Geology of the Zambrano Quadrangle, Honduras, Central America
The Matagalpa Formation, the oldest unit exposed (Oligocene? - Early Miocene?), consists of over 300 meters of hydrothermally altered mafic flows and some interbedded sedimentary rocks. Up to 1400 meters of siliceous volcanic and sedimentary rocks (Mid-Miocene-Pliocene?), correlative with the Padre Miguel Group in Guatemala, nonconformably overlie the Matagalpa Formation. The lower 1000 meters of this group consists mainly of rhyolitic to andesitic ignimbrites that were probably erupted from a vertically zoned magma. Faulting accompanied the extrusion of these ignimbrites. These are overlain by up to 400 meters of airfall tuffs, fluvial, lacustrine, and laharic deposits, and a series of structurally-controlled rhyolitic domes. The uppermost unit consists of several thin ignimbrites. Most of the faulting occurred after the deposition of the Padre Miguel Group, probably from Middle Pliocene to Early Pleistocene times. Normal faults trend N50-80°W, N10-25°E, N35°E, and N70°E. They are probably surficial features caused by left-lateral shear in the basement related to movement between the Caribbean and Americas plates. Minor northwest-trending folds formed contemporaneous with and perhaps prior to faulting. Olivine basalt was extruded from structurally-controlled vents after most of the faulting had ceased. Cut terraces and pediments formed adjacent to the ancestral Rio del Hombre, Subsequent downcutting may have been the result of regional uplift, stream capture along the Rio Choluteca, or both.
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airfall tuffs approximately axiolitic basalt biotite block faulting breccias broken euhedral crystals Caribbean Caribbean plate Carretera del Norte Cenozoic Classification clay Comayagua Comayagua region Comedor Ignimbrite member composition correlated Crystal-vitric ignimbrite Dengo Description devitrified groundmass dike downcutting Everett exposed extruded Fakundiny faulting and erosion fiamme Figure folds formed graben hematite highly welded Honduras ignim indurated interbedded kilometers lacustrine laharic laminated Laramide orogeny Lepaterique Location mafic mafic flows magma main ignimbrite sequence map area Matagalpa Formation McBirney l969 Measured Section meters thick Middle Americas Trench moderately welded nimbrite northwest overlain overlie Padre Miguel Group Paz Quadrangle phenocrysts plagioclase Plate portion probably quartz Quaternary basalt rhyolite rhyolitic domes Rio del Hombre roadcut SAMPLE sanidine shard structure south of Zambrano stream capture Tegucigalpa Tenampua member thin topography trending tuffs unit vitric ignimbrite Vitric-crystal ignimbrite vitrophyre zone volcanic rocks waterlaid Whole and broken Williams and McBirney Younger ignimbrites Zambrano Quadrangle Zambrano region