WHERE ARE THE OPHIOLITES OF THE OUACHITA COLLISIONAL FOLD-THRUST BELT?

The Ouachita fold-thrust belt in Oklahoma and Arkansas formed during the Pennsylvanian Ouachita Orogeny due to the collision of a southern continent and southern margin of North America. The tectonic models (e.g., Houseknecht, 1983) of the Ouachita fold-thrust belt involve the presence of an accretionary prism and volcanic arc associated with a south dipping subduction zone. There are two lines of evidence for the presence of the volcanic arc. They are the presence of 1) Mississippian volcanic rocks in the subsurface along the flanks of the Sabine uplift to the south of the Ouachita Mountains  (Houseknecht, 1983), and 2) volcaniclastic rocks on the surface and in the subsurface in the Mississippian Stanley Formation in Arkansas.  The tectonic models suggest that the accretionary prism developed over the oceanic crust and therefore should contain ophiolites as pieces of oceanic crust and/or supra-subduction ophiolites.  However, no ophiolites has been reported on the surface or in the subsurface along the entire Ouachita fold-thrust belt from the Benton-Broken Bow uplift in the hinterland area of the belt to the Arkoma Foreland basin to the north. Ophiolites are, however,  present in all other collisional fold thrust belts such as the Appalachians, Caledonians, Alps, Himalayas, and Zagros fold-thrust belts.

Ophiolites of the Ouachita fold-thrust belt may be present below the Mesozoic sediments to the south of the Benton- Broken Bow uplift area. However, before an exploration well is drilled in this area a high resolution gravity survey is needed to determine if there are structural high areas that may have a continental crust density signature. If these areas exist, the well may be drilled to test if the "Ouachita Ophioites" are present in the subsurface in the area from the south of the Benton-Broken Bow uplift to the north of the Sabine uplift. The gravity survey may also provide clues on the geometry of the buried accretionary prism. Eventually, a deep reflection seismic profile from the Arkoma Basin to the Sabine uplift will be needed to determine the geometry of the structural features related to Ouachita fold-thrust belt, including the Woodford detachment surface which is well observed in the reflection seismic profiles in the Arkoma Foreland basin.