charlie Gibbs to 58°N segment represent a distinct mantle domain at the margins of the North Atlantic Igneous Province. Both helium and radiogenic isotope ratios are consistent with contamination of depleted mantle by a small proportion of helium-rich material possessing high 3He/4He. There are substantial 3He/4He variations between 58°N and Iceland suggesting that any outflow of mantle from beneath Iceland has been highly asymmetric. Furthermore, if mantle outflow is responsible for high 3He/4He values on the Mid-Atlantic Ridge around Iceland then the northward flux has been negligible for a considerable period. The 11 Ra mantle domain may have been emplaced when the Kolbeinsey Ridge was initiated during the early Miocene. Alternatively, it may date from the Paleocene when magmatism became widespread throughout the North Atlantic Igneous Province. Hilton, D.R., Thirlwall, M.F., Taylor, R.N., Murton, B.J. and Nichols, A.J. (2000) Controls on magmatic degassing along the Reykjanes Ridge with implications for the helium paradox. Earth Planet. Sci. Lett. 183, 43-50. Macpherson, C.G., Hilton, D.R., Mertz, D.F., and Dunai, TJ (2005) Sources, degassing and contamination of CO2, H2O, He, Ne and Ar in basaltic glasses from Kolbeinsey Ridge, North Atlantic. Geochim Cosmochim. Acta, in press.

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