The Padre Miguel Ignimbrite Suite, central Honduras: Paleomagnetism, geochronology, and tectonic implications

Abstract

The Padre Miguel Group in western Honduras is a silicic volcanic sequence that forms part of the Central American Miocene volcanic arc built on the Chortis continental fragment. We report new 40Ar/39Ar data of 16.1±0.2Ma and 14.42±0.08Ma for the Padre Miguel Group, and present paleomagnetic data for 36 cooling units (mainly ignimbrites) from localities north and northeast of the capital city of Tegucigalpa. These rocks are characterized by univectorial characteristic magnetization carried mainly by low-Ti titanomagnetites, or two component magnetizations with a minor secondary overprint. Dual polarity magnetizations suggest that it is a primary thermo-remanence and the obtained data scatter can be straightforwardly explained by paleosecular variation. The overall mean of 33 selected sites (14.39°N, 87.14°W) defines a paleomagnetic pole at lat=80.0°N, lon=142.9°E (K=24.5, A95=5.2°). The overall mean compared with the North America expected direction indicates statistically insignificant rotation and inclination anomaly (R=−4.1°±6.1° and an F=−8.6°±11.3°). Restoring 255km of sinistral slip in the Polochic–Motagua fault system, as suggested by Cayman Trough reconstructions since 15Ma, brings the mid-Miocene arcs of southern Mexico (Oaxaca) and the Central America ignimbrite province into alignment; this is consistent with a derivation of the Chortis Block from southern Mexico. Our paleomagnetic and geochronological studies hence support models that explain the offset of the Miocene ignimbrite belt of Central America by post-Middle Miocene displacement of the Chortis Block relative to North America.