Paleomagnetism of the Acambay graben, central Trans-Mexican Volcanic Belt

摘要: Abstract Paleomagnetic results for Miocene to Quaternary volcanic units of the Acambay graben are used investigate Neogene tectonic activity within central sector Trans-Mexican Volcanic Belt (TMVB). Characteristic magnetization directions were obtained 22 sites, with an overall mean direction (Dec=176.7°, Inc=−34.3°, k =28, α 95 =6°) that is concordant expected calculated from North American reference data. Examination site-mean shows apparent geographic pattern related intersection Queretaro-Taxco fault zone E–W border system graben. This characterized by easterly and westerly declinations arranged into two broad groups. The group A (easterly) ( n =9): Dec=189.9°, Inc=−28.5°, =53 =4.8 . B (westerly) =13): Dec=167.6°, Inc=−36.2°, =38 =4.3°. Group sites cover areas, one inside other immediately south including Pastores fault. distributed over NW SE areas across graben, which include Amealco caldera Epitacio Huerta Acambay–Tixmadeje faults also Venta de Bravo Eighteen show reverse polarities, four normal polarity. Absence polarity suggests a pre-Brunhes age sampled. K–Ar dating in gives range between 5.7 2.2 Ma. comparison 10 Ma pole rotation parameters 9.1±5.3° 9.9±4.6° −12.4±5.4° −12.4±4.3°, respectively. These may be interpreted terms vertical-axis rotations associated regional left-lateral shear normal/strike-slip environment, has during Neogene.