The Muertos margin (NE Caribbean): a review of the crustal structure and its tectonic significance

Abstract

Oblique convergence between the North American and Caribbean plates along the eastern Greater Antilles island arc (i.e., Hispaniola and Puerto Rico) has yielded a north-verging thrust system along the northern arc margin (i.e., forearc) and the south-verging thrust system along the southern arc margin (i.e., retroarc). Both thrust systems are associated along with elongated and deep bathymetric depressions; the Puerto Rico and Hispaniola trenches, and the Muertos trough. The north-eastern Caribbean is one of several oceanic island arcs around the world characterized by thrust belts developed on both arc margins. Some well-documented examples are Java-Timor, Panama and Vanuatu. A main structural feature is that the overall vergence of the retroarc thrust belt is opposite to that of the forearc thrust belt; resulting in a bi-vergent system. This bi-vergent geometry has been attributed to several processes, including: reversal of subduction polarity; subduction-driven mantle flow; stress transmission across the arc; gravitational spreading of the arc; and magmatic inflation within the arc. For several decades, the bi-vergent system of the north-eastern Caribbean has been attributed to reversal of subduction polarity, where the Caribbean plate’s interior is subducting north-eastwards beneath the island arc along the Muertos Trough, and the North American plate is subducting south-westwards along the Puerto Rico and Hispaniola trenches. The hypothesis of reversal subduction polarity is mainly based on the map-view and in depth distribution of seismicity in the north-eastern of the Caribbean plate. Although the existence of the subducting North American slab along the Puerto Rico-Hispaniola trenches is supported by a south-dipping Wadati-Benioff zone, the existence of subducting Caribbean slab along the Muertos Trough remains controversial. The occurrence of seismicity in the north-eastern Caribbean beneath the island arc is very diffuse making it difficult to assign event populations to outline the geometry of the respective subducted slab(s). In addition, knowledge of the crustal structure of Muertos margin had been limited until the last decade. From mid-70s the Muertos margin only had been partially explored using widely-spaced and low resolution 2D seismic reflection profiles and GLORIA large-range side-scan sonar data. Significant efforts were carried out from 2005 to 2013 to elucidate the crustal structure of the Muertos margin (i. e., Muertos thrust belt and Muertos trough). An international collaborative research, led by the Universidad Complutense of Madrid and the U.S. Geological Survey, carried out six geophysical cruises exploring the 650 km-long Muertos margin, from their western end in the Beata ridge to the eastern end in the Aves ridge. Cruises collected systematic high-resolution swath bathymetry, high-resolution seismic data, single- and multichannel seismic reflection profiles, wide-angle seismic transects and continuous gravity and magnetic data. The combined interpretation of new data and old reprocessed data have allowed a multi-scale approach to the study of the along- and across-strike crustal structure of the Muertos thrust belt and the adjoining Muertos trough. In addition, numerical and analogue modeling, constrained by the available data, have allowed to test different geodynamic scenarios for the Muertos margin. The results suggest the absence of a mantle-penetrating north-dipping Caribbean slab as expected in true subduction zones. This scenario implies that the Muertos margin is the result of a cross-arc transmission of the compressive stresses generated by the subduction of the North American plate at the Puerto Rico-Hispaniola trenches by means of a relatively rigid island arc. Therefore, the bi-vergent system in the north-eastern Caribbean plate can be primarily driven by a unidirectional subduction, not by a reversal of subduction polarity. Considering the Muertos margin as a retroarc compressive system, instead a subduction margin, has significant implications for the assessment on seismic hazard and natural resources in the north-eastern Caribbean.

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