Andrew S. Henry

The MacEachern - Ponsford Memorial Award - 1988

B. Sc. Honours Thesis

The Petrochemistry and Origin of the Bourne Complex, Northwestern Ellesmere Island, Canada

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New petrological and petrochemical analyses provide insight into the origin of the hypabyssal and volcanic rocks of the Bourne Complex, northwestern Ellesmere Island, Canada. Field relationships and petrographic characteristics reveal three groups of igneous rocks within the Complex: 1) Porphyritic Andesite (PA), 2) Plagioclase Porphyry dykes (PD), and 3) North-trending dykes (ND). Immobile trace element, and minor element ratios define the tectonomagmatic character of the Complex. Cluster analysis, using ratios of Y, Nb, Zr, TiO₂, and P₂O₅, confirms the petrographic classification. An Nb/Y - Zr/Ti discrimination diagram indicates that the PA are andesitic, that the PD have subalkaline basalt compositions, and that the ND are alkali basalt transitional to basanite. Ti-Y-Zr and Hf-Ta-Th tectonic discriminator diagrams indicate that the PA belong to a destructive plate margin setting, that the PD indicate a destructive plate margin transitional to backarc basin setting and that the ND show a within plate setting. 40Ar/39Ar isotope dating of primary hornblende from the PA yields an age of 380 +/- 10 mya. The PA may relate to magmatism resulting from the transpressive accretion of the Pearya terrane, ca. 390 mya., whereas the PD likely relate to backarc magmatism resulting from the Ellesmerian Orogeny, ca. 360 mya. Calcalkaline magmatism associated with the docking of Pearya may have been much more widespread than previously suspected.

Keywords: Ellesmere Island, Bourne Complex, Igneous petrology, Calcalkaline magmatism, Trace element geochemistry, Tectonomagmatic discrimination ⁴⁰Ar/³⁹Ar dating
Pages: 128
Supervisor: Gunter Muecke