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Figure 1. Tectonic map of the southern U.S. continental margin. Northern boundary of the Gulf of Mexico basin is rep-
resented by the Cretaceous shelf edge, adapted from Harry and Londono (2004). Locations of the GUMBO lines and the
limit of oceanic crust in the Gulf of Mexico are from Christeson et al. (2014). Location of basinward salt limit is from
Hudec et al. (2013). Louann salt province in the Gulf of Mexico, denoted by gray shading, is from Diegel et al. (1995).
Locations of the Precambrian rift-transform margin, and other geologic structures and terranes, were derived from
Thomas (1991, 2011). MU—Monroe Uplift; BU—Benton Uplift; BBU—Broken Bow Uplift; LU—Luling Uplift; WU—Waco
Uplift; SMA—San Marcos Arch. L1 (onshore extension of GUMBO 1), L2, and L3 (onshore extension of GUMBO 3) are
locations of cross-sectional profiles examined in Figures 4 and DR2 [see text footnote 1]. AL—Alabama; AR—Arkansas;
LA—Louisiana; FL—Florida; GA—Georgia; KY—Kentucky; MO—Missouri; MS—Mississippi; NC—North Carolina; OK—
Oklahoma; SC—South Carolina; TN—Tennessee; TX—Texas; VA—Virginia; WV—West Virginia.

2. The Grenville orogeny was followed by a associated with basement highs, such details of its evolutionary history remain
Neoproterozoic rifting episode that as the Sabine and Monroe uplifts in unresolved. These include, but are not lim-
resulted in the breakup of Rodinia and Louisiana and the Wiggins Arch in ited to, the geometry of the Precambrian
the subsequent opening of the Iapetus Alabama and Mississippi. rift-transform margin, depth and spatial
Ocean. The resulting passive margin, 4. Finally, Late Triassic rifting episodes, extent of the allochthonous terranes that
outlining the southeastern continental during the breakup of Pangaea, led to participated in the Ouachita orogeny, and
margin of Laurentia, is widely thought to the opening of the Atlantic Ocean and variations in continental stretching and
be composed of a series of rift and trans- the Gulf of Mexico (Dickinson, 2009; magmatic activity across the northern Gulf
form segments (Hatcher et al., 1989; Thomas, 2011; Huerta and Harry, 2012). of Mexico during Mesozoic rifting.
Thomas, 1991, 2011). Continental extension, followed by mid-
3. The closing of the Iapetus Ocean and Jurassic seafloor spreading, produced VELOCITY MODELS
the consequent assembly of the Pangaea the current configuration of an arcuate The following eight models are com-
supercontinent during the late wedge of oceanic crust beneath the deep pared in this study: DNA13 (Porritt et al.,
Paleozoic included a collision between Gulf of Mexico surrounded by transi- 2014); PLH15 (Porter et al., 2016); PM15
Laurentia, Gondwana, and enclosed tional continental crust of variable width (Pollitz and Mooney, 2016); SR16 (Shen
island arcs, which resulted in the (Christeson et al., 2014). and Ritzwoller, 2016); SLK15 (Schmandt
Ouachita orogeny. Contemporaneous Although there is general agreement on et al., 2015); NA07 (Bedle and van der Lee,
terranes that participated in the the sequence of tectonic events that formed 2009); SL14 (Schmandt and Lin, 2014); and
Ouachita orogeny, the composition and the present-day crustal structure of the YFCR14 (Yuan et al., 2014). Our compari-
origin of which are widely debated, are southern U.S. continental margin, several son is limited to shear wave velocity (Vs)

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