Geochemical and geochronological constraints on terrane definition in mexico

Mexico has played host to a variety of igneous events since the Paleozoic, relating to the formation and subsequent breakup of the supercontinent Pangaea, as well as to intermittent subduction along its western coast. Through analysis of the crystalline basement of the Western Gulf of Mexico this project has introduced the first detailed tectonomagmatic model relating to the pre- and post- amalgamation of Pangaea in Mexico. Additionally, post-Pangaea rifting has been investigated in the extensional basin of the northern Cuicateco terrane. This study has identified three igneous events in the crystalline basement of the Western Gulf of Mexico: 1) An Early Permian (294 Ma) continental arc that formed on Gondwana during the final amalgamation of Pangaea. These rocks appear to be related to Late Carboniferous-Early Permian plutons found in the Oaxaca area of Southern Mexico (Ortega-Obregon et al., 2014). 2) Late Permian-Early Triassic (274- 243 Ma) anatectic magmatism that formed in a post-collisional environment after the final amalgamation of Pangaea. These rocks appear to be related to plutons of comparable age found in the Oaxaca area and Chiapas Massif of Southern Mexico (Weber et al., 2005; Ortega-Obregon et al., 2014). 3) Early Jurassic (189-164 Ma) continental arc rocks that likely relate to the Nazas arc system that existed across Mexico at the time (Dickinson & Lawton, 2001). Major element and trace element geochemistry, used in conjunction with Hf and Nd isotopic analysis have revealed that the Early Cretaceous units of the northern Cuicateco terrane formed in a subduction related environment, likely associated with the closure of the Arperos oceanic basin. Extrusive and intrusive arc rocks have been dated between 140-133 Ma (Xonamanca Formation and Teotitlán Migmatitic Complex); with subduction of the Arperos ridge later causing extension (Chivillas Formation). Spreading in the Chivillas Formation stopped in the Earliest Aptian, likely due to the collision of the Guerrero terrane with Mexico.