Geological and geochemical investigations on the eastern trans mexican volcanic belt.

This paper reports upon geological and geochemical investigations of the easternmost extension of the Trans Mexican Volcanic Belt (TMVB). As a result of our work we prefer to consider that the TMVB terminates at the Gulf coast and not in the Altiplano area (e.g. Robin, 1981), with respect to a Pliocene-Quaternary volcanic activity. During that time the volcanism is of calcalkaline and alkaline character. The older volcanic activity, e.g. of Miocene times, produced alkaline-calcalkaline igneous rocks in the Massif de Palma Sola and calcalkaline igneous rocks in the western part of Mexico due to the eastwest migration of the subduction of the Palaeopacific plate (Robin, 1976). Our geochemical results neither deny nor favour one single geological model and do not even exclude the microplate version of Shurbet and Cebull (1984). However, the geochemical data cannot be explained by direct derivation of the volcanics from the oceanic lithosphere (e.g. Robin, 1981, 1982). Irrespective of this fact, the volcanism of the TMVB suggests to be caused or induced by the subduction of the Rivera and Cocos plate association.