Geochemistry of a new enriched mantle type locality in the northern hemisphere: Implications for the origin of the EM-I source

Details Geochemistry of a new enriched mantle type locality in the northern hemisphere: Implications for the origin of the EM-I source Geochemistry of a new enriched mantle type locality in the northern hemisphere: Implications for the origin of the EM-I source

Jan 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008e%26psl.265..167g&link_type=abstract

Earth and Planetary Science Letters, Volume 265, Issue 1-2, p. 167-182.

Computer Science

14

Scientific paper

Late Cretaceous (66.2 ± 0.5 Ma amphibole and 66.7 ± 0.2 Ma phlogopite 40Ar/39Ar ages) nephelinitic volcanic rocks from Godzilla Seamount in the eastern North Atlantic (34°N latitude) have trace element and Sr Nd Pb Hf-isotope compositions similar to the Enriched Mantle I (EM-I) endmember, except for their low 207Pb/204Pb relative to 206Pb/204Pb ratios (206Pb/204Pbin = 17.7, 207Pb/204Pbin = 15.34) plotting below the Northern Hemisphere Reference Line on the uranogenic Pb isotope diagram. O isotope data on amphibole separates are mantle-like (δ18O = 5.6 5.8‰). Age and location of the isolated Godzilla Seamount, however, preclude it from being derived from the Madeira or Canary hotspots, making a lower-mantle origin unlikely. Therefore we propose derivation from a shallow (lithospheric/asthenospheric) melting anomaly. As observed in mid-ocean-ridge and ocean-island basalts, there is a systematic decrease of 207Pb/204Pb ratios (and Δ7/4) in the individual EM-I endmember type localities towards northern latitudes with Godzilla lying on the extension of this trend. This trend is mirrored in ultra-potassic volcanic rocks such as lamproites and kimberlites, which reflect the composition of enriched subcontinental lithospheric mantle. Therefore, a global pattern in 207Pb/204Pb ratios and Δ7/4 is suggested. The geochemical composition of EM-I endmember type localities, including Godzilla lavas, and the enriched (DUPAL) anomaly in the southern hemisphere could reflect derivation from ancient, metasomatized subcontinental lithospheric mantle. We propose a two-stage model to explain the trace element and isotopic composition of the EM-I mantle endmember localities worldwide: 1) during the early history of the Earth, subcontinental lithosphere was metasomatized by melts from subducted slabs along convergent margins generating high μ (238U/204Pb) sources, and 2) as the Earth cooled, hydrous fluids replaced hydrous melts as the main slab component metasomatizing the subcontinental lithospheric mantle (generating EM-I sources with lower μ). In accordance with this model, the global variations in 207Pb/204Pb ratios and Δ7/4 could reflect geographic differences in μ and/or the age at which the transition from stages 1 to 2 took place in the Archaean lithosphere. The model would require a re-definition of the EM-I endmember to low 206Pb/204Pb, high 208Pb/204Pb (positive Δ8/4) but variable 207Pb/204Pb (positive and negative Δ7/4).

Affiliated with

Also associated with

No associations

Rating

Geochemistry of a new enriched mantle type locality in the northern hemisphere: Implications for the origin of the EM-I source 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 Geochemistry of a new enriched mantle type locality in the northern hemisphere: Implications for the origin of the EM-I source, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Geochemistry of a new enriched mantle type locality in the northern hemisphere: Implications for the origin of the EM-I source will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-753563