Mathematics – Logic
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm...v41a11i&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #V41A-11
Mathematics
Logic
8115 Core Processes (1507), 8450 Planetary Volcanism (5480)
Scientific paper
Rocks unusually rich in Mg erupt from particularly hot mantle sources, consistent with mantle plumes. We compile a record of the ages of high-Mg igneous rocks, including komatiites and picrites, spanning 3.8 billion years of Earth history. We produce a time-series from this record that presumably reflects mantle plume events. Spectral energies in this record are concentrated at periods of approximately 273 My and 34 My. These periods are analogous to the length of the cosmic year and the frequency of cometary and meteorite impacts, respectively. Therefore we infer that mantle plume volcanism responds to an exogenic process. However, others have suggested that resonance between free core nutations and those forced by luni-solar torques drives mantle plumes (Williams 1994; Greff-Lefftz and Legros 1999). It is not possible at the present time to complete viable spectral analysis of a time-series of resonant core nutations, because the timing of resonant events are associated with a huge uncertainty (+/- 100 My or more). Admittedly, there is an interesting similarity between the numbers of predicted resonant events and the numbers of mantle plume events through Earth history. Further, this hypothesis is compatible with a lull in mantle plume volcanism between about 1750 and 1250 Ma, which may not be consistent with a cometary impact model. (Very few impact events have been found for this time period, but the record is still very sparse.) If we use the plume time-series to "tune" the record of resonant nutations, then we conclude that the Earth's deceleration rate has varied considerably through geologic time. Particularly significant solar torques may have been associated with mantle plume events for which there are no known cometary impacts. Further tests of this model require that the Earth's deceleration rate through time be better constained. Until this is accomplished, we continue to advocate an exogenic drive to mantle plume volcanism.
Abbott Dallas H.
Isley Ann E.
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