Abstract

The Guerrero terrane (western Mexico) is composed of Late Jurassic – Early Cretaceous plutono-volcanic and volcano-sedimentary sequences of the Alisitos–Teloloapan arc that accreted to the North American craton at the end of the Early Cretaceous. The geodynamic evolution of the Guerrero terrane is that of the Alisitos–Teloloapan intraoceanic arc, partly built on continental crust and partly on oceanic crust. The growth of the arc was likely linked to the subduction of the Arperos and Olvidada basins fringing the North American borderland. The subduction was dipping west-south-west.The continent-based segment of the arc, which is presently exposed mainly in northwestern Mexico, is composed of aerial and submarine K-rich calc-alkaline basalts, andesites, and rhyolites and of siliceous pyroclastic rocks interbedded with Aptian–Albian bioclastic carbonates or red beds bearing dinosaurus foot prints. The calc-alkaline basalts and andesites show light rare earth elements enriched patterns and high concentrations in large ion lithophile elements. The siliceous andesites and rhyodacites display low contents in Y and heavy rare earth elements, uncommon for such calc-alkaline SiO2-saturated rocks. This depletion is likely linked to amphibole fractionation and to the presence of sphene and zircon, minerals known to concentrate the heavy rare earth elements.In contrast, the magmatic arc sequences built on oceanic crust, that crops out in central-southern areas of the Guerrero terrane, show an evolution with time. The activity of the arc began with depleted tholeiitic igneous rocks, followed first by mature tholeiitic basalts, then by calc-alkaline olivine basalts interbedded with micritic limestones and radiolarian oozes of Early Cretaceous age (Neocomian). At the end of the arc development, in Late Aptian–Albian, calc-alkaline pillow basalts and andesites erupted at the volcanic front whereas shoshonitic basalts emitted backwards. In the late Early Cretaceous, the arc drifted towards the north and collided with the craton. Arc tholeiites are characterized by flat rare earth element patterns or slightly depleted in light rare earth elements and by high εNd ratios. The calc-alkaline plutonic and volcanic rocks show light rare earth elements enriched patterns and their εNd ratios decrease with time. This decrease of the εNd ratios suggests that either the mantle source of the calc-alkaline rocks was contaminated by subducted terrigenous sediments derived from an old continental crust (North American craton) or that these calc-alkaline rocks derive from the partial melt of an oceanic island basalt source present in the mantle wedge. The shoshonitic features of the basalts are marked by the presence of sanidine in the groundmass and the high levels of K2O, Ba, and Sr of the unaltered rocks.

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