Sydney Stashin

B.Sc. (Honours) Thesis

Investigating possible hybridization of the Peggys Cove granite section of the Halifax Pluton, South Mountain Batholith, Nova Scotia

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This study performed an investigation of magmatic growth history of the K-feldspar megacrysts and plagioclase crystals in the Halifax Pluton, a Late Devonian age granite that intruded into the Meguma strata bedrock. We used the growth histories of these crystals to examine the extent of hybridization in three sections of the Halifax Pluton: Peggy’s Cove, Prospect, and Sambro Head. Several outcrops in the Peggys Cove and Prospect section of the pluton contain clusters of large mafic enclaves, which differ texturally from country-rock, metasedimentary xenoliths, and appear to be of a magmatic origin. Of note are enclaves that show megacrysts crosscutting their margins, suggesting that both the host granite and enclave were at least partially liquid during megacryst growth and magma mixing could have occurred. A mafic dyke has been documented at Sambro Head, with several zones of magma mingling suggesting it was injected as a partial liquid into the granitic ground mass. This study used field observations, petrography, and detailed electron microprobe analysis to study the large K-feldspar megacrysts and smaller plagioclase crystals from the granite sections at Prospect, Peggys Cove, and Sambro Head. Samples from within the mafic dyke at Sambro Head were also analyzed. Evidence suggests that a variable extent of magma mixing/mingling and hybridization occurred and this is reflected in the different textures recorded by these megacrysts from each phase of the pluton. Evidence of chemical zoning preserved in the K-feldspar megacrysts and plagioclase crystals, especially where no obvious mafic enclaves or dykes are present, suggests that hybridization of this granitic pluton may have been more widespread than previously documented. The presence of mafic dykes does not necessarily provide evidence of mixing; on the contrary it is the absence of mafic dykes at these sites that indicate extensive hybridization may have occurred.

Keywords: megacryst, resorption, dyke, zoning, hybridization
Pages: 80
Supervisor: Richard Cox