238U-230Th constraints on mantle upwelling and plume-ridge interaction along the Reykjanes Ridge

Details 238U-230Th constraints on mantle upwelling and plume-ridge interaction along the Reykjanes Ridge 238U-230Th constraints on mantle upwelling and plume-ridge interaction along the Reykjanes Ridge

May 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001e%26psl.187..259p&link_type=abstract

Earth and Planetary Science Letters, Volume 187, Issue 3-4, p. 259-272.

Computer Science

14

Scientific paper

238U-230Th-226Ra disequilibria data are presented for dredged glasses from the slow-spreading, plume-influenced Reykjanes Ridge, and lavas from the Reykjanes Peninsula, Iceland. Southern Reykjanes Ridge samples (57.7°-58.8°N), identified as `zero-age' (i.e. <8 ka) from measured 226Ra-230Th disequilibrium, lie on a shallow trend on the (230Th/232Th) vs. (238U/232Th) equiline diagram. Within this 150 km ridge section, samples north of the weak segment boundary at 58.42°N have lower U/Th, higher Th contents and higher (230Th/238U) than those to the south. This local compositional control on the degree of 230Th-238U disequilibrium is inferred to result from variable mixing between melts from `enriched' and `depleted' components in the upwelling mantle. This is supported by a northward increase in 206Pb/204Pb and He isotope ratios within this region. A sample from the northern, shallow part of the Reykjanes Ridge (61.93°N) also lies within this trend, with relatively high U/Th. In contrast, post-glacial lavas on the Reykjanes Peninsula show broadly similar U/Th to the Reykjanes Ridge samples, but at significantly lower (230Th/232Th) (~1.15 vs. ~1.30). This distinction is most likely due to a difference in mantle upwelling rate - a high upwelling rate associated with the mantle plume beneath Iceland will give rise to lower 230Th-238U disequilibrium for a particular U/Th value due to the reduced opportunity for 230Th in-growth in the melt column - although differences in initial melt productivity might also play a role. Active upwelling associated with the Iceland plume probably does not extend far along the Reykjanes Ridge.

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