Thesis advisor: Ethan F. Baxter / The Proterozoic Kipawa Syenite Complex and Red Wine Intrusive Suite have both been explored as potential REE ore bodies and are a heretofore unexploited REE resource. This study improves upon the internal-isochron eudialyte geochronology method developed by Sjöqvist et al. (2020) through the addition of Electron Microprobe mapping prior to precise MicroMill sampling to build Sm/Nd internal mineral isochrons to directly date this potential rare earth element ore mineral. We show that Nb and Ta concentrations correlate well with Sm/Nd ratios in zoned eudialyte crystals, providing a qualitative map to guide microsampling. At the Kipawa Syenite Complex two internal eudialyte isochrons yield ages of 1066±56 Ma (MSWD=1.7) and 1109±53 Ma (MSWD=1.2) while a multi-sample eudialyte bulk isochron produces an age of 1092±53 Ma (MWSD= 1.5). The weighted average of the three isochrons is 1090±31 Ma, and gives the age of eudialyte formation across the Kipawa Syenite Complex. Nd model ages confirm derivation from older continental crust with TDM=2.28. At the Red Wine Intrusive Suite single internal eudialyte isochron yields an age of 765±240 Ma (MSWD=3.7) while the high-Nb sector of this crystal yields an age of 704±120 Ma (MSWD=1.6). A multi-sample eudialyte and mosandrite bulk isochron produces an age of 989± 150 Ma (MSWD=15). The latter age reflects original Grenvillian crystallization of REE ore-minerals, while the age of the high-Nb zone reflects a younger, heretofore unrecognized recrystallization event. Nd model ages suggest derivation from the Proterozoic crust with TDM=1.80. Examination of Nd model ages and geochemical data from five agpaitic deposits (Red Wine, Kipawa, Ilímaussaq, Norra Kärr, Lovozero) reveals three distinct deposit types identified as the Lovozero type, the Grenville type, and the Kipawa type. / Thesis (MS) — Boston College, 2020. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

Understanding crystallisation in magma chambers is a key challenge for igneous petrology. It is particularly important to understand the origins of layering in peralkaline rocks, e.g. the kakortokite (nepheline syenite), Ilímaussaq Complex, S. Greenland, as these are commonly associated with high value multi-element economic deposits. The kakortokite is a spectacular example of macrorhythmic (>5 m) layering. Each unit consists of three layers comprising arfvedsonite-rich (sodic-amphibole) black kakortokite at the base, grading into eudialyte-rich (sodic-zirconosilicate) red kakortokite, then alkali feldspar- and nepheline-rich white kakortokite. Each unit is numbered -19 to +17 relative to a characteristic well-developed horizon (Unit 0), however there is little consensus on their development. This project applies a multidisciplinary approach through field observations combined with petrography, crystal size distributions (CSDs), mineral and whole rock chemistries on Units 0, -8 to -11 and a phonolite/micro-nephelinolite (“hybrid”) sequence that crosscuts the layered kakortokite. Textures and compositions are laterally consistent across outcrop and indicators of current activity are rare. CSDs indicate in situ crystallisation with gravitational settling as a minor process. Chemical discontinuities occur across unit boundaries. The layering developed through large-scale processes under exceptionally quiescent conditions. The discontinuities reflect open-system behaviour; units were formed by an influx of volatile-rich magma that initiated crystallisation in a bottom layer. Nucleation was initially suppressed by high volatile element concentrations, which decreased to allow for crystallisation of arfvedsonite, followed by eudialyte, then alkali feldspar and nepheline to form each tripartite unit. The chemistry of the hybrid indicates mixing between a primitive (sub-alkaline) magma and kakortokite. Thus injections of magmas of varying compositions occurred, indicating a complex plumbing system below current exposure. The lessons learned at Ilímaussaq, which is extremely well exposed and preserved, are relevant to understanding magma chamber dynamics in the more common instances of pervasively altered peralkaline rocks.