Evaluation of recent tectonomagmatic discrimination diagrams and their application to the origin of basic magmas in southern mexico and central america

摘要

Discrimination diagrams to decipher tectonic settings have been in use for nearly 40 years. Although old diagrams have been extensively used, the recent ones based on discriminant functions of ratio variables, with or without log-transformation, proposed during 2004-2010 for the discrimination of four tectonic settings of island arc, continental rift, ocean-island and mid-ocean ridge, were newly evaluated to show their high success rates of 57.3-100% and 58.5-100% for major-element and immobile-element based diagrams, respectively. For the continental arc of the Andes evaluated for its similarity to island arc, these four sets of diagrams showed success rates of 62.1-83.8%. These four sets of five diagrams per set were therefore used to infer tectonic setting of the Mexican Volcanic Belt (MVB), Los Tuxtlas volcanic field (LTVF), and Central American Volcanic Arc (CAVA). Using this approach, the MVB, especially its western, central and eastern parts, and the LTVF of Southern Mexico show a dominantly continental rift setting and the CAVA shows an arc setting. The west-central part of the MVB is consistent with dual tectonics of arc and rift. These results confirm the application of an unusual mantle upwelling rift-model for the Mexican on-land volcanism, whereas the conventional plate tectonic subduction model seems to be applicable for the CAVA from Guatemala to north-western Costa Rica.