Cordilleran Section - 108th Annual Meeting (29–31 March 2012)

Paper No. 5
Presentation Time: 10:10


GLADNEY, Evan R., Earth Sciences, Saint Francis Xavier University, Antigonish, NS B2G1K5,

In most cases in continental collision belts plutonic rocks are normally found in the magmatic arc and towards the backarc, however in rare cases the formation and emplacement of syn-collisional plutonic rocks intrude suture zones, and their association with orogenic processes are enigmatic. Southern Iberia records the Late Paleozoic collision of Gondwana (Ossa Morena Zone) with Laurussia (South Portuguese Zone), which resulted in the Variscan orogen, and is an expression of the amalgamation of Pangea in western Europe. This suture zone is stitched by a suite of igneous rocks (Gil Marquez pluton) consisting of coeval mafic and felsic magmas, which display textural evidence of magma mixing and mingling. The generation and emplacement of the Gil Marquez pluton and its relationship to the suture zone are undetermined. Geochemical data combined with structural and petrographic evidence indicate a wide range in composition and indicate two distinct sources for the pluton. A Granodiorite phase prevalent throughout the pluton shows a syn-collisional, east-west foliation similar in orientation to the dominant cleavage in the metasedimentary rocks of the Pulo do Lobo Zone, part of the South Portuguese Zone, and likely represents the regional stress field at the time of emplacement. The gabbro and granite phases are unfoliated and represent the earliest and latest phases of the pluton, respectively. Field evidence shows the emplacement of the Gil Marquez pluton took place in various stages with various sources, as textural relationships between phases within the pluton are well exposed and easily determined. Isotopic and geochronological analyses of critical samples are in progress to determine the isotopic signature of the mantle source of the mafic rocks with the source for late-stage mafic rocks to see if the mantle was emplaced during collision. The goal of this work is to contribute to the understanding of the sources, evolution, and emplacement of magmas in continental collisional zones.
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