Southward migration of volcanic activity in the Sierra de Las Cruces, basin of Mexico? - A preliminary K -Ar dating and palaeomagnetic study

Abstract

K-Ar dates and palaeomagnetic data are reported for a suite of volcanic rocks from Sierra de Las Cruces, Basin of Mexico. The NNW -SSE volcanic range is predominantly built of dacitic lavas, pyroclastic units and lahars and constitutes the western limit of the basin. This preliminary study was designed to investigate the volcanic stratigraphy of the Sierra and to document an apparent spatial migration of volcanic activity along the range. The sampling profile followed the trend of the Sierra. The five units selected for the study comprised four andesitic flows and a basaltic flow. Results are summarized below in terms of K-Ar dates and magnetic polarity chrons: Unit, Date (Ma), Polarity, Polarity Chron: Ajusco, O.39±O.l6, Normal, Brunhes; Ajusco, Intermediate (R), Brunhes; M. Contreras, l.92±O.13, Reverse, Matuyama; D. Leones, l.79±O.1O, Intermediate (N), Matuyama; Huixquilucan, 2.76±O.l9, Normal, Gauss; Peñas Cuatas, 2.87±O.15. Results document an apparent southward migration of volcanic activity and suggest an age range of Pliocene to Plcistocene for the formation of the Sierra de las Cruces. This spatial-temporal migration correlates with apparently similar trends of volcanic activity in the Trans-Mexican volcanic belt. Further studies are required to establish any regional characteristics and implications.