Geochemical constraints on the origin of mafic and ultrapotassic dykes from the southern Manicouagan area, Grenville province

• Main Author: Valverde Cardenas, Carolina
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 2009
• Subjects: Makkovik
• Online Access: https://research.library.mun.ca/9152/; https://research.library.mun.ca/9152/1/Cardenas_CarolinaValverde.pdf

The Grenville Province has a long record of magmatic activity, including arc magmatism related to the pre-Grenvillian evolution of eastern Laurentia and magmatism during the final collision that shaped the orogen. This study focuses on recently identified mafic dykes exposed in the Gagnon Terrane and the Canyon Domain as well as late tectonic, ultrapotassic dykes exposed in the Canyon Domain, in the central part of the Province. -- In the Gagnon Terrane, mafic dykes inferred to be ~1.74 Ga old, intrude Archean orthogneisses east of a major shear zone. These dykes are foliated and recrystallized under upper amphibolite to granulite facies conditions. These rocks have a geochemical signature of subalkaline tholeiitic basalts to andesites and, some, show primitive Mg#, Cr and Ni contents. Epsilon Nd values (at 1.75 Ga) range from +1.1 to +2.1, to highly negative (-17.9). The geochemical data and presumed age suggest that the dykes represent mantle-derived melts variably contaminated by crust. The ~1.74 Ga magmatic event in Gagnon Terrane is coeval with late orogenic magmatism in the Makkovik Province and provides a hint for potentially widespread 1.7 Ga magmatism into the Laurentian margin. -- In the Canyon Domain, mafic dykes intrude a ~1.4 Ga volcanoclastic sequence, inferred to represent remnants of an island arc, in the vicinity of a ~1.2 Ga bimodal sequence inferred to have formed in a back arc setting. These dykes are variably deformed and recrystallized under medium-P granulite facies conditions. These dykes have a geochemical signature of subalkaline tholeiitic basalts to andesites, similar REE patterns and εNd¹³⁰⁰ values from +4.6 to +6.2. However, two groups have been recognized based on the presence (Group 2) or absence (Group 1) of pronounced negative Nb anomalies. The dykes of Group 2 have an arc geochemical signature and may have been emplaced during late stages of the development of the ~1.4 Ga arc. In contrast, the dykes of Group 1 have a within-plate geochemical signature and may be correlative ...