Regarding an Oceanic Crust/Upper Mantle Geochemical Signature at the KT Boundary: If not from Chicxulub Crater, then Where Did it Come from?

Evidence for a mantle and/or basaltic component in KT boundary distal ejecta is apparently inconsistent with ejection from Chicxulub Crater since it is located on ~35 km thick continental crust (DePaolo et al., 1983; Montanari et al., 1983; Hildebrand and Boynton, 1988, 1990). This evidence, along with ejected terrestrial chromites (Olds et al., 2016) suggest the impact sampled terrestrial mafic and/or ultramafic target rocks which are not known to exist in the Chicxulub target area. Possible resolutions to the paradox are: 1) the existence of an unmapped/unknown suture in Yucatan Platform basement, 2) an additional small unmapped/unknown impact site on oceanic lithosphere, or 3) an additional large impact on oceanic lithosphere or continental margin transitional to oceanic lithosphere. The third hypothesis is elaborated here since: 1) Ophiolites nearest to Chicxulub crater are found in Cuba and apparently were obducted in latest Cretaceous/earliest Danian times (García-Casco, 2008), inconsistent with the documented Eocene collision of Cuba with the Bahamas platform; and 2) Cuba hosts the world’s thickest known KT boundary deposits (Iturralde-Vinent, 1992; Kiyokawa et al., 2002; Tada et al., 2003). These and geometric considerations suggest oceanic crust and upper mantle rock, exposed as ophiolite in the Greater Antilles island chain, marks the rim of a roughly 700 km diameter impact basin deformed and dismembered from an originally circular form by at least 50 million years of left-lateral shear displacement along the North American-Caribbean transform plate boundary.