The orthodox, geophysics-based, plate tectonic model for the evolution of the Caribbean has the Cayman Trough closed at the beginning of the Eocene and the Chortis block lying next to the southwest coast of Mexico. This model may as such be tested geologically, because the Mexican basement contains the north-south trending Grenvillian Oaxaca complex which is abruptly truncated at the coast. Its continuation ought, therefore, to lie within Chortis. To this end the Grenville was searched for in Honduras and found. It extends from the east wall of the Sula Valley above the town of El Progresso eastwards as far as the Valle de Yoro, a distance of 60km. Its north-south exposure is probably no more than 10km, for on the north it is bounded by phylites and on the south is covered by Mesozoic sediments. Massive, sometimes banded, quartzofelspathic rocks dominate the metamorphic sequence. Minor pelitic units contain layers of chlorite+biotite and biotite+garnet reminiscent of the chlorite-biotite-almandine zones of the Dalradian and indicate attainment of the greenschist-amphibolite facies boundary. Granites intruding the metamorphic rocks are strongly lineated and contain zircon concordant at 1.0Ga, while their Sm-Nd systematics indicate mantle separation ages of 1.4Ga. A translation of 1000km is required to bring the two Grenvillian basements into juxtaposition. Although this figure is 5 to 10 percent less than the 1050 to 1100km of extension produced by the opening of the Cayman Trough (Perfitt and Barrett, in The Geology of North America, v.H, GSA, 1990) it cannot be denied that the Grenville of Honduras lies almost exactly where geophysics predicts it to be, and it is to be hoped that its discovery will help answer what has been said to be one of the most bitterly contested questions in Caribbean geology, namely the amount of strike-slip motion along the Motagua-Polochic fault system.

In: Manton, W.I., 1996, The Grenville Of Honduras, Geological Society of America, Annual Meeting, Program with Abstracts, p. A-493.

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