Implications for Long-Term Mantle History of the Restricted Distribution of Large Igneous Province (LIP) Plume Sources at the Core-Mantle Boundary (CMB)

Details Implications for Long-Term Mantle History of the Restricted Distribution of Large Igneous Province (LIP) Plume Sources at the Core-Mantle Boundary (CMB) Implications for Long-Term Mantle History of the Restricted Distribution of Large Igneous Province (LIP) Plume Sources at the Core-Mantle Boundary (CMB)

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmdi44a..07b&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #DI44A-07

Physics

6982 Tomography And Imaging (7270, 8180), 7208 Mantle (1212, 1213, 8124), 8124 Earth'S Interior: Composition And State (1212, 7207, 7208, 8105), 8137 Hotspots, Large Igneous Provinces, And Flood Basalt Volcanism, 8157 Plate Motions: Past (3040)

Scientific paper

We have found, by rotation of LIPs of the past 300 My to their eruption sites in a paleomagnetic reference frame corrected for true polar wander, that those sites concentrate vertically above the margins at the CMB of the two Large Low Shear Wave Velocity Provinces(LLSVPs) of the deep mantle (Torsvik et al. 2006). This surprising discovery of narrow (< 200 wide) Plume Generation Zones stable for at least 300 My on the CMB at the LLSVP margins is consistent with the idea that the LLSVPs are compositionally (and probably also thermally) distinct dense bodies (each making up ca. 1 percent of mantle mass) rather than thermally buoyant "superplumes". The "centers of mass" of the two LLSVPs are antipodally disposed close to the equator, an intriguing possible further indication of long-term stability because the positively elevated part of the residual geoid, which matches the LLSVPs and therefore also appears also to have been stable for at least 300 My finds an analog in the aeroid of Mars of which the elevated regions are themselves antipodal on the equator. Because some volcanoes of Mars perhaps > 3.8 My in age are concentrated on the rims of the elevated aeroid it is worth considering the implications of the possible isolation of the LLSVPs from the rest of the mantle through most of Earth history. If the 2 percent of mantle mass that makes the LLSVPs has escaped being involved in making ocean floor it will be more Fe rich and denser than the average mantle. If it has also escaped being involved in making continent it will be richer in U,Th and K and hotter. It will have distinctive noble gas concentrations and could be the source (by diffusion) of the Earth's current 3He flux (Burke et al. 2008). If a velocity change attributable to a perovskite/post-perovskite transition can be mapped consistently both within and outside the LLSVPs it will help in testing the idea that the interiors of LLSVPs are hotter than the rest of the deep mantle.

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