Petrologic and Tectonic Significance of Mesozoic Volcanic Rocks Exposed Along the Río Wampú, Eastern Honduras

T J Weiland (Geology Dept., Georgia Southwestern College, Americus, GA 31709; 912-928-1613)

I B Suayah (P.O Box #452, Chapel Hill, NC 27514-0452)

R C Finch (Dept. of Earth Sciences, Tennessee Technological Univ., Box 5062, Cookeville, TN 38505)

A thick sequence of dark-red lava flows and clastic rocks with abundant volcanic debris crops out along the Río Wampú of eastern Honduras. Based on the lithologic characteristics of these rocks, field interpretations of the Río Wampú stratigraphy, and K-Ar determinations on volcanic samples, these redbeds and associated volcanic units are tentatively correlated with the Late Cretaceous Valle de Angeles Group of Central Honduras. It appears that these strata unconformably overlie the Jurassic Agua Fría Formation of the Honduras Group.

The lava samples are predominantly microporphyritic andesites and basaltic andesites. Immobile-element concentrations in both clinopyroxenes and whole rock indicate a high-K tholeiitic classification. Elevated TiO2 concentrations in the basaltic andesites apparently reflect a primary characteristic of uncertain origin. Based on rare-earth and trace-element concentrations, these rocks probably represent partial mantle melts which were modified by substantial fractionation of modal phases.

The presence of widespread Mesozoic redbeds and associated volcanics in Honduras was previously used as evidence of regional extensional tectonics. In contrast, structural, geochemical and stratigraphic data collected during this study suggest that the Río Wampú volcanic rocks and associated redbeds were formed during a compressional subduction-related event on the Chortis block. Similar high-TiO2 basaltic andesites and andesites are reported along several modern active continental margins.

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