Back to Circum-Caribbean and North Andean tectonomagmatic evolution" Workshop

John Lewis¹, Pete Emmet², Paul Mann³, Michael Perfit⁴

¹ The George Washington University, Washington, D.C.
²Brazos Valley GeoServices, Inc., Cypress, Texas
³Institute of Geophysics, University of Texas at Austin, Texas
⁴University of Florida, Gainesville, Florida

We have integrated seismic reflection and refraction, marine and aero-magnetic, gravity and satellite remote sensing data with stratigraphic studies of wells and cores and geochemical/geochronological studies of igneous rocks from wells and dredge hauls to constrain the offshore boundaries of tectonic terranes over the Nicaraguan Rise (NR) and their projections onto adjacent land areas in Central America, Mexico and Belize. We recognize a Jurassic-Cretaceous rift fabric that trends ENE from onshore E. Honduras along the NR as defined by the 200 m isobath in Honduran waters. These rifts were partially-inverted in late Cretaceous and then reactivated in the Paleocene and E. Eocene as non-marine extensional basins that were inverted again in the M. Eocene. Continental crust may underlie the NR where an earlier Mesozoic rift fabric can be inferred by the presence of U. Jurassic (?) to L. Cretaceous syn-rift clastics overlain by a L. Cretaceous carbonate platform. Igneous intrusions and extrusive flows are intercalated with Cretaceous and Eocene strata penetrated by numerous wells along the NR eastward to Jamaica and southward into Nicaraguan waters. The location and nature of the transition from continental to arc crust along the NR is not known. Nd-Sr and Pb isotope ratios of arc-related calc-alkaline granitoids and volcanic rocks from the W. part of the Cayman Ridge indicate that these rocks were intruded into continental crust. This confirms that crustal rocks of the W. Cayman Ridge are the rifted eastern extension of the continental Maya block of Belize, Mexico and Guatemala, as has been suggested previously. The compositions of the W. Cayman granitoids differ significantly from those of the Sierra Maestra, forming the easternmost part of the Cayman Ridge, and from other granitoids in the Greater Antilles and the NR, including Jamaica. The W. Cayman granitoid magmatism (66-62 Ma) is slightly older than that of the Sierra Maestra (60-47 Ma) but overlaps in age the Above Rocks in Jamaica, the Terre Neuve in Haiti, and plutons of the NR and N. Honduras. These data indicate the probability of three different, partly coeval, subduction-related magma systems in the NW Caribbean over the area of the NR during the interval 66 to 47 Ma. Northward (oblique?) subduction of the Siuna terrane along the Honduras-Nicaragua border and northern NR is suggested for the granitoid magmatism onshore N. Honduras and offshore along the NR. Our studies place new constraints on models for the tectonic/magmatic evolution of the area.