Preliminary palaeomagnetic study of lower tertiary volcanic rocks from Morelos and Guerrero states

Abstract

Mean palaeomagnetic directions and pole positions deriven from seven lower Tertiary volcanic units exposed in central-southern Mexico after alternating field and thermal demagnetization diverge from corresponding data of northern Mexico. The studied unists are two lavas of the Palaeocene-Eocene Balsas Formation, two tuffs of the Riolita Tilzapotla (K-Ar date of 49 ± 3 m.y.) And two tuffs and an andesitic lava of Miocene (?) Volcanics. The results could be explained in terms of relative counterclockwise tectonic rotations of the sampling areas, possibly associated with regional compression and shear acting on blocks cut by large lateral strike-dip faults. However, we feel that more data are required to support this interpretation before a tectonic model can be put forth.