Beneath its rugged, rocky exterior, New England is wicked hot and on the move, a new study says.
Geophysicists at Yale and Rutgers have found a localized region of New England's upper mantle, centered beneath Vermont and New Hampshire, that is unusually hot and flowing upwards. The findings suggest that dynamic geologic processes are taking place beneath no-nonsense New England — despite the fact that the region has been tectonically quiet for millions of years.
The findings were published Nov. 29 in the online edition of the journal Geology.
"This is notable because it has been 200 million years since this region was located on a plate boundary and experienced a major plate tectonic event," said co-author Maureen Long, a Yale professor of geology and geophysics.
The warmer and dynamic mantle, also called a thermal upwelling, appears to have formed recently in geological terms, the researchers said, since there are no volcanic surface features in the region to indicate long-term activity. The researchers arrived at their findings by studying seismic waves from distant earthquakes, as the waves passed through New England.
The first author of the paper is Vadim Levin of Rutgers University. Additional co-authors are Peter Skryzalin and Yiran Li of Rutgers, and Ivette López of Yale, whose senior thesis research contributed to the study.
This is the result of the study.
Lateral changes in seismic velocity 100–300 km beneath the Appalachian orogen (eastern North America) do not follow the pattern of its major terranes, suggesting that more recent, and possibly ongoing, geodynamic processes are taking place in the sub-lithospheric mantle. One prominent, sharply delineated, seismically slow feature underlying parts of New England (USA) likely reflects a volume of significantly elevated temperatures in the asthenosphere. Using numerous new observations of splitting in seismic shear waves from distant earthquakes, we show that this upper mantle volume also lacks the systematic directional dependence (anisotropy) of seismic wave speed that is ubiquitous beneath most of northeastern North America. This regional anisotropic fabric, which likely forms as the asthenosphere is sheared by North American plate motion, appears to be locally erased beneath central New England, with changes in its strength occurring over distances on the order of 50 km. Highly localized variation in the strength of seismic anisotropy in a region of strongly elevated asthenospheric temperature suggests the presence of a narrow thermal upwelling in the upper mantle beneath New England. The lack of obvious surface expressions (volcanism or uplift) and the small lateral scale of the hypothesized upwelling suggest a geologically recent phenomenon.
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