[Taxacom] Croizat got it right again, again

John Grehan calabar.john at gmail.com
Thu Aug 13 12:35:21 CDT 2020

I appreciate that one can choose or not to favor the origin of modern life
by chance processes of exceptional dispersal and view the modern
distributions as disconnected from earth history. Everyone, myself
included, is free to believe what they want to believe. But science is not
about belief. What scholars of science generally recognize as an important
criterion for the efficacy of a scientific approach is its ability to
predict new phenomena - before they are empirically discovered. In this
respect Croizat has been quite successful.

Another marker in this success concerns the eastern Pacific where Croizat
(1958) predicted the former existence of island clusters of galaxies of
islands that have since been lost. When he wrote this it was before
knowledge of modern plate tectonics so he probably thought of the loss more
in terms of subsidence than tectonic transport. Regardless, it is the
former existence of such 'islands' that he predicted and this has been
recently corroborated through tectonic research that now provides empirical
evidence for major island arcs the size of micro-continents in the eastern
Pacific, slab remnants now located beneath the American continents as the
arcs were swallowed up. The slabs provide evidence that the island arcs
were stable and long-term existence over millions of years. Half of Mexico
is made up of one of these arcs.

Abstract and title below. Open access:

Clennett, E. J., Sigloch, K., Mihalynuk, M. G., Seton, M., Henderson, M.
A.,  Hosseini, K., et al. (2020). A quantitative tomotectonic
plate reconstruction of western North America and the eastern Pacific
basin. Geochemistry, Geophysics, Geosystems, 20, e2020GC009117.
https://doi.org/  10.1029/2020GC009117

Abstract Plate reconstructions since the breakup of Pangaea are mostly
based on the preserved spreading history of ocean basins, within absolute
reference frames that are constrained by a combination of age‐progressive
hotspot tracks and paleomagnetic data. The evolution of destructive plate
margins is difficult to constrain from surface observations as much of the
evidence has been subducted. Seismic tomography can directly constrain
paleotrench locations by imaging subducted lithosphere in the mantle. This
new evidence, combined with the geological surface record of subduction,
suggests that several intraoceanic arcs existed between the Farallon Ocean
and North America during late Mesozoic times—in contrast to
existing quantitative models that typically show long‐lived subduction of
the Farallon plate beneath the continental margin. We present a
continuously closing plate model for the eastern Pacific basin from 170
Ma to present, constrained using “tomotectonic analysis”—the integration of
surface and subsurface data. During the Middle to Late Jurassic, we show
simultaneous eastward and westward subduction of oceanic plates under an
archipelago composed of Cordilleran arc terranes. As North America drifts
westward, it diachronously overrides the archipelago and its arcs,
beginning in the latest Jurassic. During and postaccretion, Cordilleran
terranes are translated thousands of kilometers along the continental
margin, as constrained by paleomagnetic evidence. Final accretions to North
America occur during the Eocene, ending ~100 Myr of archipelago override.
This model provides a detailed, quantitative tectonic history for the
eastern Pacific domain, paving the way for tomotectonic analysis to be used
in other paleo‐oceanic regions.

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