186Os and 187Os enrichments and high-3He/4He sources in the Earth’s mantle: Evidence from Icelandic picrites

Other

Scientific paper

Rate now

  [ 0.00 ] – not rated yet Voters 0   Comments 0

Details

20

Scientific paper

Picrites from the neovolcanic zones in Iceland display a range in 187Os/188Os from 0.1297 to 0.1381 (γOs = + 2.1 to +8.7) and uniform 186Os/188Os of 0.1198375 ± 32 (2σ). The value for 186Os/188Os is within uncertainty of the present-day value for the primitive upper mantle of 0.1198398 ± 16. These Os isotope systematics are best explained by ancient recycled crust or melt enrichment in the mantle source region. If so, then the coupled enrichments displayed in 186Os/188Os and 187Os/188Os from lavas of other plume systems must result from an independent process, the most viable candidate at present remains core mantle interaction. While some plumes with high 3He/4He, such as Hawaii, appear to have been subjected to detectable addition of Os (and possibly He) from the outer core, others such as Iceland do not. A positive correlation between 187Os/188Os and 3He/4He from 9.6 to 19 Ra in Iceland picrites is best modeled as mixtures of 1 Ga or older ancient recycled crust mixed with primitive mantle or incompletely degassed depleted mantle isolated since 1 1.5 Ga, which preserves the high 3He/4He of the depleted mantle at the time. These mixtures create a hybrid source region that subsequently mixes with the present-day convecting MORB mantle during ascent and melting. This multistage mixing scenario requires convective isolation in the deep mantle for hundreds of million years or more to maintain these compositionally distinct hybrid sources. The 3He/4He of lavas derived from the Iceland plume changed over time, from a maximum of 50 Ra at 60 Ma, to approximately 25 27 Ra at present. The changes are coupled with distinct compositional gaps between the different aged lavas when 3He/4He is plotted versus various geochemical parameters such as 143Nd/144Nd and La/Sm. These relationships can be interpreted as an increase in the proportion of ancient recycled crust in the upwelling plume over this time period. The positive correlation between 187Os/188Os and 3He/4He demonstrates that the Iceland lava He isotopic compositions do not result from simple melt depletion histories and consequent removal of U and Th in their mantle sources. Instead their He isotopic compositions reflect mixtures of heterogeneous materials formed at different times with different U and Th concentrations. This hybridization is likely prevalent in all ocean island lavas derived from deep mantle sources.

No associations

LandOfFree

Say what you really think

Search LandOfFree.com for scientists and scientific papers. Rate them and share your experience with other people.

Rating

186Os and 187Os enrichments and high-3He/4He sources in the Earth’s mantle: Evidence from Icelandic picrites does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with 186Os and 187Os enrichments and high-3He/4He sources in the Earth’s mantle: Evidence from Icelandic picrites, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and 186Os and 187Os enrichments and high-3He/4He sources in the Earth’s mantle: Evidence from Icelandic picrites will most certainly appreciate the feedback.

Rate now

     

Profile ID: LFWR-SCP-O-965638

  Search
All data on this website is collected from public sources. Our data reflects the most accurate information available at the time of publication.