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The Gulf of Mexico is a Jurassic backarc basin
Robert J. Stern
1
and
William R. Dickinson
2
1
Department of Geosciences, University of Texas at Dallas, 800 West Campbell Road, Richardson, Texas 75080, USA
2
Department of Geosciences, University of Arizona, Gould-Simpson Building #77, 1040 E 4th Street, Tucson, Arizona 85721, USA
Any basin with seafloor spreading that forms over an active
subduction zone is a backarc basin (BAB). The Gulf of Mexico
(GoM) opened behind the 232–150 Ma Nazas arc over an east-dipping
subduction zone in Late Jurassic time, beginning ca. 165 Ma,
and thus is a BAB. The hypothesis that the Gulf of Mexico formed
as a backarc basin explains two enigmas: (1) Why was the GoM
opening pole (79–84°W, 23–30°N) so different
from that of the central Atlantic (15–18°W, 65–67°N)?
and (2) Why was the GoM opening so short-lived (ca. 165–142
Ma), when there was no collision or other obvious reason for
seafloor spreading to stop? The GoM BAB hypothesis also illuminates
the relationship between the GoM and the Border rift system,
which can be traced from the GoM near the mouth of the Rio Grande
>2000 km along the U.S.–Mexico border into the Independence
Dike Swarm of eastern California. Late Jurassic rifting in the
Border rift system was succeeded by thermotectonic subsidence
through Early Cretaceous time. In addition, the segmentation
of the transitional crust beneath the northern GoM into a magmatically
robust segment beneath the Texas coast and a stretched margin
beneath Louisiana is also consistent with BAB behavior: igneous
activity is most prolific nearest the arc and diminishes with
distance from the trench. A possible objection to the GoM BAB
hypothesis is that the spreading ridge was oriented at high
angles to the Nazas arc trend, whereas modern oceanic BAB spreading
ridges generally parallel the associated arc. Continental BABs
like the GoM develop spreading ridge orientations that are often
at high angles to the associated convergent margin; for example,
spreading ridges associated with the Miocene Sea of Japan and
Andaman Sea BABs trend perpendicular to the associated arc.
Such geometries reflect the presence of extensional stresses
that are not orthogonal to the subduction zone, a situation
that also existed in the GoM region during Late Jurassic time.
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Copyright © 2011 by Geological Society of America