Other
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmdi24a..07c&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #DI24A-07
Other
1025 Composition Of The Mantle, 1038 Mantle Processes (3621), 1040 Radiogenic Isotope Geochemistry, 1065 Major And Trace Element Geochemistry
Scientific paper
Helium is a unique tracer for the geodynamic evolution of the Earth. It does not get recycled back into the mantle like other incompatible elements but rather gets degassed to the atmosphere during crust formation and subduction and then is lost to space. Thus, the presence of primordial 3He in the Earth poses fundamental questions: How does Earth retain primordial helium during accretion and catastrophic moon formation? Where is primordial helium preserved during subsequent whole mantle convection, and continuous degassing through magma generation. How are 3He/4He up to 50Ra in plume-related basalts explained when continuous production of 4He from Th+U decay reduces the 3He/4He ratio of the Earth? The last few years have seen an explosion of new ideas to address these questions. Three are highlighted here. (1) Through whole mantle convection, the mantle that has been degassed through ocean and continental crust formation remixes with yet undegassed portions of the mantle, resulting in preservation of high 3He/4He in the depleted mantle (Class & Goldstein 2005, Nature 436, 1107-1112). (2) Helium diffused early in Earth history into refractory harzburgite melt residues, where it is preserved and later sampled during melting (Albarède 2008, Science 319, 943-945). (3) Excesses of Ti correlate positively with 3He/4He, possibly suggesting association of ancient slabs composed of refractory eclogite with high 3He/4He peridotite (Jackson et al. 2008, G3 9, Q04027). Here we show that these seemingly contradictory interpretations merge into a hybrid helium evolution model. Including early Iceland plume and Samoa data, the global correlation between helium isotope ratios and Th persists, pointing towards a depleted composition for the high 3He/4He endmember, where a correlation with Ti excess is superimposed. For a given Th content ocean island basalts vary in helium isotope ratios from mid-ocean ridge like helium towards higher or lower values, but not both, emphasizing the fundamental significance of mid-ocean ridge-type helium. This requires stratification of the helium isotope ratios in the mantle with depth, caused either by age or variable mixing efficiency. The relationship to Ti excess can be ascribed to the slab graveyard at the core-mantle boundary forming the hot core of plumes, which are most likely to sample the high 3He/4He but incompatible element depleted lithologies of the deep mantle.
Class Cornelia
Goldstein Steven L.
No associations
LandOfFree
Helium and Other Geochemical Evidence on the Mantle Composition Above the Core- Mantle Boundary 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 Helium and Other Geochemical Evidence on the Mantle Composition Above the Core- Mantle Boundary, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Helium and Other Geochemical Evidence on the Mantle Composition Above the Core- Mantle Boundary will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1241692