A Revolution in Plate Tectonics?

Tomography reveals a low-wave-speed body beneath Yellowstone that does not extend deeper than ~ 200 km (Figure 3) [Christiansen et al., 2002]. At these depths, bodies greater than ~ 70 km in size horizontally, with anomalies stronger than ~ –1%, can be resolved. Beneath the ESRP a similar structure is detected, that is flanked by high-wave-speed bodies up to 200 km wide to the northwest and southeast. This is not what is predicted if the ESRP and flanking topographic swell represent a trailing plume head [Humphreys et al., 2000].

Whole-mantle tomography shows that Yellowstone lies at a profound lithospheric structural discontinuity where the Basin-& Range region to the southwest abuts the North American craton to the northeast. There is no significant low-wave-speed anomaly either in the lower mantle or the lower part of the upper mantle. In fact, wave-speeds are anomalously high in the lower half of the upper mantle.

The east-northeastward progression of late Neogene volcanic centers in the eastern Snake River Plain and Yellowstone region is an anchor for advocates of fixed plumes. Nevertheless, the thermal anomalies, as constrained by high-resolution tomography, are confined to the upper mantle (Humphreys et al., 2000). Plume proponents Waite et al. (2006) made a detailed tomographic study with local seismic arrays and also found no evidence for low velocities deeper than 400 km. A series of magmatic centers that progress west-northwestward into Oregon from the same origin during the same period, and that display a more regular time-distance progression, commonly is ignored by plume proponents because it does not “fit,” although plume advocate Jordan (2005) speculated that the aberrant trend formed by long-distance squirting from the fixed Yellowstone plume.

Why should that happen in any given tectonic model?

I suspect this supercontinent cycle is in need of a fresh paint job?

Much of the upper mantle is cooled from below, by bottomed out slabs, and cooled from within, by delaminating blobs. These blobs are colder than ambient mantle but hotter than slabs; they may contain most of the radioactivity of the upper mantle. They are constantly sinking and rising, delivering heat to the surface. The temperature of the surrounding mantle is buffered by the melting temperatures of the low-melting constituents as well as by the near-constant temperature of the lower continental crust. A partially molten asthenosphere, or one with partially molted blobs, cannot be treated as a homogeneous subsolidus ideal fluid; melting anomalies have other causes than high absolute temperature.

no more need to invoke comets as primary sources for earth's water!

...but only as an end member, chiefly to pin down what "tectonically dead" looks like.

Theory of Earth

Session ID#: 3924
Over the last 50 years, our understanding of the interior of Earth has advanced tremendously, yielding theories for its origin, evolution, internal structure, composition, and dynamics. Most powerful are interdisciplinary approaches that include physics, geophysics, energetics, thermodynamics, geochemistry, petrology, mineralogy, mantle dynamics, and volcanology. Nevertheless, persistent enigmas and paradoxes testify that major challenges still remain. We invite contributions that focus on interdisciplinary work to reveal the structure and dynamics of the interior of Earth, and links to surface manifestations. Observational, experimental and theoretical studies, along with historical reviews, are encouraged. We welcome in particular contributions that are provocative, radical, Devil’s Advocate, even outrageous, and have the potential to significantly advance our current understanding.

Co-Sponsor(s):
DI - Study of the Earth's Deep Interior
T - Tectonophysics
V - Volcanology, Geochemistry and Petrology

Index Terms:
8125 Evolution of the Earth [TECTONOPHYSICS]
8147 Planetary interiors [TECTONOPHYSICS]
8149 Planetary tectonics [TECTONOPHYSICS]
8180 Tomography [TECTONOPHYSICS]

Primary Convener: Don L Anderson, Caltech-Seismological Lab, Pasadena, CA, United States; Seismological Laboratory, Pasadena, CA, United States
Co-conveners: Jay Bass, University of Illinois at Urbana Champaign, Department of Geology, Urbana, IL, United States, Gillian R Foulger, University of Durham, Department of Earth Sciences, Durham, DH1, United Kingdom and James H Natland, University of Miami, Rosenstiel School of Marine and Atmospheric Science, Miami, FL, United States