An aeromagnetic survey of Honduras and its northeastern Caribbean coastal area covering a continuous area of 137,400 km2 was acquired by the Honduran government in 1985 and provided to the University of Texas at Austin for research purposes in 2002. We correlate regional and continuous aeromagnetic features with a compilation of geologic data to reveal the extent, structural grain, and inferred boundaries of tectonic terranes that compose the remote and understudied, Precambrian-Paleozoic continental Chortis block of Honduras. A regional geologic map and a compilation of isotopic age dates and lead isotope data are used in conjunction with and geo-referenced to the aero-magnetic map. These combined data provide a basis for subdividing the 531,370 km2 Chortis block into three tectonic terranes with distinctive aeromagnetic expression, lithologies, structural styles, metamorphic grade, isotopically and paleontologically determined ages, and lead isotope values: (1) The Central Chortis terrane occupies an area of 110,600 km2, exhibits a belt of roughly east-west–trending high magnetic values, and exposes small, discontinuous outcrops of Grenville to Paleozoic continental metamorphic rocks including greenschist to amphibolite grade phyllite, schist, gneiss, and orthogneiss that have been previously dated in the range of 1 Ga to 222 Ma; the northern 59,990 km2 margin of the Central Chortis terrane along the northern Caribbean coast of Honduras exhibits an irregular pattern of east-west–trending magnetic highs and lows that correlates with an east-west–trending belt of early Paleozoic to Tertiary age metamorphic rocks intruded by Late Cretaceous and early Cenozoic plutons in the range of 93.3–28.9 Ma. (2) The Eastern Chortis terrane occupies an area of 185,560 km2, exhibits belts of roughly northeast-trending high magnetic values, and correlates with outcrops of folded and thrusted Jurassic metasedimentary phyllites and schists forming a greenschist-grade basement; we propose that the Eastern and Central terranes are distinct terranes based on the strong differences in their structural style and aeromagnetic grain, sedimentary thickness, metamorphic grade, and lead isotope values. (3) The Southern Chortis terrane occupies an area of 120,100 km2, contains one known basement outcrop of metaigneous rock, exhibits a uniformly low magnetic intensity that contrasts with the rest of the Chortis block, and is associated with an extensive area of Miocene pyroclastic strata deposited adjacent to the late Cenozoic Central American volcanic arc. The outlines of the terranes as constrained by the aeromagnetic, lithologic, age, and lead isotope data are restored to their pre–early Eocene position along the southwestern coast of Mexico by a 40° clockwise rotation and 1100 km of documented post–early Eocene (ca. 43 Ma) left-lateral offset along the strike-slip faults of the northern Caribbean strike-slip plate boundary. The inner continental and outboard oceanic terranes of Chortis and the 120,100 km2 Siuna terrane to the south trend roughly north-south and align with terranes of similar magnetic trend, lithology, age, and crustal character in southwestern Mexico. Additional progress in mapping and isotopic dating is needed for the proposed Chortis terranes in Honduras in order to constrain this proposed position against much better mapped and dated rocks in southwestern Mexico.
