South-Central Section - 49th Annual Meeting (19–20 March 2015)

Paper No. 8
Presentation Time: 10:45 AM


EWING, Thomas E., Bureau of Economic Geology, University of Texas at Austin, 10100 Burnet Rd, Austin, TX 78758,

Stern and Dickinson proposed that the Gulf of Mexico is a back-arc basin. But this faces strong geometric and timing concerns. Gulf extension begins in the Late Triassic and proceeds to crustal necking and hyperextended crust (or exhumed mantle) by late middle Jurassic. Known backarc basin deposits in southwestern North America, by contrast, only begin in late Jurassic.

GOM formation can be modeled as a two-stage process. In Phase I (Norian-Callovian, 205-162 Ma), extension occurred on NW-SE axes as part of Tethyan opening and ejection of Laurentia from Pangea. NW-trending linears are abundant in Mexico, present in the Florida-Alabama-Arkansas axis, and probably present within the basin as well. Small blocks of full-thickness lithosphere pulled off, separated by zones of highly extended continent (as Sabine block vs East Texas basin). Cordilleran arc influence was restricted, but might account for strike changes in grabens and other features.

After salt deposition ended (Oxfordian, about 162 Ma), ocean crust initiated along the 'seam' of hyperextended crust beginning Phase II. At that time, rates of magma production vastly increased at the west end of the seam (2-3x). This is likely due to incipient back-arc mantle upwelling behind the Nazas arc. High rates of ocean crust injection coupled with a Yucatan block that was 'free-floating' to rotate that block counterclockwise some 42 degrees.

Phase II ended about 140 Ma (Barremian?). Was this due to termination of backarc mantle upwelling? Or did Yucatan run into something that restrained the rotation?

  • GOM_Talk_GSA.pptx (32.0 MB)