Stratigraphy of the Chuacús group on the south side of the Sierra de las Minas range, Guatemala

Abstract

The Chuacús Group is a complex of metamorphic rocks in an east-west belt along the Central America Cordillera between the Chixoy-Philochic fault zone to the north and the Motagua fault zone to the south. Newcomb (1975) proposed a stratigraphy for the middle and eastern portions of the Sierra de las Minas range. This investigation attempts to extend that stratigraphy to the western end of the range. To achieve this, some of the formations proposed by Newcomb must be modified, and at least one new formation is introduced. Newcomb's San Augustín Formation is the lowest unit of the Chuacús Group and has not been recognized in the western end of the Sierra de las Minas range. In El Progreso quadrangle several major modifications are needed for the overlying Jones Formation. The mafic composition of this unit may in part be due to metasomatism during Mesozoic to Tertiary serpentinite emplacement. A hornblende gneiss occurs in the lower part of this sequence.