Middle America – Intracontinental extension along ancient structures

Abstract

Middle America manifests a regional tectonic fabric that results from Triassic - Recent reactivation of older structures. N60oW transform motion, parallel to major fractures and faults of the western Central Atlantic and eastern North America, accommodated Gulf of Mexico – Caribbean opening. Rifting occurred along N35oE tectonic lineaments, reversing Palaeozoic (Appalachian/Caledonian) convergence. Crustal thicknesses decline away from cratons. Seismic data from the Gulf of Mexico reveal salt-bearing rifts bounded by basement highs, basinward thinning of continental crust, outboard seaward-dipping wedges and thin (?oceanic) crust, repeating the geology offshore eastern N America and the extended margins of the N and S Atlantic. The Caribbean interior shows the same architecture, here capped by Upper Cretaceous basalts (seismic Horizon B.), similar to flows above extended crust offshore Norway and NW UK. Change of B. character from smooth (subaerial) to rough (subaqueous) occurs above a major, wedge-bounding fault with indications of shelf edge buildup. Diapiric piercing and tilting/uplift of this singular horizon recall salt rafting of igneous layers in Louisiana. Pre-B" seismic architecture indicates rift to carbonate platform, wedges of seaward-dipping reflectors and thinned crust above shallow Moho. Thick (10 km) layers of continental velocities below Central America and the Lesser Antilles accord with .extreme continental-like. high silica chemistry of volcanic rocks. They are dispersed continental fragments, similar to those revealed in recent years by velocity data and ancient inherited zircons in the Izu-Bonin, East Java, Luzon, Solomon and Vanuatu arcs. Lesser Antilles xenoliths include granite, calcareous metasediment, gypsum and rounded quartz grains. Eocene ash fall zircons on Barbados record Antillean volcanism; admixed Palaeozoic/Proterozoic zircons record ancient arc roots. The Antillean continental velocity layer extends to Barbados. Here, seismic and oil data relate the Eocene Barbados Scotland to the fluvial/deltaic Misoa and the underlying La Luna source of the Maracaibo Basin. The Scotland carries orogenic and cratonal detritus, mudcracks and freshwater molluscs, indicating a local, continental origin. Inherited zircons from Cuba, Hispaniola, NW Venezuela, Margarita, Trinidad, Granada and Carriacou indicate autochthonous, ancient crustal foundations. Radical rethink of Yucat.n - Caribbean basin palaeogeography is indicated. Located between the Gulf of Mexico and northern South America they probably carry hydrocarbon potential.

AAPG Datapages/Search and Discovery Article #90330©2018 AAPG Hedberg: Geology of Middle America – the Gulf of Mexico, Yucatan, Caribbean, Grenada and Tobago Basins and Their Margins “Integration of the geology of the area from the southern onshore of North America to the northern onshore of South America”, Siguenza, Guadalajara, Spain, July 2-5, 2018