Transcript Seismic, Well, and Gravity Constraints on the Structure and

The Nature of the Crust Beneath the Deep Gulf of Mexico and Development of the
Syn-Rift and Early Post-Rift Gulf Basin
Dennis L. Harry, Geosciences, Colorado State University, Colorado State University, Department of
Geosciences, Fort Collins, CO 80523-1482
Ordovician
Mesozoic opening of the Gulf of Mexico was strongly
influenced by pre-existing tectonic structures associated with
assembly of Pangea during the Paleozoic Era. The figure at right
illustrates the key sequence of events. From top to bottom,
formation of the Wiggins volcanic arc by south-directed
subduction; collision of the Wiggins arc with North America,
forming the Ouachita suture with a transition to north-directed
subduction further south; final suturing of Gondwana with
Laurentia, creating an orogen underlain by shallow mantle;
Triassic rifting south of the Ouachita orogen.
Key findings to date are derived from finite element modeling
and are schematically illustrated in the figure:
 The interaction of inherited crust and mantle weaknesses
exerted a primary control on the locus of extension and shifts in
depocenters in the rift. The shallow mantle beneath the Ouachita
orogen served as a strong zone, forcing extension to occur in
regions further southward.
 Early extension of the Wiggins terrain formed the Interior Salt
Basin, but the suture between South America and the Wiggins arc
proved weaker in the long run, causing extension to shift further
south to form the modern Gulf of Mexico.
 The model predicts very little rift-related magmatism,
consistent with observations on the Gulf continental margins.
 By comparison with International Ocean Drilling Program
results on the non-volcanic Iberia margin, the model raises the
question of whether the deep water central Gulf region might not
be underlain by oceanic crust, and may instead potentially contain
syn-rift hydrocarbon source rocks.
North
America
Ouachita
Trough
Wiggins
Arc
South
America
Mississippi (early Ouachita orogeny)
Ouachita
Suture
Pennsylvanian (late Ouachita orogeny)
Black Warrior
Basin
Alleghanian
Suture
Triassic (rifting)
Ouachita
Orogen
Salt Basin
Wiggins Gulf of
Arch Mexico
South
America